[LogFS] add new flash file system

This is a new flash file system. See
Documentation/filesystems/logfs.txt

Signed-off-by: Joern Engel <[e-mail]>

Documentation/filesystems/00-INDEX

···
 	- info and mount options for the JFS filesystem.
 locks.txt
 	- info on file locking implementations, flock() vs. fcntl(), etc.
+logfs.txt
+	- info on the LogFS flash filesystem.
 mandatory-locking.txt
 	- info on the Linux implementation of Sys V mandatory file locking.
 ncpfs.txt

Documentation/filesystems/logfs.txt

···
+
+The LogFS Flash Filesystem
+==========================
+
+Specification
+=============
+
+Superblocks
+-----------
+
+Two superblocks exist at the beginning and end of the filesystem.
+Each superblock is 256 Bytes large, with another 3840 Bytes reserved
+for future purposes, making a total of 4096 Bytes.
+
+Superblock locations may differ for MTD and block devices.  On MTD the
+first non-bad block contains a superblock in the first 4096 Bytes and
+the last non-bad block contains a superblock in the last 4096 Bytes.
+On block devices, the first 4096 Bytes of the device contain the first
+superblock and the last aligned 4096 Byte-block contains the second
+superblock.
+
+For the most part, the superblocks can be considered read-only.  They
+are written only to correct errors detected within the superblocks,
+move the journal and change the filesystem parameters through tunefs.
+As a result, the superblock does not contain any fields that require
+constant updates, like the amount of free space, etc.
+
+Segments
+--------
+
+The space in the device is split up into equal-sized segments.
+Segments are the primary write unit of LogFS.  Within each segments,
+writes happen from front (low addresses) to back (high addresses.  If
+only a partial segment has been written, the segment number, the
+current position within and optionally a write buffer are stored in
+the journal.
+
+Segments are erased as a whole.  Therefore Garbage Collection may be
+required to completely free a segment before doing so.
+
+Journal
+--------
+
+The journal contains all global information about the filesystem that
+is subject to frequent change.  At mount time, it has to be scanned
+for the most recent commit entry, which contains a list of pointers to
+all currently valid entries.
+
+Object Store
+------------
+
+All space except for the superblocks and journal is part of the object
+store.  Each segment contains a segment header and a number of
+objects, each consisting of the object header and the payload.
+Objects are either inodes, directory entries (dentries), file data
+blocks or indirect blocks.
+
+Levels
+------
+
+Garbage collection (GC) may fail if all data is written
+indiscriminately.  One requirement of GC is that data is seperated
+roughly according to the distance between the tree root and the data.
+Effectively that means all file data is on level 0, indirect blocks
+are on levels 1, 2, 3 4 or 5 for 1x, 2x, 3x, 4x or 5x indirect blocks,
+respectively.  Inode file data is on level 6 for the inodes and 7-11
+for indirect blocks.
+
+Each segment contains objects of a single level only.  As a result,
+each level requires its own seperate segment to be open for writing.
+
+Inode File
+----------
+
+All inodes are stored in a special file, the inode file.  Single
+exception is the inode file's inode (master inode) which for obvious
+reasons is stored in the journal instead.  Instead of data blocks, the
+leaf nodes of the inode files are inodes.
+
+Aliases
+-------
+
+Writes in LogFS are done by means of a wandering tree.  A naïve
+implementation would require that for each write or a block, all
+parent blocks are written as well, since the block pointers have
+changed.  Such an implementation would not be very efficient.
+
+In LogFS, the block pointer changes are cached in the journal by means
+of alias entries.  Each alias consists of its logical address - inode
+number, block index, level and child number (index into block) - and
+the changed data.  Any 8-byte word can be changes in this manner.
+
+Currently aliases are used for block pointers, file size, file used
+bytes and the height of an inodes indirect tree.
+
+Segment Aliases
+---------------
+
+Related to regular aliases, these are used to handle bad blocks.
+Initially, bad blocks are handled by moving the affected segment
+content to a spare segment and noting this move in the journal with a
+segment alias, a simple (to, from) tupel.  GC will later empty this
+segment and the alias can be removed again.  This is used on MTD only.
+
+Vim
+---
+
+By cleverly predicting the life time of data, it is possible to
+seperate long-living data from short-living data and thereby reduce
+the GC overhead later.  Each type of distinc life expectency (vim) can
+have a seperate segment open for writing.  Each (level, vim) tupel can
+be open just once.  If an open segment with unknown vim is encountered
+at mount time, it is closed and ignored henceforth.
+
+Indirect Tree
+-------------
+
+Inodes in LogFS are similar to FFS-style filesystems with direct and
+indirect block pointers.  One difference is that LogFS uses a single
+indirect pointer that can be either a 1x, 2x, etc. indirect pointer.
+A height field in the inode defines the height of the indirect tree
+and thereby the indirection of the pointer.
+
+Another difference is the addressing of indirect blocks.  In LogFS,
+the first 16 pointers in the first indirect block are left empty,
+corresponding to the 16 direct pointers in the inode.  In ext2 (maybe
+others as well) the first pointer in the first indirect block
+corresponds to logical block 12, skipping the 12 direct pointers.
+So where ext2 is using arithmetic to better utilize space, LogFS keeps
+arithmetic simple and uses compression to save space.
+
+Compression
+-----------
+
+Both file data and metadata can be compressed.  Compression for file
+data can be enabled with chattr +c and disabled with chattr -c.  Doing
+so has no effect on existing data, but new data will be stored
+accordingly.  New inodes will inherit the compression flag of the
+parent directory.
+
+Metadata is always compressed.  However, the space accounting ignores
+this and charges for the uncompressed size.  Failing to do so could
+result in GC failures when, after moving some data, indirect blocks
+compress worse than previously.  Even on a 100% full medium, GC may
+not consume any extra space, so the compression gains are lost space
+to the user.
+
+However, they are not lost space to the filesystem internals.  By
+cheating the user for those bytes, the filesystem gained some slack
+space and GC will run less often and faster.
+
+Garbage Collection and Wear Leveling
+------------------------------------
+
+Garbage collection is invoked whenever the number of free segments
+falls below a threshold.  The best (known) candidate is picked based
+on the least amount of valid data contained in the segment.  All
+remaining valid data is copied elsewhere, thereby invalidating it.
+
+The GC code also checks for aliases and writes then back if their
+number gets too large.
+
+Wear leveling is done by occasionally picking a suboptimal segment for
+garbage collection.  If a stale segments erase count is significantly
+lower than the active segments' erase counts, it will be picked.  Wear
+leveling is rate limited, so it will never monopolize the device for
+more than one segment worth at a time.
+
+Values for "occasionally", "significantly lower" are compile time
+constants.
+
+Hashed directories
+------------------
+
+To satisfy efficient lookup(), directory entries are hashed and
+located based on the hash.  In order to both support large directories
+and not be overly inefficient for small directories, several hash
+tables of increasing size are used.  For each table, the hash value
+modulo the table size gives the table index.
+
+Tables sizes are chosen to limit the number of indirect blocks with a
+fully populated table to 0, 1, 2 or 3 respectively.  So the first
+table contains 16 entries, the second 512-16, etc.
+
+The last table is special in several ways.  First its size depends on
+the effective 32bit limit on telldir/seekdir cookies.  Since logfs
+uses the upper half of the address space for indirect blocks, the size
+is limited to 2^31.  Secondly the table contains hash buckets with 16
+entries each.
+
+Using single-entry buckets would result in birthday "attacks".  At
+just 2^16 used entries, hash collisions would be likely (P >= 0.5).
+My math skills are insufficient to do the combinatorics for the 17x
+collisions necessary to overflow a bucket, but testing showed that in
+10,000 runs the lowest directory fill before a bucket overflow was
+188,057,130 entries with an average of 315,149,915 entries.  So for
+directory sizes of up to a million, bucket overflows should be
+virtually impossible under normal circumstances.
+
+With carefully chosen filenames, it is obviously possible to cause an
+overflow with just 21 entries (4 higher tables + 16 entries + 1).  So
+there may be a security concern if a malicious user has write access
+to a directory.
+
+Open For Discussion
+===================
+
+Device Address Space
+--------------------
+
+A device address space is used for caching.  Both block devices and
+MTD provide functions to either read a single page or write a segment.
+Partial segments may be written for data integrity, but where possible
+complete segments are written for performance on simple block device
+flash media.
+
+Meta Inodes
+-----------
+
+Inodes are stored in the inode file, which is just a regular file for
+most purposes.  At umount time, however, the inode file needs to
+remain open until all dirty inodes are written.  So
+generic_shutdown_super() may not close this inode, but shouldn't
+complain about remaining inodes due to the inode file either.  Same
+goes for mapping inode of the device address space.
+
+Currently logfs uses a hack that essentially copies part of fs/inode.c
+code over.  A general solution would be preferred.
+
+Indirect block mapping
+----------------------
+
+With compression, the block device (or mapping inode) cannot be used
+to cache indirect blocks.  Some other place is required.  Currently
+logfs uses the top half of each inode's address space.  The low 8TB
+(on 32bit) are filled with file data, the high 8TB are used for
+indirect blocks.
+
+One problem is that 16TB files created on 64bit systems actually have
+data in the top 8TB.  But files >16TB would cause problems anyway, so
+only the limit has changed.

fs/Kconfig

···
 source "fs/jffs2/Kconfig"
 # UBIFS File system configuration
 source "fs/ubifs/Kconfig"
+source "fs/logfs/Kconfig"
 source "fs/cramfs/Kconfig"
 source "fs/squashfs/Kconfig"
 source "fs/freevxfs/Kconfig"

fs/Makefile

···
 obj-$(CONFIG_UFS_FS)		+= ufs/
 obj-$(CONFIG_EFS_FS)		+= efs/
 obj-$(CONFIG_JFFS2_FS)		+= jffs2/
+obj-$(CONFIG_LOGFS)		+= logfs/
 obj-$(CONFIG_UBIFS_FS)		+= ubifs/
 obj-$(CONFIG_AFFS_FS)		+= affs/
 obj-$(CONFIG_ROMFS_FS)		+= romfs/

fs/logfs/Kconfig

···
+config LOGFS
+	tristate "LogFS file system (EXPERIMENTAL)"
+	depends on (MTD || BLOCK) && EXPERIMENTAL
+	select ZLIB_INFLATE
+	select ZLIB_DEFLATE
+	select CRC32
+	select BTREE
+	help
+	  Flash filesystem aimed to scale efficiently to large devices.
+	  In comparison to JFFS2 it offers significantly faster mount
+	  times and potentially less RAM usage, although the latter has
+	  not been measured yet.
+
+	  In its current state it is still very experimental and should
+	  not be used for other than testing purposes.
+
+	  If unsure, say N.

fs/logfs/Makefile

···
+obj-$(CONFIG_LOGFS)	+= logfs.o
+
+logfs-y	+= compr.o
+logfs-y	+= dir.o
+logfs-y	+= file.o
+logfs-y	+= gc.o
+logfs-y	+= inode.o
+logfs-y	+= journal.o
+logfs-y	+= readwrite.o
+logfs-y	+= segment.o
+logfs-y	+= super.o
+logfs-$(CONFIG_BLOCK)	+= dev_bdev.o
+logfs-$(CONFIG_MTD)	+= dev_mtd.o

fs/logfs/compr.c

···
+/*
+ * fs/logfs/compr.c	- compression routines
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+
+#define COMPR_LEVEL 3
+
+static DEFINE_MUTEX(compr_mutex);
+static struct z_stream_s stream;
+
+int logfs_compress(void *in, void *out, size_t inlen, size_t outlen)
+{
+	int err, ret;
+
+	ret = -EIO;
+	mutex_lock(&compr_mutex);
+	err = zlib_deflateInit(&stream, COMPR_LEVEL);
+	if (err != Z_OK)
+		goto error;
+
+	stream.next_in = in;
+	stream.avail_in = inlen;
+	stream.total_in = 0;
+	stream.next_out = out;
+	stream.avail_out = outlen;
+	stream.total_out = 0;
+
+	err = zlib_deflate(&stream, Z_FINISH);
+	if (err != Z_STREAM_END)
+		goto error;
+
+	err = zlib_deflateEnd(&stream);
+	if (err != Z_OK)
+		goto error;
+
+	if (stream.total_out >= stream.total_in)
+		goto error;
+
+	ret = stream.total_out;
+error:
+	mutex_unlock(&compr_mutex);
+	return ret;
+}
+
+int logfs_uncompress(void *in, void *out, size_t inlen, size_t outlen)
+{
+	int err, ret;
+
+	ret = -EIO;
+	mutex_lock(&compr_mutex);
+	err = zlib_inflateInit(&stream);
+	if (err != Z_OK)
+		goto error;
+
+	stream.next_in = in;
+	stream.avail_in = inlen;
+	stream.total_in = 0;
+	stream.next_out = out;
+	stream.avail_out = outlen;
+	stream.total_out = 0;
+
+	err = zlib_inflate(&stream, Z_FINISH);
+	if (err != Z_STREAM_END)
+		goto error;
+
+	err = zlib_inflateEnd(&stream);
+	if (err != Z_OK)
+		goto error;
+
+	ret = 0;
+error:
+	mutex_unlock(&compr_mutex);
+	return ret;
+}
+
+int __init logfs_compr_init(void)
+{
+	size_t size = max(zlib_deflate_workspacesize(),
+			zlib_inflate_workspacesize());
+	stream.workspace = vmalloc(size);
+	if (!stream.workspace)
+		return -ENOMEM;
+	return 0;
+}
+
+void logfs_compr_exit(void)
+{
+	vfree(stream.workspace);
+}

fs/logfs/dev_bdev.c

···
+/*
+ * fs/logfs/dev_bdev.c	- Device access methods for block devices
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>
+
+#define PAGE_OFS(ofs) ((ofs) & (PAGE_SIZE-1))
+
+static void request_complete(struct bio *bio, int err)
+{
+	complete((struct completion *)bio->bi_private);
+}
+
+static int sync_request(struct page *page, struct block_device *bdev, int rw)
+{
+	struct bio bio;
+	struct bio_vec bio_vec;
+	struct completion complete;
+
+	bio_init(&bio);
+	bio.bi_io_vec = &bio_vec;
+	bio_vec.bv_page = page;
+	bio_vec.bv_len = PAGE_SIZE;
+	bio_vec.bv_offset = 0;
+	bio.bi_vcnt = 1;
+	bio.bi_idx = 0;
+	bio.bi_size = PAGE_SIZE;
+	bio.bi_bdev = bdev;
+	bio.bi_sector = page->index * (PAGE_SIZE >> 9);
+	init_completion(&complete);
+	bio.bi_private = &complete;
+	bio.bi_end_io = request_complete;
+
+	submit_bio(rw, &bio);
+	generic_unplug_device(bdev_get_queue(bdev));
+	wait_for_completion(&complete);
+	return test_bit(BIO_UPTODATE, &bio.bi_flags) ? 0 : -EIO;
+}
+
+static int bdev_readpage(void *_sb, struct page *page)
+{
+	struct super_block *sb = _sb;
+	struct block_device *bdev = logfs_super(sb)->s_bdev;
+	int err;
+
+	err = sync_request(page, bdev, READ);
+	if (err) {
+		ClearPageUptodate(page);
+		SetPageError(page);
+	} else {
+		SetPageUptodate(page);
+		ClearPageError(page);
+	}
+	unlock_page(page);
+	return err;
+}
+
+static DECLARE_WAIT_QUEUE_HEAD(wq);
+
+static void writeseg_end_io(struct bio *bio, int err)
+{
+	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
+	struct bio_vec *bvec = bio->bi_io_vec + bio->bi_vcnt - 1;
+	struct super_block *sb = bio->bi_private;
+	struct logfs_super *super = logfs_super(sb);
+	struct page *page;
+
+	BUG_ON(!uptodate); /* FIXME: Retry io or write elsewhere */
+	BUG_ON(err);
+	BUG_ON(bio->bi_vcnt == 0);
+	do {
+		page = bvec->bv_page;
+		if (--bvec >= bio->bi_io_vec)
+			prefetchw(&bvec->bv_page->flags);
+
+		end_page_writeback(page);
+	} while (bvec >= bio->bi_io_vec);
+	bio_put(bio);
+	if (atomic_dec_and_test(&super->s_pending_writes))
+		wake_up(&wq);
+}
+
+static int __bdev_writeseg(struct super_block *sb, u64 ofs, pgoff_t index,
+		size_t nr_pages)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	struct bio *bio;
+	struct page *page;
+	struct request_queue *q = bdev_get_queue(sb->s_bdev);
+	unsigned int max_pages = queue_max_hw_sectors(q) >> (PAGE_SHIFT - 9);
+	int i;
+
+	bio = bio_alloc(GFP_NOFS, max_pages);
+	BUG_ON(!bio); /* FIXME: handle this */
+
+	for (i = 0; i < nr_pages; i++) {
+		if (i >= max_pages) {
+			/* Block layer cannot split bios :( */
+			bio->bi_vcnt = i;
+			bio->bi_idx = 0;
+			bio->bi_size = i * PAGE_SIZE;
+			bio->bi_bdev = super->s_bdev;
+			bio->bi_sector = ofs >> 9;
+			bio->bi_private = sb;
+			bio->bi_end_io = writeseg_end_io;
+			atomic_inc(&super->s_pending_writes);
+			submit_bio(WRITE, bio);
+
+			ofs += i * PAGE_SIZE;
+			index += i;
+			nr_pages -= i;
+			i = 0;
+
+			bio = bio_alloc(GFP_NOFS, max_pages);
+			BUG_ON(!bio);
+		}
+		page = find_lock_page(mapping, index + i);
+		BUG_ON(!page);
+		bio->bi_io_vec[i].bv_page = page;
+		bio->bi_io_vec[i].bv_len = PAGE_SIZE;
+		bio->bi_io_vec[i].bv_offset = 0;
+
+		BUG_ON(PageWriteback(page));
+		set_page_writeback(page);
+		unlock_page(page);
+	}
+	bio->bi_vcnt = nr_pages;
+	bio->bi_idx = 0;
+	bio->bi_size = nr_pages * PAGE_SIZE;
+	bio->bi_bdev = super->s_bdev;
+	bio->bi_sector = ofs >> 9;
+	bio->bi_private = sb;
+	bio->bi_end_io = writeseg_end_io;
+	atomic_inc(&super->s_pending_writes);
+	submit_bio(WRITE, bio);
+	return 0;
+}
+
+static void bdev_writeseg(struct super_block *sb, u64 ofs, size_t len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int head;
+
+	BUG_ON(super->s_flags & LOGFS_SB_FLAG_RO);
+
+	if (len == 0) {
+		/* This can happen when the object fit perfectly into a
+		 * segment, the segment gets written per sync and subsequently
+		 * closed.
+		 */
+		return;
+	}
+	head = ofs & (PAGE_SIZE - 1);
+	if (head) {
+		ofs -= head;
+		len += head;
+	}
+	len = PAGE_ALIGN(len);
+	__bdev_writeseg(sb, ofs, ofs >> PAGE_SHIFT, len >> PAGE_SHIFT);
+	generic_unplug_device(bdev_get_queue(logfs_super(sb)->s_bdev));
+}
+
+static int bdev_erase(struct super_block *sb, loff_t to, size_t len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	struct page *page;
+	pgoff_t index = to >> PAGE_SHIFT;
+	int i, nr_pages = len >> PAGE_SHIFT;
+
+	BUG_ON(to & (PAGE_SIZE - 1));
+	BUG_ON(len & (PAGE_SIZE - 1));
+
+	if (logfs_super(sb)->s_flags & LOGFS_SB_FLAG_RO)
+		return -EROFS;
+
+	for (i = 0; i < nr_pages; i++) {
+		page = find_get_page(mapping, index + i);
+		if (page) {
+			memset(page_address(page), 0xFF, PAGE_SIZE);
+			page_cache_release(page);
+		}
+	}
+	return 0;
+}
+
+static void bdev_sync(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	wait_event(wq, atomic_read(&super->s_pending_writes) == 0);
+}
+
+static struct page *bdev_find_first_sb(struct super_block *sb, u64 *ofs)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	filler_t *filler = bdev_readpage;
+
+	*ofs = 0;
+	return read_cache_page(mapping, 0, filler, sb);
+}
+
+static struct page *bdev_find_last_sb(struct super_block *sb, u64 *ofs)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	filler_t *filler = bdev_readpage;
+	u64 pos = (super->s_bdev->bd_inode->i_size & ~0xfffULL) - 0x1000;
+	pgoff_t index = pos >> PAGE_SHIFT;
+
+	*ofs = pos;
+	return read_cache_page(mapping, index, filler, sb);
+}
+
+static int bdev_write_sb(struct super_block *sb, struct page *page)
+{
+	struct block_device *bdev = logfs_super(sb)->s_bdev;
+
+	/* Nothing special to do for block devices. */
+	return sync_request(page, bdev, WRITE);
+}
+
+static void bdev_put_device(struct super_block *sb)
+{
+	close_bdev_exclusive(logfs_super(sb)->s_bdev, FMODE_READ|FMODE_WRITE);
+}
+
+static const struct logfs_device_ops bd_devops = {
+	.find_first_sb	= bdev_find_first_sb,
+	.find_last_sb	= bdev_find_last_sb,
+	.write_sb	= bdev_write_sb,
+	.readpage	= bdev_readpage,
+	.writeseg	= bdev_writeseg,
+	.erase		= bdev_erase,
+	.sync		= bdev_sync,
+	.put_device	= bdev_put_device,
+};
+
+int logfs_get_sb_bdev(struct file_system_type *type, int flags,
+		const char *devname, struct vfsmount *mnt)
+{
+	struct block_device *bdev;
+
+	bdev = open_bdev_exclusive(devname, FMODE_READ|FMODE_WRITE, type);
+	if (IS_ERR(bdev))
+		return PTR_ERR(bdev);
+
+	if (MAJOR(bdev->bd_dev) == MTD_BLOCK_MAJOR) {
+		int mtdnr = MINOR(bdev->bd_dev);
+		close_bdev_exclusive(bdev, FMODE_READ|FMODE_WRITE);
+		return logfs_get_sb_mtd(type, flags, mtdnr, mnt);
+	}
+
+	return logfs_get_sb_device(type, flags, NULL, bdev, &bd_devops, mnt);
+}

fs/logfs/dev_mtd.c

···
+/*
+ * fs/logfs/dev_mtd.c	- Device access methods for MTD
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/completion.h>
+#include <linux/mount.h>
+#include <linux/sched.h>
+
+#define PAGE_OFS(ofs) ((ofs) & (PAGE_SIZE-1))
+
+static int mtd_read(struct super_block *sb, loff_t ofs, size_t len, void *buf)
+{
+	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
+	size_t retlen;
+	int ret;
+
+	ret = mtd->read(mtd, ofs, len, &retlen, buf);
+	BUG_ON(ret == -EINVAL);
+	if (ret)
+		return ret;
+
+	/* Not sure if we should loop instead. */
+	if (retlen != len)
+		return -EIO;
+
+	return 0;
+}
+
+static int mtd_write(struct super_block *sb, loff_t ofs, size_t len, void *buf)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct mtd_info *mtd = super->s_mtd;
+	size_t retlen;
+	loff_t page_start, page_end;
+	int ret;
+
+	if (super->s_flags & LOGFS_SB_FLAG_RO)
+		return -EROFS;
+
+	BUG_ON((ofs >= mtd->size) || (len > mtd->size - ofs));
+	BUG_ON(ofs != (ofs >> super->s_writeshift) << super->s_writeshift);
+	BUG_ON(len > PAGE_CACHE_SIZE);
+	page_start = ofs & PAGE_CACHE_MASK;
+	page_end = PAGE_CACHE_ALIGN(ofs + len) - 1;
+	ret = mtd->write(mtd, ofs, len, &retlen, buf);
+	if (ret || (retlen != len))
+		return -EIO;
+
+	return 0;
+}
+
+/*
+ * For as long as I can remember (since about 2001) mtd->erase has been an
+ * asynchronous interface lacking the first driver to actually use the
+ * asynchronous properties.  So just to prevent the first implementor of such
+ * a thing from breaking logfs in 2350, we do the usual pointless dance to
+ * declare a completion variable and wait for completion before returning
+ * from mtd_erase().  What an excercise in futility!
+ */
+static void logfs_erase_callback(struct erase_info *ei)
+{
+	complete((struct completion *)ei->priv);
+}
+
+static int mtd_erase_mapping(struct super_block *sb, loff_t ofs, size_t len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	struct page *page;
+	pgoff_t index = ofs >> PAGE_SHIFT;
+
+	for (index = ofs >> PAGE_SHIFT; index < (ofs + len) >> PAGE_SHIFT; index++) {
+		page = find_get_page(mapping, index);
+		if (!page)
+			continue;
+		memset(page_address(page), 0xFF, PAGE_SIZE);
+		page_cache_release(page);
+	}
+	return 0;
+}
+
+static int mtd_erase(struct super_block *sb, loff_t ofs, size_t len)
+{
+	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
+	struct erase_info ei;
+	DECLARE_COMPLETION_ONSTACK(complete);
+	int ret;
+
+	BUG_ON(len % mtd->erasesize);
+	if (logfs_super(sb)->s_flags & LOGFS_SB_FLAG_RO)
+		return -EROFS;
+
+	memset(&ei, 0, sizeof(ei));
+	ei.mtd = mtd;
+	ei.addr = ofs;
+	ei.len = len;
+	ei.callback = logfs_erase_callback;
+	ei.priv = (long)&complete;
+	ret = mtd->erase(mtd, &ei);
+	if (ret)
+		return -EIO;
+
+	wait_for_completion(&complete);
+	if (ei.state != MTD_ERASE_DONE)
+		return -EIO;
+	return mtd_erase_mapping(sb, ofs, len);
+}
+
+static void mtd_sync(struct super_block *sb)
+{
+	struct mtd_info *mtd = logfs_super(sb)->s_mtd;
+
+	if (mtd->sync)
+		mtd->sync(mtd);
+}
+
+static int mtd_readpage(void *_sb, struct page *page)
+{
+	struct super_block *sb = _sb;
+	int err;
+
+	err = mtd_read(sb, page->index << PAGE_SHIFT, PAGE_SIZE,
+			page_address(page));
+	if (err == -EUCLEAN) {
+		err = 0;
+		/* FIXME: force GC this segment */
+	}
+	if (err) {
+		ClearPageUptodate(page);
+		SetPageError(page);
+	} else {
+		SetPageUptodate(page);
+		ClearPageError(page);
+	}
+	unlock_page(page);
+	return err;
+}
+
+static struct page *mtd_find_first_sb(struct super_block *sb, u64 *ofs)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	filler_t *filler = mtd_readpage;
+	struct mtd_info *mtd = super->s_mtd;
+
+	if (!mtd->block_isbad)
+		return NULL;
+
+	*ofs = 0;
+	while (mtd->block_isbad(mtd, *ofs)) {
+		*ofs += mtd->erasesize;
+		if (*ofs >= mtd->size)
+			return NULL;
+	}
+	BUG_ON(*ofs & ~PAGE_MASK);
+	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
+}
+
+static struct page *mtd_find_last_sb(struct super_block *sb, u64 *ofs)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	filler_t *filler = mtd_readpage;
+	struct mtd_info *mtd = super->s_mtd;
+
+	if (!mtd->block_isbad)
+		return NULL;
+
+	*ofs = mtd->size - mtd->erasesize;
+	while (mtd->block_isbad(mtd, *ofs)) {
+		*ofs -= mtd->erasesize;
+		if (*ofs <= 0)
+			return NULL;
+	}
+	*ofs = *ofs + mtd->erasesize - 0x1000;
+	BUG_ON(*ofs & ~PAGE_MASK);
+	return read_cache_page(mapping, *ofs >> PAGE_SHIFT, filler, sb);
+}
+
+static int __mtd_writeseg(struct super_block *sb, u64 ofs, pgoff_t index,
+		size_t nr_pages)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	struct page *page;
+	int i, err;
+
+	for (i = 0; i < nr_pages; i++) {
+		page = find_lock_page(mapping, index + i);
+		BUG_ON(!page);
+
+		err = mtd_write(sb, page->index << PAGE_SHIFT, PAGE_SIZE,
+				page_address(page));
+		unlock_page(page);
+		page_cache_release(page);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+static void mtd_writeseg(struct super_block *sb, u64 ofs, size_t len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int head;
+
+	if (super->s_flags & LOGFS_SB_FLAG_RO)
+		return;
+
+	if (len == 0) {
+		/* This can happen when the object fit perfectly into a
+		 * segment, the segment gets written per sync and subsequently
+		 * closed.
+		 */
+		return;
+	}
+	head = ofs & (PAGE_SIZE - 1);
+	if (head) {
+		ofs -= head;
+		len += head;
+	}
+	len = PAGE_ALIGN(len);
+	__mtd_writeseg(sb, ofs, ofs >> PAGE_SHIFT, len >> PAGE_SHIFT);
+}
+
+static void mtd_put_device(struct super_block *sb)
+{
+	put_mtd_device(logfs_super(sb)->s_mtd);
+}
+
+static const struct logfs_device_ops mtd_devops = {
+	.find_first_sb	= mtd_find_first_sb,
+	.find_last_sb	= mtd_find_last_sb,
+	.readpage	= mtd_readpage,
+	.writeseg	= mtd_writeseg,
+	.erase		= mtd_erase,
+	.sync		= mtd_sync,
+	.put_device	= mtd_put_device,
+};
+
+int logfs_get_sb_mtd(struct file_system_type *type, int flags,
+		int mtdnr, struct vfsmount *mnt)
+{
+	struct mtd_info *mtd;
+	const struct logfs_device_ops *devops = &mtd_devops;
+
+	mtd = get_mtd_device(NULL, mtdnr);
+	return logfs_get_sb_device(type, flags, mtd, NULL, devops, mnt);
+}

fs/logfs/dir.c

···
+/*
+ * fs/logfs/dir.c	- directory-related code
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+
+
+/*
+ * Atomic dir operations
+ *
+ * Directory operations are by default not atomic.  Dentries and Inodes are
+ * created/removed/altered in seperate operations.  Therefore we need to do
+ * a small amount of journaling.
+ *
+ * Create, link, mkdir, mknod and symlink all share the same function to do
+ * the work: __logfs_create.  This function works in two atomic steps:
+ * 1. allocate inode (remember in journal)
+ * 2. allocate dentry (clear journal)
+ *
+ * As we can only get interrupted between the two, when the inode we just
+ * created is simply stored in the anchor.  On next mount, if we were
+ * interrupted, we delete the inode.  From a users point of view the
+ * operation never happened.
+ *
+ * Unlink and rmdir also share the same function: unlink.  Again, this
+ * function works in two atomic steps
+ * 1. remove dentry (remember inode in journal)
+ * 2. unlink inode (clear journal)
+ *
+ * And again, on the next mount, if we were interrupted, we delete the inode.
+ * From a users point of view the operation succeeded.
+ *
+ * Rename is the real pain to deal with, harder than all the other methods
+ * combined.  Depending on the circumstances we can run into three cases.
+ * A "target rename" where the target dentry already existed, a "local
+ * rename" where both parent directories are identical or a "cross-directory
+ * rename" in the remaining case.
+ *
+ * Local rename is atomic, as the old dentry is simply rewritten with a new
+ * name.
+ *
+ * Cross-directory rename works in two steps, similar to __logfs_create and
+ * logfs_unlink:
+ * 1. Write new dentry (remember old dentry in journal)
+ * 2. Remove old dentry (clear journal)
+ *
+ * Here we remember a dentry instead of an inode.  On next mount, if we were
+ * interrupted, we delete the dentry.  From a users point of view, the
+ * operation succeeded.
+ *
+ * Target rename works in three atomic steps:
+ * 1. Attach old inode to new dentry (remember old dentry and new inode)
+ * 2. Remove old dentry (still remember the new inode)
+ * 3. Remove victim inode
+ *
+ * Here we remember both an inode an a dentry.  If we get interrupted
+ * between steps 1 and 2, we delete both the dentry and the inode.  If
+ * we get interrupted between steps 2 and 3, we delete just the inode.
+ * In either case, the remaining objects are deleted on next mount.  From
+ * a users point of view, the operation succeeded.
+ */
+
+static int write_dir(struct inode *dir, struct logfs_disk_dentry *dd,
+		loff_t pos)
+{
+	return logfs_inode_write(dir, dd, sizeof(*dd), pos, WF_LOCK, NULL);
+}
+
+static int write_inode(struct inode *inode)
+{
+	return __logfs_write_inode(inode, WF_LOCK);
+}
+
+static s64 dir_seek_data(struct inode *inode, s64 pos)
+{
+	s64 new_pos = logfs_seek_data(inode, pos);
+
+	return max(pos, new_pos - 1);
+}
+
+static int beyond_eof(struct inode *inode, loff_t bix)
+{
+	loff_t pos = bix << inode->i_sb->s_blocksize_bits;
+	return pos >= i_size_read(inode);
+}
+
+/*
+ * Prime value was chosen to be roughly 256 + 26.  r5 hash uses 11,
+ * so short names (len <= 9) don't even occupy the complete 32bit name
+ * space.  A prime >256 ensures short names quickly spread the 32bit
+ * name space.  Add about 26 for the estimated amount of information
+ * of each character and pick a prime nearby, preferrably a bit-sparse
+ * one.
+ */
+static u32 hash_32(const char *s, int len, u32 seed)
+{
+	u32 hash = seed;
+	int i;
+
+	for (i = 0; i < len; i++)
+		hash = hash * 293 + s[i];
+	return hash;
+}
+
+/*
+ * We have to satisfy several conflicting requirements here.  Small
+ * directories should stay fairly compact and not require too many
+ * indirect blocks.  The number of possible locations for a given hash
+ * should be small to make lookup() fast.  And we should try hard not
+ * to overflow the 32bit name space or nfs and 32bit host systems will
+ * be unhappy.
+ *
+ * So we use the following scheme.  First we reduce the hash to 0..15
+ * and try a direct block.  If that is occupied we reduce the hash to
+ * 16..255 and try an indirect block.  Same for 2x and 3x indirect
+ * blocks.  Lastly we reduce the hash to 0x800_0000 .. 0xffff_ffff,
+ * but use buckets containing eight entries instead of a single one.
+ *
+ * Using 16 entries should allow for a reasonable amount of hash
+ * collisions, so the 32bit name space can be packed fairly tight
+ * before overflowing.  Oh and currently we don't overflow but return
+ * and error.
+ *
+ * How likely are collisions?  Doing the appropriate math is beyond me
+ * and the Bronstein textbook.  But running a test program to brute
+ * force collisions for a couple of days showed that on average the
+ * first collision occurs after 598M entries, with 290M being the
+ * smallest result.  Obviously 21 entries could already cause a
+ * collision if all entries are carefully chosen.
+ */
+static pgoff_t hash_index(u32 hash, int round)
+{
+	switch (round) {
+	case 0:
+		return hash % I0_BLOCKS;
+	case 1:
+		return I0_BLOCKS + hash % (I1_BLOCKS - I0_BLOCKS);
+	case 2:
+		return I1_BLOCKS + hash % (I2_BLOCKS - I1_BLOCKS);
+	case 3:
+		return I2_BLOCKS + hash % (I3_BLOCKS - I2_BLOCKS);
+	case 4 ... 19:
+		return I3_BLOCKS + 16 * (hash % (((1<<31) - I3_BLOCKS) / 16))
+			+ round - 4;
+	}
+	BUG();
+}
+
+static struct page *logfs_get_dd_page(struct inode *dir, struct dentry *dentry)
+{
+	struct qstr *name = &dentry->d_name;
+	struct page *page;
+	struct logfs_disk_dentry *dd;
+	u32 hash = hash_32(name->name, name->len, 0);
+	pgoff_t index;
+	int round;
+
+	if (name->len > LOGFS_MAX_NAMELEN)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	for (round = 0; round < 20; round++) {
+		index = hash_index(hash, round);
+
+		if (beyond_eof(dir, index))
+			return NULL;
+		if (!logfs_exist_block(dir, index))
+			continue;
+		page = read_cache_page(dir->i_mapping, index,
+				(filler_t *)logfs_readpage, NULL);
+		if (IS_ERR(page))
+			return page;
+		dd = kmap_atomic(page, KM_USER0);
+		BUG_ON(dd->namelen == 0);
+
+		if (name->len != be16_to_cpu(dd->namelen) ||
+				memcmp(name->name, dd->name, name->len)) {
+			kunmap_atomic(dd, KM_USER0);
+			page_cache_release(page);
+			continue;
+		}
+
+		kunmap_atomic(dd, KM_USER0);
+		return page;
+	}
+	return NULL;
+}
+
+static int logfs_remove_inode(struct inode *inode)
+{
+	int ret;
+
+	inode->i_nlink--;
+	ret = write_inode(inode);
+	LOGFS_BUG_ON(ret, inode->i_sb);
+	return ret;
+}
+
+static void abort_transaction(struct inode *inode, struct logfs_transaction *ta)
+{
+	if (logfs_inode(inode)->li_block)
+		logfs_inode(inode)->li_block->ta = NULL;
+	kfree(ta);
+}
+
+static int logfs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct logfs_super *super = logfs_super(dir->i_sb);
+	struct inode *inode = dentry->d_inode;
+	struct logfs_transaction *ta;
+	struct page *page;
+	pgoff_t index;
+	int ret;
+
+	ta = kzalloc(sizeof(*ta), GFP_KERNEL);
+	if (!ta)
+		return -ENOMEM;
+
+	ta->state = UNLINK_1;
+	ta->ino = inode->i_ino;
+
+	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
+
+	page = logfs_get_dd_page(dir, dentry);
+	if (!page)
+		return -ENOENT;
+	if (IS_ERR(page))
+		return PTR_ERR(page);
+	index = page->index;
+	page_cache_release(page);
+
+	mutex_lock(&super->s_dirop_mutex);
+	logfs_add_transaction(dir, ta);
+
+	ret = logfs_delete(dir, index, NULL);
+	if (!ret)
+		ret = write_inode(dir);
+
+	if (ret) {
+		abort_transaction(dir, ta);
+		printk(KERN_ERR"LOGFS: unable to delete inode\n");
+		goto out;
+	}
+
+	ta->state = UNLINK_2;
+	logfs_add_transaction(inode, ta);
+	ret = logfs_remove_inode(inode);
+out:
+	mutex_unlock(&super->s_dirop_mutex);
+	return ret;
+}
+
+static inline int logfs_empty_dir(struct inode *dir)
+{
+	u64 data;
+
+	data = logfs_seek_data(dir, 0) << dir->i_sb->s_blocksize_bits;
+	return data >= i_size_read(dir);
+}
+
+static int logfs_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+
+	if (!logfs_empty_dir(inode))
+		return -ENOTEMPTY;
+
+	return logfs_unlink(dir, dentry);
+}
+
+/* FIXME: readdir currently has it's own dir_walk code.  I don't see a good
+ * way to combine the two copies */
+#define IMPLICIT_NODES 2
+static int __logfs_readdir(struct file *file, void *buf, filldir_t filldir)
+{
+	struct inode *dir = file->f_dentry->d_inode;
+	loff_t pos = file->f_pos - IMPLICIT_NODES;
+	struct page *page;
+	struct logfs_disk_dentry *dd;
+	int full;
+
+	BUG_ON(pos < 0);
+	for (;; pos++) {
+		if (beyond_eof(dir, pos))
+			break;
+		if (!logfs_exist_block(dir, pos)) {
+			/* deleted dentry */
+			pos = dir_seek_data(dir, pos);
+			continue;
+		}
+		page = read_cache_page(dir->i_mapping, pos,
+				(filler_t *)logfs_readpage, NULL);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+		dd = kmap_atomic(page, KM_USER0);
+		BUG_ON(dd->namelen == 0);
+
+		full = filldir(buf, (char *)dd->name, be16_to_cpu(dd->namelen),
+				pos, be64_to_cpu(dd->ino), dd->type);
+		kunmap_atomic(dd, KM_USER0);
+		page_cache_release(page);
+		if (full)
+			break;
+	}
+
+	file->f_pos = pos + IMPLICIT_NODES;
+	return 0;
+}
+
+static int logfs_readdir(struct file *file, void *buf, filldir_t filldir)
+{
+	struct inode *inode = file->f_dentry->d_inode;
+	ino_t pino = parent_ino(file->f_dentry);
+	int err;
+
+	if (file->f_pos < 0)
+		return -EINVAL;
+
+	if (file->f_pos == 0) {
+		if (filldir(buf, ".", 1, 1, inode->i_ino, DT_DIR) < 0)
+			return 0;
+		file->f_pos++;
+	}
+	if (file->f_pos == 1) {
+		if (filldir(buf, "..", 2, 2, pino, DT_DIR) < 0)
+			return 0;
+		file->f_pos++;
+	}
+
+	err = __logfs_readdir(file, buf, filldir);
+	return err;
+}
+
+static void logfs_set_name(struct logfs_disk_dentry *dd, struct qstr *name)
+{
+	dd->namelen = cpu_to_be16(name->len);
+	memcpy(dd->name, name->name, name->len);
+}
+
+static struct dentry *logfs_lookup(struct inode *dir, struct dentry *dentry,
+		struct nameidata *nd)
+{
+	struct page *page;
+	struct logfs_disk_dentry *dd;
+	pgoff_t index;
+	u64 ino = 0;
+	struct inode *inode;
+
+	page = logfs_get_dd_page(dir, dentry);
+	if (IS_ERR(page))
+		return ERR_CAST(page);
+	if (!page) {
+		d_add(dentry, NULL);
+		return NULL;
+	}
+	index = page->index;
+	dd = kmap_atomic(page, KM_USER0);
+	ino = be64_to_cpu(dd->ino);
+	kunmap_atomic(dd, KM_USER0);
+	page_cache_release(page);
+
+	inode = logfs_iget(dir->i_sb, ino);
+	if (IS_ERR(inode)) {
+		printk(KERN_ERR"LogFS: Cannot read inode #%llx for dentry (%lx, %lx)n",
+				ino, dir->i_ino, index);
+		return ERR_CAST(inode);
+	}
+	return d_splice_alias(inode, dentry);
+}
+
+static void grow_dir(struct inode *dir, loff_t index)
+{
+	index = (index + 1) << dir->i_sb->s_blocksize_bits;
+	if (i_size_read(dir) < index)
+		i_size_write(dir, index);
+}
+
+static int logfs_write_dir(struct inode *dir, struct dentry *dentry,
+		struct inode *inode)
+{
+	struct page *page;
+	struct logfs_disk_dentry *dd;
+	u32 hash = hash_32(dentry->d_name.name, dentry->d_name.len, 0);
+	pgoff_t index;
+	int round, err;
+
+	for (round = 0; round < 20; round++) {
+		index = hash_index(hash, round);
+
+		if (logfs_exist_block(dir, index))
+			continue;
+		page = find_or_create_page(dir->i_mapping, index, GFP_KERNEL);
+		if (!page)
+			return -ENOMEM;
+
+		dd = kmap_atomic(page, KM_USER0);
+		memset(dd, 0, sizeof(*dd));
+		dd->ino = cpu_to_be64(inode->i_ino);
+		dd->type = logfs_type(inode);
+		logfs_set_name(dd, &dentry->d_name);
+		kunmap_atomic(dd, KM_USER0);
+
+		err = logfs_write_buf(dir, page, WF_LOCK);
+		unlock_page(page);
+		page_cache_release(page);
+		if (!err)
+			grow_dir(dir, index);
+		return err;
+	}
+	/* FIXME: Is there a better return value?  In most cases neither
+	 * the filesystem nor the directory are full.  But we have had
+	 * too many collisions for this particular hash and no fallback.
+	 */
+	return -ENOSPC;
+}
+
+static int __logfs_create(struct inode *dir, struct dentry *dentry,
+		struct inode *inode, const char *dest, long destlen)
+{
+	struct logfs_super *super = logfs_super(dir->i_sb);
+	struct logfs_inode *li = logfs_inode(inode);
+	struct logfs_transaction *ta;
+	int ret;
+
+	ta = kzalloc(sizeof(*ta), GFP_KERNEL);
+	if (!ta)
+		return -ENOMEM;
+
+	ta->state = CREATE_1;
+	ta->ino = inode->i_ino;
+	mutex_lock(&super->s_dirop_mutex);
+	logfs_add_transaction(inode, ta);
+
+	if (dest) {
+		/* symlink */
+		ret = logfs_inode_write(inode, dest, destlen, 0, WF_LOCK, NULL);
+		if (!ret)
+			ret = write_inode(inode);
+	} else {
+		/* creat/mkdir/mknod */
+		ret = write_inode(inode);
+	}
+	if (ret) {
+		abort_transaction(inode, ta);
+		li->li_flags |= LOGFS_IF_STILLBORN;
+		/* FIXME: truncate symlink */
+		inode->i_nlink--;
+		iput(inode);
+		goto out;
+	}
+
+	ta->state = CREATE_2;
+	logfs_add_transaction(dir, ta);
+	ret = logfs_write_dir(dir, dentry, inode);
+	/* sync directory */
+	if (!ret)
+		ret = write_inode(dir);
+
+	if (ret) {
+		logfs_del_transaction(dir, ta);
+		ta->state = CREATE_2;
+		logfs_add_transaction(inode, ta);
+		logfs_remove_inode(inode);
+		iput(inode);
+		goto out;
+	}
+	d_instantiate(dentry, inode);
+out:
+	mutex_unlock(&super->s_dirop_mutex);
+	return ret;
+}
+
+static int logfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+{
+	struct inode *inode;
+
+	/*
+	 * FIXME: why do we have to fill in S_IFDIR, while the mode is
+	 * correct for mknod, creat, etc.?  Smells like the vfs *should*
+	 * do it for us but for some reason fails to do so.
+	 */
+	inode = logfs_new_inode(dir, S_IFDIR | mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	inode->i_op = &logfs_dir_iops;
+	inode->i_fop = &logfs_dir_fops;
+
+	return __logfs_create(dir, dentry, inode, NULL, 0);
+}
+
+static int logfs_create(struct inode *dir, struct dentry *dentry, int mode,
+		struct nameidata *nd)
+{
+	struct inode *inode;
+
+	inode = logfs_new_inode(dir, mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	inode->i_op = &logfs_reg_iops;
+	inode->i_fop = &logfs_reg_fops;
+	inode->i_mapping->a_ops = &logfs_reg_aops;
+
+	return __logfs_create(dir, dentry, inode, NULL, 0);
+}
+
+static int logfs_mknod(struct inode *dir, struct dentry *dentry, int mode,
+		dev_t rdev)
+{
+	struct inode *inode;
+
+	if (dentry->d_name.len > LOGFS_MAX_NAMELEN)
+		return -ENAMETOOLONG;
+
+	inode = logfs_new_inode(dir, mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	init_special_inode(inode, mode, rdev);
+
+	return __logfs_create(dir, dentry, inode, NULL, 0);
+}
+
+static int logfs_symlink(struct inode *dir, struct dentry *dentry,
+		const char *target)
+{
+	struct inode *inode;
+	size_t destlen = strlen(target) + 1;
+
+	if (destlen > dir->i_sb->s_blocksize)
+		return -ENAMETOOLONG;
+
+	inode = logfs_new_inode(dir, S_IFLNK | 0777);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	inode->i_op = &logfs_symlink_iops;
+	inode->i_mapping->a_ops = &logfs_reg_aops;
+
+	return __logfs_create(dir, dentry, inode, target, destlen);
+}
+
+static int logfs_permission(struct inode *inode, int mask)
+{
+	return generic_permission(inode, mask, NULL);
+}
+
+static int logfs_link(struct dentry *old_dentry, struct inode *dir,
+		struct dentry *dentry)
+{
+	struct inode *inode = old_dentry->d_inode;
+
+	if (inode->i_nlink >= LOGFS_LINK_MAX)
+		return -EMLINK;
+
+	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
+	atomic_inc(&inode->i_count);
+	inode->i_nlink++;
+	mark_inode_dirty_sync(inode);
+
+	return __logfs_create(dir, dentry, inode, NULL, 0);
+}
+
+static int logfs_get_dd(struct inode *dir, struct dentry *dentry,
+		struct logfs_disk_dentry *dd, loff_t *pos)
+{
+	struct page *page;
+	void *map;
+
+	page = logfs_get_dd_page(dir, dentry);
+	if (IS_ERR(page))
+		return PTR_ERR(page);
+	*pos = page->index;
+	map = kmap_atomic(page, KM_USER0);
+	memcpy(dd, map, sizeof(*dd));
+	kunmap_atomic(map, KM_USER0);
+	page_cache_release(page);
+	return 0;
+}
+
+static int logfs_delete_dd(struct inode *dir, loff_t pos)
+{
+	/*
+	 * Getting called with pos somewhere beyond eof is either a goofup
+	 * within this file or means someone maliciously edited the
+	 * (crc-protected) journal.
+	 */
+	BUG_ON(beyond_eof(dir, pos));
+	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
+	log_dir(" Delete dentry (%lx, %llx)\n", dir->i_ino, pos);
+	return logfs_delete(dir, pos, NULL);
+}
+
+/*
+ * Cross-directory rename, target does not exist.  Just a little nasty.
+ * Create a new dentry in the target dir, then remove the old dentry,
+ * all the while taking care to remember our operation in the journal.
+ */
+static int logfs_rename_cross(struct inode *old_dir, struct dentry *old_dentry,
+			      struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct logfs_super *super = logfs_super(old_dir->i_sb);
+	struct logfs_disk_dentry dd;
+	struct logfs_transaction *ta;
+	loff_t pos;
+	int err;
+
+	/* 1. locate source dd */
+	err = logfs_get_dd(old_dir, old_dentry, &dd, &pos);
+	if (err)
+		return err;
+
+	ta = kzalloc(sizeof(*ta), GFP_KERNEL);
+	if (!ta)
+		return -ENOMEM;
+
+	ta->state = CROSS_RENAME_1;
+	ta->dir = old_dir->i_ino;
+	ta->pos = pos;
+
+	/* 2. write target dd */
+	mutex_lock(&super->s_dirop_mutex);
+	logfs_add_transaction(new_dir, ta);
+	err = logfs_write_dir(new_dir, new_dentry, old_dentry->d_inode);
+	if (!err)
+		err = write_inode(new_dir);
+
+	if (err) {
+		super->s_rename_dir = 0;
+		super->s_rename_pos = 0;
+		abort_transaction(new_dir, ta);
+		goto out;
+	}
+
+	/* 3. remove source dd */
+	ta->state = CROSS_RENAME_2;
+	logfs_add_transaction(old_dir, ta);
+	err = logfs_delete_dd(old_dir, pos);
+	if (!err)
+		err = write_inode(old_dir);
+	LOGFS_BUG_ON(err, old_dir->i_sb);
+out:
+	mutex_unlock(&super->s_dirop_mutex);
+	return err;
+}
+
+static int logfs_replace_inode(struct inode *dir, struct dentry *dentry,
+		struct logfs_disk_dentry *dd, struct inode *inode)
+{
+	loff_t pos;
+	int err;
+
+	err = logfs_get_dd(dir, dentry, dd, &pos);
+	if (err)
+		return err;
+	dd->ino = cpu_to_be64(inode->i_ino);
+	dd->type = logfs_type(inode);
+
+	err = write_dir(dir, dd, pos);
+	if (err)
+		return err;
+	log_dir("Replace dentry (%lx, %llx) %s -> %llx\n", dir->i_ino, pos,
+			dd->name, be64_to_cpu(dd->ino));
+	return write_inode(dir);
+}
+
+/* Target dentry exists - the worst case.  We need to attach the source
+ * inode to the target dentry, then remove the orphaned target inode and
+ * source dentry.
+ */
+static int logfs_rename_target(struct inode *old_dir, struct dentry *old_dentry,
+			       struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct logfs_super *super = logfs_super(old_dir->i_sb);
+	struct inode *old_inode = old_dentry->d_inode;
+	struct inode *new_inode = new_dentry->d_inode;
+	int isdir = S_ISDIR(old_inode->i_mode);
+	struct logfs_disk_dentry dd;
+	struct logfs_transaction *ta;
+	loff_t pos;
+	int err;
+
+	BUG_ON(isdir != S_ISDIR(new_inode->i_mode));
+	if (isdir) {
+		if (!logfs_empty_dir(new_inode))
+			return -ENOTEMPTY;
+	}
+
+	/* 1. locate source dd */
+	err = logfs_get_dd(old_dir, old_dentry, &dd, &pos);
+	if (err)
+		return err;
+
+	ta = kzalloc(sizeof(*ta), GFP_KERNEL);
+	if (!ta)
+		return -ENOMEM;
+
+	ta->state = TARGET_RENAME_1;
+	ta->dir = old_dir->i_ino;
+	ta->pos = pos;
+	ta->ino = new_inode->i_ino;
+
+	/* 2. attach source inode to target dd */
+	mutex_lock(&super->s_dirop_mutex);
+	logfs_add_transaction(new_dir, ta);
+	err = logfs_replace_inode(new_dir, new_dentry, &dd, old_inode);
+	if (err) {
+		super->s_rename_dir = 0;
+		super->s_rename_pos = 0;
+		super->s_victim_ino = 0;
+		abort_transaction(new_dir, ta);
+		goto out;
+	}
+
+	/* 3. remove source dd */
+	ta->state = TARGET_RENAME_2;
+	logfs_add_transaction(old_dir, ta);
+	err = logfs_delete_dd(old_dir, pos);
+	if (!err)
+		err = write_inode(old_dir);
+	LOGFS_BUG_ON(err, old_dir->i_sb);
+
+	/* 4. remove target inode */
+	ta->state = TARGET_RENAME_3;
+	logfs_add_transaction(new_inode, ta);
+	err = logfs_remove_inode(new_inode);
+
+out:
+	mutex_unlock(&super->s_dirop_mutex);
+	return err;
+}
+
+static int logfs_rename(struct inode *old_dir, struct dentry *old_dentry,
+			struct inode *new_dir, struct dentry *new_dentry)
+{
+	if (new_dentry->d_inode)
+		return logfs_rename_target(old_dir, old_dentry,
+					   new_dir, new_dentry);
+	return logfs_rename_cross(old_dir, old_dentry, new_dir, new_dentry);
+}
+
+/* No locking done here, as this is called before .get_sb() returns. */
+int logfs_replay_journal(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode;
+	u64 ino, pos;
+	int err;
+
+	if (super->s_victim_ino) {
+		/* delete victim inode */
+		ino = super->s_victim_ino;
+		printk(KERN_INFO"LogFS: delete unmapped inode #%llx\n", ino);
+		inode = logfs_iget(sb, ino);
+		if (IS_ERR(inode))
+			goto fail;
+
+		LOGFS_BUG_ON(i_size_read(inode) > 0, sb);
+		super->s_victim_ino = 0;
+		err = logfs_remove_inode(inode);
+		iput(inode);
+		if (err) {
+			super->s_victim_ino = ino;
+			goto fail;
+		}
+	}
+	if (super->s_rename_dir) {
+		/* delete old dd from rename */
+		ino = super->s_rename_dir;
+		pos = super->s_rename_pos;
+		printk(KERN_INFO"LogFS: delete unbacked dentry (%llx, %llx)\n",
+				ino, pos);
+		inode = logfs_iget(sb, ino);
+		if (IS_ERR(inode))
+			goto fail;
+
+		super->s_rename_dir = 0;
+		super->s_rename_pos = 0;
+		err = logfs_delete_dd(inode, pos);
+		iput(inode);
+		if (err) {
+			super->s_rename_dir = ino;
+			super->s_rename_pos = pos;
+			goto fail;
+		}
+	}
+	return 0;
+fail:
+	LOGFS_BUG(sb);
+	return -EIO;
+}
+
+const struct inode_operations logfs_symlink_iops = {
+	.readlink	= generic_readlink,
+	.follow_link	= page_follow_link_light,
+};
+
+const struct inode_operations logfs_dir_iops = {
+	.create		= logfs_create,
+	.link		= logfs_link,
+	.lookup		= logfs_lookup,
+	.mkdir		= logfs_mkdir,
+	.mknod		= logfs_mknod,
+	.rename		= logfs_rename,
+	.rmdir		= logfs_rmdir,
+	.permission	= logfs_permission,
+	.symlink	= logfs_symlink,
+	.unlink		= logfs_unlink,
+};
+const struct file_operations logfs_dir_fops = {
+	.fsync		= logfs_fsync,
+	.ioctl		= logfs_ioctl,
+	.readdir	= logfs_readdir,
+	.read		= generic_read_dir,
+};

fs/logfs/file.c

···
+/*
+ * fs/logfs/file.c	- prepare_write, commit_write and friends
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/sched.h>
+#include <linux/writeback.h>
+
+static int logfs_write_begin(struct file *file, struct address_space *mapping,
+		loff_t pos, unsigned len, unsigned flags,
+		struct page **pagep, void **fsdata)
+{
+	struct inode *inode = mapping->host;
+	struct page *page;
+	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
+
+	page = grab_cache_page_write_begin(mapping, index, flags);
+	if (!page)
+		return -ENOMEM;
+	*pagep = page;
+
+	if ((len == PAGE_CACHE_SIZE) || PageUptodate(page))
+		return 0;
+	if ((pos & PAGE_CACHE_MASK) >= i_size_read(inode)) {
+		unsigned start = pos & (PAGE_CACHE_SIZE - 1);
+		unsigned end = start + len;
+
+		/* Reading beyond i_size is simple: memset to zero */
+		zero_user_segments(page, 0, start, end, PAGE_CACHE_SIZE);
+		return 0;
+	}
+	return logfs_readpage_nolock(page);
+}
+
+static int logfs_write_end(struct file *file, struct address_space *mapping,
+		loff_t pos, unsigned len, unsigned copied, struct page *page,
+		void *fsdata)
+{
+	struct inode *inode = mapping->host;
+	pgoff_t index = page->index;
+	unsigned start = pos & (PAGE_CACHE_SIZE - 1);
+	unsigned end = start + copied;
+	int ret = 0;
+
+	BUG_ON(PAGE_CACHE_SIZE != inode->i_sb->s_blocksize);
+	BUG_ON(page->index > I3_BLOCKS);
+
+	if (copied < len) {
+		/*
+		 * Short write of a non-initialized paged.  Just tell userspace
+		 * to retry the entire page.
+		 */
+		if (!PageUptodate(page)) {
+			copied = 0;
+			goto out;
+		}
+	}
+	if (copied == 0)
+		goto out; /* FIXME: do we need to update inode? */
+
+	if (i_size_read(inode) < (index << PAGE_CACHE_SHIFT) + end) {
+		i_size_write(inode, (index << PAGE_CACHE_SHIFT) + end);
+		mark_inode_dirty_sync(inode);
+	}
+
+	SetPageUptodate(page);
+	if (!PageDirty(page)) {
+		if (!get_page_reserve(inode, page))
+			__set_page_dirty_nobuffers(page);
+		else
+			ret = logfs_write_buf(inode, page, WF_LOCK);
+	}
+out:
+	unlock_page(page);
+	page_cache_release(page);
+	return ret ? ret : copied;
+}
+
+int logfs_readpage(struct file *file, struct page *page)
+{
+	int ret;
+
+	ret = logfs_readpage_nolock(page);
+	unlock_page(page);
+	return ret;
+}
+
+/* Clear the page's dirty flag in the radix tree. */
+/* TODO: mucking with PageWriteback is silly.  Add a generic function to clear
+ * the dirty bit from the radix tree for filesystems that don't have to wait
+ * for page writeback to finish (i.e. any compressing filesystem).
+ */
+static void clear_radix_tree_dirty(struct page *page)
+{
+	BUG_ON(PagePrivate(page) || page->private);
+	set_page_writeback(page);
+	end_page_writeback(page);
+}
+
+static int __logfs_writepage(struct page *page)
+{
+	struct inode *inode = page->mapping->host;
+	int err;
+
+	err = logfs_write_buf(inode, page, WF_LOCK);
+	if (err)
+		set_page_dirty(page);
+	else
+		clear_radix_tree_dirty(page);
+	unlock_page(page);
+	return err;
+}
+
+static int logfs_writepage(struct page *page, struct writeback_control *wbc)
+{
+	struct inode *inode = page->mapping->host;
+	loff_t i_size = i_size_read(inode);
+	pgoff_t end_index = i_size >> PAGE_CACHE_SHIFT;
+	unsigned offset;
+	u64 bix;
+	level_t level;
+
+	log_file("logfs_writepage(%lx, %lx, %p)\n", inode->i_ino, page->index,
+			page);
+
+	logfs_unpack_index(page->index, &bix, &level);
+
+	/* Indirect blocks are never truncated */
+	if (level != 0)
+		return __logfs_writepage(page);
+
+	/*
+	 * TODO: everything below is a near-verbatim copy of nobh_writepage().
+	 * The relevant bits should be factored out after logfs is merged.
+	 */
+
+	/* Is the page fully inside i_size? */
+	if (bix < end_index)
+		return __logfs_writepage(page);
+
+	 /* Is the page fully outside i_size? (truncate in progress) */
+	offset = i_size & (PAGE_CACHE_SIZE-1);
+	if (bix > end_index || offset == 0) {
+		unlock_page(page);
+		return 0; /* don't care */
+	}
+
+	/*
+	 * The page straddles i_size.  It must be zeroed out on each and every
+	 * writepage invokation because it may be mmapped.  "A file is mapped
+	 * in multiples of the page size.  For a file that is not a multiple of
+	 * the  page size, the remaining memory is zeroed when mapped, and
+	 * writes to that region are not written out to the file."
+	 */
+	zero_user_segment(page, offset, PAGE_CACHE_SIZE);
+	return __logfs_writepage(page);
+}
+
+static void logfs_invalidatepage(struct page *page, unsigned long offset)
+{
+	move_page_to_btree(page);
+	BUG_ON(PagePrivate(page) || page->private);
+}
+
+static int logfs_releasepage(struct page *page, gfp_t only_xfs_uses_this)
+{
+	return 0; /* None of these are easy to release */
+}
+
+
+int logfs_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
+		unsigned long arg)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	unsigned int oldflags, flags;
+	int err;
+
+	switch (cmd) {
+	case FS_IOC_GETFLAGS:
+		flags = li->li_flags & LOGFS_FL_USER_VISIBLE;
+		return put_user(flags, (int __user *)arg);
+	case FS_IOC_SETFLAGS:
+		if (IS_RDONLY(inode))
+			return -EROFS;
+
+		if (!is_owner_or_cap(inode))
+			return -EACCES;
+
+		err = get_user(flags, (int __user *)arg);
+		if (err)
+			return err;
+
+		mutex_lock(&inode->i_mutex);
+		oldflags = li->li_flags;
+		flags &= LOGFS_FL_USER_MODIFIABLE;
+		flags |= oldflags & ~LOGFS_FL_USER_MODIFIABLE;
+		li->li_flags = flags;
+		mutex_unlock(&inode->i_mutex);
+
+		inode->i_ctime = CURRENT_TIME;
+		mark_inode_dirty_sync(inode);
+		return 0;
+
+	default:
+		return -ENOTTY;
+	}
+}
+
+int logfs_fsync(struct file *file, struct dentry *dentry, int datasync)
+{
+	struct super_block *sb = dentry->d_inode->i_sb;
+	struct logfs_super *super = logfs_super(sb);
+
+	/* FIXME: write anchor */
+	super->s_devops->sync(sb);
+	return 0;
+}
+
+static int logfs_setattr(struct dentry *dentry, struct iattr *attr)
+{
+	struct inode *inode = dentry->d_inode;
+	int err = 0;
+
+	if (attr->ia_valid & ATTR_SIZE)
+		err = logfs_truncate(inode, attr->ia_size);
+	attr->ia_valid &= ~ATTR_SIZE;
+
+	if (!err)
+		err = inode_change_ok(inode, attr);
+	if (!err)
+		err = inode_setattr(inode, attr);
+	return err;
+}
+
+const struct inode_operations logfs_reg_iops = {
+	.setattr	= logfs_setattr,
+};
+
+const struct file_operations logfs_reg_fops = {
+	.aio_read	= generic_file_aio_read,
+	.aio_write	= generic_file_aio_write,
+	.fsync		= logfs_fsync,
+	.ioctl		= logfs_ioctl,
+	.llseek		= generic_file_llseek,
+	.mmap		= generic_file_readonly_mmap,
+	.open		= generic_file_open,
+	.read		= do_sync_read,
+	.write		= do_sync_write,
+};
+
+const struct address_space_operations logfs_reg_aops = {
+	.invalidatepage	= logfs_invalidatepage,
+	.readpage	= logfs_readpage,
+	.releasepage	= logfs_releasepage,
+	.set_page_dirty	= __set_page_dirty_nobuffers,
+	.writepage	= logfs_writepage,
+	.writepages	= generic_writepages,
+	.write_begin	= logfs_write_begin,
+	.write_end	= logfs_write_end,
+};

fs/logfs/gc.c

···
+/*
+ * fs/logfs/gc.c	- garbage collection code
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/sched.h>
+
+/*
+ * Wear leveling needs to kick in when the difference between low erase
+ * counts and high erase counts gets too big.  A good value for "too big"
+ * may be somewhat below 10% of maximum erase count for the device.
+ * Why not 397, to pick a nice round number with no specific meaning? :)
+ *
+ * WL_RATELIMIT is the minimum time between two wear level events.  A huge
+ * number of segments may fulfil the requirements for wear leveling at the
+ * same time.  If that happens we don't want to cause a latency from hell,
+ * but just gently pick one segment every so often and minimize overhead.
+ */
+#define WL_DELTA 397
+#define WL_RATELIMIT 100
+#define MAX_OBJ_ALIASES	2600
+#define SCAN_RATIO 512	/* number of scanned segments per gc'd segment */
+#define LIST_SIZE 64	/* base size of candidate lists */
+#define SCAN_ROUNDS 128	/* maximum number of complete medium scans */
+#define SCAN_ROUNDS_HIGH 4 /* maximum number of higher-level scans */
+
+static int no_free_segments(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	return super->s_free_list.count;
+}
+
+/* journal has distance -1, top-most ifile layer distance 0 */
+static u8 root_distance(struct super_block *sb, gc_level_t __gc_level)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u8 gc_level = (__force u8)__gc_level;
+
+	switch (gc_level) {
+	case 0: /* fall through */
+	case 1: /* fall through */
+	case 2: /* fall through */
+	case 3:
+		/* file data or indirect blocks */
+		return super->s_ifile_levels + super->s_iblock_levels - gc_level;
+	case 6: /* fall through */
+	case 7: /* fall through */
+	case 8: /* fall through */
+	case 9:
+		/* inode file data or indirect blocks */
+		return super->s_ifile_levels - (gc_level - 6);
+	default:
+		printk(KERN_ERR"LOGFS: segment of unknown level %x found\n",
+				gc_level);
+		WARN_ON(1);
+		return super->s_ifile_levels + super->s_iblock_levels;
+	}
+}
+
+static int segment_is_reserved(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area;
+	void *reserved;
+	int i;
+
+	/* Some segments are reserved.  Just pretend they were all valid */
+	reserved = btree_lookup32(&super->s_reserved_segments, segno);
+	if (reserved)
+		return 1;
+
+	/* Currently open segments */
+	for_each_area(i) {
+		area = super->s_area[i];
+		if (area->a_is_open && area->a_segno == segno)
+			return 1;
+	}
+
+	return 0;
+}
+
+static void logfs_mark_segment_bad(struct super_block *sb, u32 segno)
+{
+	BUG();
+}
+
+/*
+ * Returns the bytes consumed by valid objects in this segment.  Object headers
+ * are counted, the segment header is not.
+ */
+static u32 logfs_valid_bytes(struct super_block *sb, u32 segno, u32 *ec,
+		gc_level_t *gc_level)
+{
+	struct logfs_segment_entry se;
+	u32 ec_level;
+
+	logfs_get_segment_entry(sb, segno, &se);
+	if (se.ec_level == cpu_to_be32(BADSEG) ||
+			se.valid == cpu_to_be32(RESERVED))
+		return RESERVED;
+
+	ec_level = be32_to_cpu(se.ec_level);
+	*ec = ec_level >> 4;
+	*gc_level = GC_LEVEL(ec_level & 0xf);
+	return be32_to_cpu(se.valid);
+}
+
+static void logfs_cleanse_block(struct super_block *sb, u64 ofs, u64 ino,
+		u64 bix, gc_level_t gc_level)
+{
+	struct inode *inode;
+	int err, cookie;
+
+	inode = logfs_safe_iget(sb, ino, &cookie);
+	err = logfs_rewrite_block(inode, bix, ofs, gc_level, 0);
+	BUG_ON(err);
+	logfs_safe_iput(inode, cookie);
+}
+
+static u32 logfs_gc_segment(struct super_block *sb, u32 segno, u8 dist)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_segment_header sh;
+	struct logfs_object_header oh;
+	u64 ofs, ino, bix;
+	u32 seg_ofs, logical_segno, cleaned = 0;
+	int err, len, valid;
+	gc_level_t gc_level;
+
+	LOGFS_BUG_ON(segment_is_reserved(sb, segno), sb);
+
+	btree_insert32(&super->s_reserved_segments, segno, (void *)1, GFP_NOFS);
+	err = wbuf_read(sb, dev_ofs(sb, segno, 0), sizeof(sh), &sh);
+	BUG_ON(err);
+	gc_level = GC_LEVEL(sh.level);
+	logical_segno = be32_to_cpu(sh.segno);
+	if (sh.crc != logfs_crc32(&sh, sizeof(sh), 4)) {
+		logfs_mark_segment_bad(sb, segno);
+		cleaned = -1;
+		goto out;
+	}
+
+	for (seg_ofs = LOGFS_SEGMENT_HEADERSIZE;
+			seg_ofs + sizeof(oh) < super->s_segsize; ) {
+		ofs = dev_ofs(sb, logical_segno, seg_ofs);
+		err = wbuf_read(sb, dev_ofs(sb, segno, seg_ofs), sizeof(oh),
+				&oh);
+		BUG_ON(err);
+
+		if (!memchr_inv(&oh, 0xff, sizeof(oh)))
+			break;
+
+		if (oh.crc != logfs_crc32(&oh, sizeof(oh) - 4, 4)) {
+			logfs_mark_segment_bad(sb, segno);
+			cleaned = super->s_segsize - 1;
+			goto out;
+		}
+
+		ino = be64_to_cpu(oh.ino);
+		bix = be64_to_cpu(oh.bix);
+		len = sizeof(oh) + be16_to_cpu(oh.len);
+		valid = logfs_is_valid_block(sb, ofs, ino, bix, gc_level);
+		if (valid == 1) {
+			logfs_cleanse_block(sb, ofs, ino, bix, gc_level);
+			cleaned += len;
+		} else if (valid == 2) {
+			/* Will be invalid upon journal commit */
+			cleaned += len;
+		}
+		seg_ofs += len;
+	}
+out:
+	btree_remove32(&super->s_reserved_segments, segno);
+	return cleaned;
+}
+
+static struct gc_candidate *add_list(struct gc_candidate *cand,
+		struct candidate_list *list)
+{
+	struct rb_node **p = &list->rb_tree.rb_node;
+	struct rb_node *parent = NULL;
+	struct gc_candidate *cur;
+	int comp;
+
+	cand->list = list;
+	while (*p) {
+		parent = *p;
+		cur = rb_entry(parent, struct gc_candidate, rb_node);
+
+		if (list->sort_by_ec)
+			comp = cand->erase_count < cur->erase_count;
+		else
+			comp = cand->valid < cur->valid;
+
+		if (comp)
+			p = &parent->rb_left;
+		else
+			p = &parent->rb_right;
+	}
+	rb_link_node(&cand->rb_node, parent, p);
+	rb_insert_color(&cand->rb_node, &list->rb_tree);
+
+	if (list->count <= list->maxcount) {
+		list->count++;
+		return NULL;
+	}
+	cand = rb_entry(rb_last(&list->rb_tree), struct gc_candidate, rb_node);
+	rb_erase(&cand->rb_node, &list->rb_tree);
+	cand->list = NULL;
+	return cand;
+}
+
+static void remove_from_list(struct gc_candidate *cand)
+{
+	struct candidate_list *list = cand->list;
+
+	rb_erase(&cand->rb_node, &list->rb_tree);
+	list->count--;
+}
+
+static void free_candidate(struct super_block *sb, struct gc_candidate *cand)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	btree_remove32(&super->s_cand_tree, cand->segno);
+	kfree(cand);
+}
+
+u32 get_best_cand(struct super_block *sb, struct candidate_list *list, u32 *ec)
+{
+	struct gc_candidate *cand;
+	u32 segno;
+
+	BUG_ON(list->count == 0);
+
+	cand = rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node);
+	remove_from_list(cand);
+	segno = cand->segno;
+	if (ec)
+		*ec = cand->erase_count;
+	free_candidate(sb, cand);
+	return segno;
+}
+
+/*
+ * We have several lists to manage segments with.  The reserve_list is used to
+ * deal with bad blocks.  We try to keep the best (lowest ec) segments on this
+ * list.
+ * The free_list contains free segments for normal usage.  It usually gets the
+ * second pick after the reserve_list.  But when the free_list is running short
+ * it is more important to keep the free_list full than to keep a reserve.
+ *
+ * Segments that are not free are put onto a per-level low_list.  If we have
+ * to run garbage collection, we pick a candidate from there.  All segments on
+ * those lists should have at least some free space so GC will make progress.
+ *
+ * And last we have the ec_list, which is used to pick segments for wear
+ * leveling.
+ *
+ * If all appropriate lists are full, we simply free the candidate and forget
+ * about that segment for a while.  We have better candidates for each purpose.
+ */
+static void __add_candidate(struct super_block *sb, struct gc_candidate *cand)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u32 full = super->s_segsize - LOGFS_SEGMENT_RESERVE;
+
+	if (cand->valid == 0) {
+		/* 100% free segments */
+		log_gc_noisy("add reserve segment %x (ec %x) at %llx\n",
+				cand->segno, cand->erase_count,
+				dev_ofs(sb, cand->segno, 0));
+		cand = add_list(cand, &super->s_reserve_list);
+		if (cand) {
+			log_gc_noisy("add free segment %x (ec %x) at %llx\n",
+					cand->segno, cand->erase_count,
+					dev_ofs(sb, cand->segno, 0));
+			cand = add_list(cand, &super->s_free_list);
+		}
+	} else {
+		/* good candidates for Garbage Collection */
+		if (cand->valid < full)
+			cand = add_list(cand, &super->s_low_list[cand->dist]);
+		/* good candidates for wear leveling,
+		 * segments that were recently written get ignored */
+		if (cand)
+			cand = add_list(cand, &super->s_ec_list);
+	}
+	if (cand)
+		free_candidate(sb, cand);
+}
+
+static int add_candidate(struct super_block *sb, u32 segno, u32 valid, u32 ec,
+		u8 dist)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct gc_candidate *cand;
+
+	cand = kmalloc(sizeof(*cand), GFP_NOFS);
+	if (!cand)
+		return -ENOMEM;
+
+	cand->segno = segno;
+	cand->valid = valid;
+	cand->erase_count = ec;
+	cand->dist = dist;
+
+	btree_insert32(&super->s_cand_tree, segno, cand, GFP_NOFS);
+	__add_candidate(sb, cand);
+	return 0;
+}
+
+static void remove_segment_from_lists(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct gc_candidate *cand;
+
+	cand = btree_lookup32(&super->s_cand_tree, segno);
+	if (cand) {
+		remove_from_list(cand);
+		free_candidate(sb, cand);
+	}
+}
+
+static void scan_segment(struct super_block *sb, u32 segno)
+{
+	u32 valid, ec = 0;
+	gc_level_t gc_level = 0;
+	u8 dist;
+
+	if (segment_is_reserved(sb, segno))
+		return;
+
+	remove_segment_from_lists(sb, segno);
+	valid = logfs_valid_bytes(sb, segno, &ec, &gc_level);
+	if (valid == RESERVED)
+		return;
+
+	dist = root_distance(sb, gc_level);
+	add_candidate(sb, segno, valid, ec, dist);
+}
+
+static struct gc_candidate *first_in_list(struct candidate_list *list)
+{
+	if (list->count == 0)
+		return NULL;
+	return rb_entry(rb_first(&list->rb_tree), struct gc_candidate, rb_node);
+}
+
+/*
+ * Find the best segment for garbage collection.  Main criterion is
+ * the segment requiring the least effort to clean.  Secondary
+ * criterion is to GC on the lowest level available.
+ *
+ * So we search the least effort segment on the lowest level first,
+ * then move up and pick another segment iff is requires significantly
+ * less effort.  Hence the LOGFS_MAX_OBJECTSIZE in the comparison.
+ */
+static struct gc_candidate *get_candidate(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i, max_dist;
+	struct gc_candidate *cand = NULL, *this;
+
+	max_dist = min(no_free_segments(sb), LOGFS_NO_AREAS);
+
+	for (i = max_dist; i >= 0; i--) {
+		this = first_in_list(&super->s_low_list[i]);
+		if (!this)
+			continue;
+		if (!cand)
+			cand = this;
+		if (this->valid + LOGFS_MAX_OBJECTSIZE <= cand->valid)
+			cand = this;
+	}
+	return cand;
+}
+
+static int __logfs_gc_once(struct super_block *sb, struct gc_candidate *cand)
+{
+	struct logfs_super *super = logfs_super(sb);
+	gc_level_t gc_level;
+	u32 cleaned, valid, segno, ec;
+	u8 dist;
+
+	if (!cand) {
+		log_gc("GC attempted, but no candidate found\n");
+		return 0;
+	}
+
+	segno = cand->segno;
+	dist = cand->dist;
+	valid = logfs_valid_bytes(sb, segno, &ec, &gc_level);
+	free_candidate(sb, cand);
+	log_gc("GC segment #%02x at %llx, %x required, %x free, %x valid, %llx free\n",
+			segno, (u64)segno << super->s_segshift,
+			dist, no_free_segments(sb), valid,
+			super->s_free_bytes);
+	cleaned = logfs_gc_segment(sb, segno, dist);
+	log_gc("GC segment #%02x complete - now %x valid\n", segno,
+			valid - cleaned);
+	BUG_ON(cleaned != valid);
+	return 1;
+}
+
+static int logfs_gc_once(struct super_block *sb)
+{
+	struct gc_candidate *cand;
+
+	cand = get_candidate(sb);
+	if (cand)
+		remove_from_list(cand);
+	return __logfs_gc_once(sb, cand);
+}
+
+/* returns 1 if a wrap occurs, 0 otherwise */
+static int logfs_scan_some(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u32 segno;
+	int i, ret = 0;
+
+	segno = super->s_sweeper;
+	for (i = SCAN_RATIO; i > 0; i--) {
+		segno++;
+		if (segno >= super->s_no_segs) {
+			segno = 0;
+			ret = 1;
+			/* Break out of the loop.  We want to read a single
+			 * block from the segment size on next invocation if
+			 * SCAN_RATIO is set to match block size
+			 */
+			break;
+		}
+
+		scan_segment(sb, segno);
+	}
+	super->s_sweeper = segno;
+	return ret;
+}
+
+/*
+ * In principle, this function should loop forever, looking for GC candidates
+ * and moving data.  LogFS is designed in such a way that this loop is
+ * guaranteed to terminate.
+ *
+ * Limiting the loop to some iterations serves purely to catch cases when
+ * these guarantees have failed.  An actual endless loop is an obvious bug
+ * and should be reported as such.
+ */
+static void __logfs_gc_pass(struct super_block *sb, int target)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_block *block;
+	int round, progress, last_progress = 0;
+
+	if (no_free_segments(sb) >= target &&
+			super->s_no_object_aliases < MAX_OBJ_ALIASES)
+		return;
+
+	log_gc("__logfs_gc_pass(%x)\n", target);
+	for (round = 0; round < SCAN_ROUNDS; ) {
+		if (no_free_segments(sb) >= target)
+			goto write_alias;
+
+		/* Sync in-memory state with on-medium state in case they
+		 * diverged */
+		logfs_write_anchor(super->s_master_inode);
+		round += logfs_scan_some(sb);
+		if (no_free_segments(sb) >= target)
+			goto write_alias;
+		progress = logfs_gc_once(sb);
+		if (progress)
+			last_progress = round;
+		else if (round - last_progress > 2)
+			break;
+		continue;
+
+		/*
+		 * The goto logic is nasty, I just don't know a better way to
+		 * code it.  GC is supposed to ensure two things:
+		 * 1. Enough free segments are available.
+		 * 2. The number of aliases is bounded.
+		 * When 1. is achieved, we take a look at 2. and write back
+		 * some alias-containing blocks, if necessary.  However, after
+		 * each such write we need to go back to 1., as writes can
+		 * consume free segments.
+		 */
+write_alias:
+		if (super->s_no_object_aliases < MAX_OBJ_ALIASES)
+			return;
+		if (list_empty(&super->s_object_alias)) {
+			/* All aliases are still in btree */
+			return;
+		}
+		log_gc("Write back one alias\n");
+		block = list_entry(super->s_object_alias.next,
+				struct logfs_block, alias_list);
+		block->ops->write_block(block);
+		/*
+		 * To round off the nasty goto logic, we reset round here.  It
+		 * is a safety-net for GC not making any progress and limited
+		 * to something reasonably small.  If incremented it for every
+		 * single alias, the loop could terminate rather quickly.
+		 */
+		round = 0;
+	}
+	LOGFS_BUG(sb);
+}
+
+static int wl_ratelimit(struct super_block *sb, u64 *next_event)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	if (*next_event < super->s_gec) {
+		*next_event = super->s_gec + WL_RATELIMIT;
+		return 0;
+	}
+	return 1;
+}
+
+static void logfs_wl_pass(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct gc_candidate *wl_cand, *free_cand;
+
+	if (wl_ratelimit(sb, &super->s_wl_gec_ostore))
+		return;
+
+	wl_cand = first_in_list(&super->s_ec_list);
+	if (!wl_cand)
+		return;
+	free_cand = first_in_list(&super->s_free_list);
+	if (!free_cand)
+		return;
+
+	if (wl_cand->erase_count < free_cand->erase_count + WL_DELTA) {
+		remove_from_list(wl_cand);
+		__logfs_gc_once(sb, wl_cand);
+	}
+}
+
+/*
+ * The journal needs wear leveling as well.  But moving the journal is an
+ * expensive operation so we try to avoid it as much as possible.  And if we
+ * have to do it, we move the whole journal, not individual segments.
+ *
+ * Ratelimiting is not strictly necessary here, it mainly serves to avoid the
+ * calculations.  First we check whether moving the journal would be a
+ * significant improvement.  That means that a) the current journal segments
+ * have more wear than the future journal segments and b) the current journal
+ * segments have more wear than normal ostore segments.
+ * Rationale for b) is that we don't have to move the journal if it is aging
+ * less than the ostore, even if the reserve segments age even less (they are
+ * excluded from wear leveling, after all).
+ * Next we check that the superblocks have less wear than the journal.  Since
+ * moving the journal requires writing the superblocks, we have to protect the
+ * superblocks even more than the journal.
+ *
+ * Also we double the acceptable wear difference, compared to ostore wear
+ * leveling.  Journal data is read and rewritten rapidly, comparatively.  So
+ * soft errors have much less time to accumulate and we allow the journal to
+ * be a bit worse than the ostore.
+ */
+static void logfs_journal_wl_pass(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct gc_candidate *cand;
+	u32 min_journal_ec = -1, max_reserve_ec = 0;
+	int i;
+
+	if (wl_ratelimit(sb, &super->s_wl_gec_journal))
+		return;
+
+	if (super->s_reserve_list.count < super->s_no_journal_segs) {
+		/* Reserve is not full enough to move complete journal */
+		return;
+	}
+
+	journal_for_each(i)
+		if (super->s_journal_seg[i])
+			min_journal_ec = min(min_journal_ec,
+					super->s_journal_ec[i]);
+	cand = rb_entry(rb_first(&super->s_free_list.rb_tree),
+			struct gc_candidate, rb_node);
+	max_reserve_ec = cand->erase_count;
+	for (i = 0; i < 2; i++) {
+		struct logfs_segment_entry se;
+		u32 segno = seg_no(sb, super->s_sb_ofs[i]);
+		u32 ec;
+
+		logfs_get_segment_entry(sb, segno, &se);
+		ec = be32_to_cpu(se.ec_level) >> 4;
+		max_reserve_ec = max(max_reserve_ec, ec);
+	}
+
+	if (min_journal_ec > max_reserve_ec + 2 * WL_DELTA) {
+		do_logfs_journal_wl_pass(sb);
+	}
+}
+
+void logfs_gc_pass(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	//BUG_ON(mutex_trylock(&logfs_super(sb)->s_w_mutex));
+	/* Write journal before free space is getting saturated with dirty
+	 * objects.
+	 */
+	if (super->s_dirty_used_bytes + super->s_dirty_free_bytes
+			+ LOGFS_MAX_OBJECTSIZE >= super->s_free_bytes)
+		logfs_write_anchor(super->s_master_inode);
+	__logfs_gc_pass(sb, logfs_super(sb)->s_total_levels);
+	logfs_wl_pass(sb);
+	logfs_journal_wl_pass(sb);
+}
+
+static int check_area(struct super_block *sb, int i)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_area[i];
+	struct logfs_object_header oh;
+	u32 segno = area->a_segno;
+	u32 ofs = area->a_used_bytes;
+	__be32 crc;
+	int err;
+
+	if (!area->a_is_open)
+		return 0;
+
+	for (ofs = area->a_used_bytes;
+	     ofs <= super->s_segsize - sizeof(oh);
+	     ofs += (u32)be16_to_cpu(oh.len) + sizeof(oh)) {
+		err = wbuf_read(sb, dev_ofs(sb, segno, ofs), sizeof(oh), &oh);
+		if (err)
+			return err;
+
+		if (!memchr_inv(&oh, 0xff, sizeof(oh)))
+			break;
+
+		crc = logfs_crc32(&oh, sizeof(oh) - 4, 4);
+		if (crc != oh.crc) {
+			printk(KERN_INFO "interrupted header at %llx\n",
+					dev_ofs(sb, segno, ofs));
+			return 0;
+		}
+	}
+	if (ofs != area->a_used_bytes) {
+		printk(KERN_INFO "%x bytes unaccounted data found at %llx\n",
+				ofs - area->a_used_bytes,
+				dev_ofs(sb, segno, area->a_used_bytes));
+		area->a_used_bytes = ofs;
+	}
+	return 0;
+}
+
+int logfs_check_areas(struct super_block *sb)
+{
+	int i, err;
+
+	for_each_area(i) {
+		err = check_area(sb, i);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+static void logfs_init_candlist(struct candidate_list *list, int maxcount,
+		int sort_by_ec)
+{
+	list->count = 0;
+	list->maxcount = maxcount;
+	list->sort_by_ec = sort_by_ec;
+	list->rb_tree = RB_ROOT;
+}
+
+int logfs_init_gc(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	btree_init_mempool32(&super->s_cand_tree, super->s_btree_pool);
+	logfs_init_candlist(&super->s_free_list, LIST_SIZE + SCAN_RATIO, 1);
+	logfs_init_candlist(&super->s_reserve_list,
+			super->s_bad_seg_reserve, 1);
+	for_each_area(i)
+		logfs_init_candlist(&super->s_low_list[i], LIST_SIZE, 0);
+	logfs_init_candlist(&super->s_ec_list, LIST_SIZE, 1);
+	return 0;
+}
+
+static void logfs_cleanup_list(struct super_block *sb,
+		struct candidate_list *list)
+{
+	struct gc_candidate *cand;
+
+	while (list->count) {
+		cand = rb_entry(list->rb_tree.rb_node, struct gc_candidate,
+				rb_node);
+		remove_from_list(cand);
+		free_candidate(sb, cand);
+	}
+	BUG_ON(list->rb_tree.rb_node);
+}
+
+void logfs_cleanup_gc(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	if (!super->s_free_list.count)
+		return;
+
+	/*
+	 * FIXME: The btree may still contain a single empty node.  So we
+	 * call the grim visitor to clean up that mess.  Btree code should
+	 * do it for us, really.
+	 */
+	btree_grim_visitor32(&super->s_cand_tree, 0, NULL);
+	logfs_cleanup_list(sb, &super->s_free_list);
+	logfs_cleanup_list(sb, &super->s_reserve_list);
+	for_each_area(i)
+		logfs_cleanup_list(sb, &super->s_low_list[i]);
+	logfs_cleanup_list(sb, &super->s_ec_list);
+}

fs/logfs/inode.c

···
+/*
+ * fs/logfs/inode.c	- inode handling code
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+#include <linux/writeback.h>
+#include <linux/backing-dev.h>
+
+/*
+ * How soon to reuse old inode numbers?  LogFS doesn't store deleted inodes
+ * on the medium.  It therefore also lacks a method to store the previous
+ * generation number for deleted inodes.  Instead a single generation number
+ * is stored which will be used for new inodes.  Being just a 32bit counter,
+ * this can obvious wrap relatively quickly.  So we only reuse inodes if we
+ * know that a fair number of inodes can be created before we have to increment
+ * the generation again - effectively adding some bits to the counter.
+ * But being too aggressive here means we keep a very large and very sparse
+ * inode file, wasting space on indirect blocks.
+ * So what is a good value?  Beats me.  64k seems moderately bad on both
+ * fronts, so let's use that for now...
+ *
+ * NFS sucks, as everyone already knows.
+ */
+#define INOS_PER_WRAP (0x10000)
+
+/*
+ * Logfs' requirement to read inodes for garbage collection makes life a bit
+ * harder.  GC may have to read inodes that are in I_FREEING state, when they
+ * are being written out - and waiting for GC to make progress, naturally.
+ *
+ * So we cannot just call iget() or some variant of it, but first have to check
+ * wether the inode in question might be in I_FREEING state.  Therefore we
+ * maintain our own per-sb list of "almost deleted" inodes and check against
+ * that list first.  Normally this should be at most 1-2 entries long.
+ *
+ * Also, inodes have logfs-specific reference counting on top of what the vfs
+ * does.  When .destroy_inode is called, normally the reference count will drop
+ * to zero and the inode gets deleted.  But if GC accessed the inode, its
+ * refcount will remain nonzero and final deletion will have to wait.
+ *
+ * As a result we have two sets of functions to get/put inodes:
+ * logfs_safe_iget/logfs_safe_iput	- safe to call from GC context
+ * logfs_iget/iput			- normal version
+ */
+static struct kmem_cache *logfs_inode_cache;
+
+static DEFINE_SPINLOCK(logfs_inode_lock);
+
+static void logfs_inode_setops(struct inode *inode)
+{
+	switch (inode->i_mode & S_IFMT) {
+	case S_IFDIR:
+		inode->i_op = &logfs_dir_iops;
+		inode->i_fop = &logfs_dir_fops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFREG:
+		inode->i_op = &logfs_reg_iops;
+		inode->i_fop = &logfs_reg_fops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFLNK:
+		inode->i_op = &logfs_symlink_iops;
+		inode->i_mapping->a_ops = &logfs_reg_aops;
+		break;
+	case S_IFSOCK:	/* fall through */
+	case S_IFBLK:	/* fall through */
+	case S_IFCHR:	/* fall through */
+	case S_IFIFO:
+		init_special_inode(inode, inode->i_mode, inode->i_rdev);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static struct inode *__logfs_iget(struct super_block *sb, ino_t ino)
+{
+	struct inode *inode = iget_locked(sb, ino);
+	int err;
+
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+	if (!(inode->i_state & I_NEW))
+		return inode;
+
+	err = logfs_read_inode(inode);
+	if (err || inode->i_nlink == 0) {
+		/* inode->i_nlink == 0 can be true when called from
+		 * block validator */
+		/* set i_nlink to 0 to prevent caching */
+		inode->i_nlink = 0;
+		logfs_inode(inode)->li_flags |= LOGFS_IF_ZOMBIE;
+		iget_failed(inode);
+		if (!err)
+			err = -ENOENT;
+		return ERR_PTR(err);
+	}
+
+	logfs_inode_setops(inode);
+	unlock_new_inode(inode);
+	return inode;
+}
+
+struct inode *logfs_iget(struct super_block *sb, ino_t ino)
+{
+	BUG_ON(ino == LOGFS_INO_MASTER);
+	BUG_ON(ino == LOGFS_INO_SEGFILE);
+	return __logfs_iget(sb, ino);
+}
+
+/*
+ * is_cached is set to 1 if we hand out a cached inode, 0 otherwise.
+ * this allows logfs_iput to do the right thing later
+ */
+struct inode *logfs_safe_iget(struct super_block *sb, ino_t ino, int *is_cached)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_inode *li;
+
+	if (ino == LOGFS_INO_MASTER)
+		return super->s_master_inode;
+	if (ino == LOGFS_INO_SEGFILE)
+		return super->s_segfile_inode;
+
+	spin_lock(&logfs_inode_lock);
+	list_for_each_entry(li, &super->s_freeing_list, li_freeing_list)
+		if (li->vfs_inode.i_ino == ino) {
+			li->li_refcount++;
+			spin_unlock(&logfs_inode_lock);
+			*is_cached = 1;
+			return &li->vfs_inode;
+		}
+	spin_unlock(&logfs_inode_lock);
+
+	*is_cached = 0;
+	return __logfs_iget(sb, ino);
+}
+
+static void __logfs_destroy_inode(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	BUG_ON(li->li_block);
+	list_del(&li->li_freeing_list);
+	kmem_cache_free(logfs_inode_cache, li);
+}
+
+static void logfs_destroy_inode(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	BUG_ON(list_empty(&li->li_freeing_list));
+	spin_lock(&logfs_inode_lock);
+	li->li_refcount--;
+	if (li->li_refcount == 0)
+		__logfs_destroy_inode(inode);
+	spin_unlock(&logfs_inode_lock);
+}
+
+void logfs_safe_iput(struct inode *inode, int is_cached)
+{
+	if (inode->i_ino == LOGFS_INO_MASTER)
+		return;
+	if (inode->i_ino == LOGFS_INO_SEGFILE)
+		return;
+
+	if (is_cached) {
+		logfs_destroy_inode(inode);
+		return;
+	}
+
+	iput(inode);
+}
+
+static void logfs_init_inode(struct super_block *sb, struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	li->li_flags	= 0;
+	li->li_height	= 0;
+	li->li_used_bytes = 0;
+	li->li_block	= NULL;
+	inode->i_uid	= 0;
+	inode->i_gid	= 0;
+	inode->i_size	= 0;
+	inode->i_blocks	= 0;
+	inode->i_ctime	= CURRENT_TIME;
+	inode->i_mtime	= CURRENT_TIME;
+	inode->i_nlink	= 1;
+	INIT_LIST_HEAD(&li->li_freeing_list);
+
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		li->li_data[i] = 0;
+
+	return;
+}
+
+static struct inode *logfs_alloc_inode(struct super_block *sb)
+{
+	struct logfs_inode *li;
+
+	li = kmem_cache_alloc(logfs_inode_cache, GFP_NOFS);
+	if (!li)
+		return NULL;
+	logfs_init_inode(sb, &li->vfs_inode);
+	return &li->vfs_inode;
+}
+
+/*
+ * In logfs inodes are written to an inode file.  The inode file, like any
+ * other file, is managed with a inode.  The inode file's inode, aka master
+ * inode, requires special handling in several respects.  First, it cannot be
+ * written to the inode file, so it is stored in the journal instead.
+ *
+ * Secondly, this inode cannot be written back and destroyed before all other
+ * inodes have been written.  The ordering is important.  Linux' VFS is happily
+ * unaware of the ordering constraint and would ordinarily destroy the master
+ * inode at umount time while other inodes are still in use and dirty.  Not
+ * good.
+ *
+ * So logfs makes sure the master inode is not written until all other inodes
+ * have been destroyed.  Sadly, this method has another side-effect.  The VFS
+ * will notice one remaining inode and print a frightening warning message.
+ * Worse, it is impossible to judge whether such a warning was caused by the
+ * master inode or any other inodes have leaked as well.
+ *
+ * Our attempt of solving this is with logfs_new_meta_inode() below.  Its
+ * purpose is to create a new inode that will not trigger the warning if such
+ * an inode is still in use.  An ugly hack, no doubt.  Suggections for
+ * improvement are welcome.
+ */
+struct inode *logfs_new_meta_inode(struct super_block *sb, u64 ino)
+{
+	struct inode *inode;
+
+	inode = logfs_alloc_inode(sb);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	inode->i_mode = S_IFREG;
+	inode->i_ino = ino;
+	inode->i_sb = sb;
+
+	/* This is a blatant copy of alloc_inode code.  We'd need alloc_inode
+	 * to be nonstatic, alas. */
+	{
+		struct address_space * const mapping = &inode->i_data;
+
+		mapping->a_ops = &logfs_reg_aops;
+		mapping->host = inode;
+		mapping->flags = 0;
+		mapping_set_gfp_mask(mapping, GFP_NOFS);
+		mapping->assoc_mapping = NULL;
+		mapping->backing_dev_info = &default_backing_dev_info;
+		inode->i_mapping = mapping;
+		inode->i_nlink = 1;
+	}
+
+	return inode;
+}
+
+struct inode *logfs_read_meta_inode(struct super_block *sb, u64 ino)
+{
+	struct inode *inode;
+	int err;
+
+	inode = logfs_new_meta_inode(sb, ino);
+	if (IS_ERR(inode))
+		return inode;
+
+	err = logfs_read_inode(inode);
+	if (err) {
+		destroy_meta_inode(inode);
+		return ERR_PTR(err);
+	}
+	logfs_inode_setops(inode);
+	return inode;
+}
+
+static int logfs_write_inode(struct inode *inode, int do_sync)
+{
+	int ret;
+	long flags = WF_LOCK;
+
+	/* Can only happen if creat() failed.  Safe to skip. */
+	if (logfs_inode(inode)->li_flags & LOGFS_IF_STILLBORN)
+		return 0;
+
+	ret = __logfs_write_inode(inode, flags);
+	LOGFS_BUG_ON(ret, inode->i_sb);
+	return ret;
+}
+
+void destroy_meta_inode(struct inode *inode)
+{
+	if (inode) {
+		if (inode->i_data.nrpages)
+			truncate_inode_pages(&inode->i_data, 0);
+		logfs_clear_inode(inode);
+		kmem_cache_free(logfs_inode_cache, logfs_inode(inode));
+	}
+}
+
+/* called with inode_lock held */
+static void logfs_drop_inode(struct inode *inode)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	struct logfs_inode *li = logfs_inode(inode);
+
+	spin_lock(&logfs_inode_lock);
+	list_move(&li->li_freeing_list, &super->s_freeing_list);
+	spin_unlock(&logfs_inode_lock);
+	generic_drop_inode(inode);
+}
+
+static void logfs_set_ino_generation(struct super_block *sb,
+		struct inode *inode)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u64 ino;
+
+	mutex_lock(&super->s_journal_mutex);
+	ino = logfs_seek_hole(super->s_master_inode, super->s_last_ino);
+	super->s_last_ino = ino;
+	super->s_inos_till_wrap--;
+	if (super->s_inos_till_wrap < 0) {
+		super->s_last_ino = LOGFS_RESERVED_INOS;
+		super->s_generation++;
+		super->s_inos_till_wrap = INOS_PER_WRAP;
+	}
+	inode->i_ino = ino;
+	inode->i_generation = super->s_generation;
+	mutex_unlock(&super->s_journal_mutex);
+}
+
+struct inode *logfs_new_inode(struct inode *dir, int mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct inode *inode;
+
+	inode = new_inode(sb);
+	if (!inode)
+		return ERR_PTR(-ENOMEM);
+
+	logfs_init_inode(sb, inode);
+
+	/* inherit parent flags */
+	logfs_inode(inode)->li_flags |=
+		logfs_inode(dir)->li_flags & LOGFS_FL_INHERITED;
+
+	inode->i_mode = mode;
+	logfs_set_ino_generation(sb, inode);
+
+	inode->i_uid = current_fsuid();
+	inode->i_gid = current_fsgid();
+	if (dir->i_mode & S_ISGID) {
+		inode->i_gid = dir->i_gid;
+		if (S_ISDIR(mode))
+			inode->i_mode |= S_ISGID;
+	}
+
+	logfs_inode_setops(inode);
+	insert_inode_hash(inode);
+
+	return inode;
+}
+
+static void logfs_init_once(void *_li)
+{
+	struct logfs_inode *li = _li;
+	int i;
+
+	li->li_flags = 0;
+	li->li_used_bytes = 0;
+	li->li_refcount = 1;
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		li->li_data[i] = 0;
+	inode_init_once(&li->vfs_inode);
+}
+
+static int logfs_sync_fs(struct super_block *sb, int wait)
+{
+	/* FIXME: write anchor */
+	logfs_super(sb)->s_devops->sync(sb);
+	return 0;
+}
+
+const struct super_operations logfs_super_operations = {
+	.alloc_inode	= logfs_alloc_inode,
+	.clear_inode	= logfs_clear_inode,
+	.delete_inode	= logfs_delete_inode,
+	.destroy_inode	= logfs_destroy_inode,
+	.drop_inode	= logfs_drop_inode,
+	.write_inode	= logfs_write_inode,
+	.statfs		= logfs_statfs,
+	.sync_fs	= logfs_sync_fs,
+};
+
+int logfs_init_inode_cache(void)
+{
+	logfs_inode_cache = kmem_cache_create("logfs_inode_cache",
+			sizeof(struct logfs_inode), 0, SLAB_RECLAIM_ACCOUNT,
+			logfs_init_once);
+	if (!logfs_inode_cache)
+		return -ENOMEM;
+	return 0;
+}
+
+void logfs_destroy_inode_cache(void)
+{
+	kmem_cache_destroy(logfs_inode_cache);
+}

fs/logfs/journal.c

···
+/*
+ * fs/logfs/journal.c	- journal handling code
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ */
+#include "logfs.h"
+
+static void logfs_calc_free(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u64 reserve, no_segs = super->s_no_segs;
+	s64 free;
+	int i;
+
+	/* superblock segments */
+	no_segs -= 2;
+	super->s_no_journal_segs = 0;
+	/* journal */
+	journal_for_each(i)
+		if (super->s_journal_seg[i]) {
+			no_segs--;
+			super->s_no_journal_segs++;
+		}
+
+	/* open segments plus one extra per level for GC */
+	no_segs -= 2 * super->s_total_levels;
+
+	free = no_segs * (super->s_segsize - LOGFS_SEGMENT_RESERVE);
+	free -= super->s_used_bytes;
+	/* just a bit extra */
+	free -= super->s_total_levels * 4096;
+
+	/* Bad blocks are 'paid' for with speed reserve - the filesystem
+	 * simply gets slower as bad blocks accumulate.  Until the bad blocks
+	 * exceed the speed reserve - then the filesystem gets smaller.
+	 */
+	reserve = super->s_bad_segments + super->s_bad_seg_reserve;
+	reserve *= super->s_segsize - LOGFS_SEGMENT_RESERVE;
+	reserve = max(reserve, super->s_speed_reserve);
+	free -= reserve;
+	if (free < 0)
+		free = 0;
+
+	super->s_free_bytes = free;
+}
+
+static void reserve_sb_and_journal(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct btree_head32 *head = &super->s_reserved_segments;
+	int i, err;
+
+	err = btree_insert32(head, seg_no(sb, super->s_sb_ofs[0]), (void *)1,
+			GFP_KERNEL);
+	BUG_ON(err);
+
+	err = btree_insert32(head, seg_no(sb, super->s_sb_ofs[1]), (void *)1,
+			GFP_KERNEL);
+	BUG_ON(err);
+
+	journal_for_each(i) {
+		if (!super->s_journal_seg[i])
+			continue;
+		err = btree_insert32(head, super->s_journal_seg[i], (void *)1,
+				GFP_KERNEL);
+		BUG_ON(err);
+	}
+}
+
+static void read_dynsb(struct super_block *sb,
+		struct logfs_je_dynsb *dynsb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	super->s_gec		= be64_to_cpu(dynsb->ds_gec);
+	super->s_sweeper	= be64_to_cpu(dynsb->ds_sweeper);
+	super->s_victim_ino	= be64_to_cpu(dynsb->ds_victim_ino);
+	super->s_rename_dir	= be64_to_cpu(dynsb->ds_rename_dir);
+	super->s_rename_pos	= be64_to_cpu(dynsb->ds_rename_pos);
+	super->s_used_bytes	= be64_to_cpu(dynsb->ds_used_bytes);
+	super->s_generation	= be32_to_cpu(dynsb->ds_generation);
+}
+
+static void read_anchor(struct super_block *sb,
+		struct logfs_je_anchor *da)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode = super->s_master_inode;
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	super->s_last_ino = be64_to_cpu(da->da_last_ino);
+	li->li_flags	= 0;
+	li->li_height	= da->da_height;
+	i_size_write(inode, be64_to_cpu(da->da_size));
+	li->li_used_bytes = be64_to_cpu(da->da_used_bytes);
+
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		li->li_data[i] = be64_to_cpu(da->da_data[i]);
+}
+
+static void read_erasecount(struct super_block *sb,
+		struct logfs_je_journal_ec *ec)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	journal_for_each(i)
+		super->s_journal_ec[i] = be32_to_cpu(ec->ec[i]);
+}
+
+static int read_area(struct super_block *sb, struct logfs_je_area *a)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_area[a->gc_level];
+	u64 ofs;
+	u32 writemask = ~(super->s_writesize - 1);
+
+	if (a->gc_level >= LOGFS_NO_AREAS)
+		return -EIO;
+	if (a->vim != VIM_DEFAULT)
+		return -EIO; /* TODO: close area and continue */
+
+	area->a_used_bytes = be32_to_cpu(a->used_bytes);
+	area->a_written_bytes = area->a_used_bytes & writemask;
+	area->a_segno = be32_to_cpu(a->segno);
+	if (area->a_segno)
+		area->a_is_open = 1;
+
+	ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
+	if (super->s_writesize > 1)
+		logfs_buf_recover(area, ofs, a + 1, super->s_writesize);
+	else
+		logfs_buf_recover(area, ofs, NULL, 0);
+	return 0;
+}
+
+static void *unpack(void *from, void *to)
+{
+	struct logfs_journal_header *jh = from;
+	void *data = from + sizeof(struct logfs_journal_header);
+	int err;
+	size_t inlen, outlen;
+
+	inlen = be16_to_cpu(jh->h_len);
+	outlen = be16_to_cpu(jh->h_datalen);
+
+	if (jh->h_compr == COMPR_NONE)
+		memcpy(to, data, inlen);
+	else {
+		err = logfs_uncompress(data, to, inlen, outlen);
+		BUG_ON(err);
+	}
+	return to;
+}
+
+static int __read_je_header(struct super_block *sb, u64 ofs,
+		struct logfs_journal_header *jh)
+{
+	struct logfs_super *super = logfs_super(sb);
+	size_t bufsize = max_t(size_t, sb->s_blocksize, super->s_writesize)
+		+ MAX_JOURNAL_HEADER;
+	u16 type, len, datalen;
+	int err;
+
+	/* read header only */
+	err = wbuf_read(sb, ofs, sizeof(*jh), jh);
+	if (err)
+		return err;
+	type = be16_to_cpu(jh->h_type);
+	len = be16_to_cpu(jh->h_len);
+	datalen = be16_to_cpu(jh->h_datalen);
+	if (len > sb->s_blocksize)
+		return -EIO;
+	if ((type < JE_FIRST) || (type > JE_LAST))
+		return -EIO;
+	if (datalen > bufsize)
+		return -EIO;
+	return 0;
+}
+
+static int __read_je_payload(struct super_block *sb, u64 ofs,
+		struct logfs_journal_header *jh)
+{
+	u16 len;
+	int err;
+
+	len = be16_to_cpu(jh->h_len);
+	err = wbuf_read(sb, ofs + sizeof(*jh), len, jh + 1);
+	if (err)
+		return err;
+	if (jh->h_crc != logfs_crc32(jh, len + sizeof(*jh), 4)) {
+		/* Old code was confused.  It forgot about the header length
+		 * and stopped calculating the crc 16 bytes before the end
+		 * of data - ick!
+		 * FIXME: Remove this hack once the old code is fixed.
+		 */
+		if (jh->h_crc == logfs_crc32(jh, len, 4))
+			WARN_ON_ONCE(1);
+		else
+			return -EIO;
+	}
+	return 0;
+}
+
+/*
+ * jh needs to be large enough to hold the complete entry, not just the header
+ */
+static int __read_je(struct super_block *sb, u64 ofs,
+		struct logfs_journal_header *jh)
+{
+	int err;
+
+	err = __read_je_header(sb, ofs, jh);
+	if (err)
+		return err;
+	return __read_je_payload(sb, ofs, jh);
+}
+
+static int read_je(struct super_block *sb, u64 ofs)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_journal_header *jh = super->s_compressed_je;
+	void *scratch = super->s_je;
+	u16 type, datalen;
+	int err;
+
+	err = __read_je(sb, ofs, jh);
+	if (err)
+		return err;
+	type = be16_to_cpu(jh->h_type);
+	datalen = be16_to_cpu(jh->h_datalen);
+
+	switch (type) {
+	case JE_DYNSB:
+		read_dynsb(sb, unpack(jh, scratch));
+		break;
+	case JE_ANCHOR:
+		read_anchor(sb, unpack(jh, scratch));
+		break;
+	case JE_ERASECOUNT:
+		read_erasecount(sb, unpack(jh, scratch));
+		break;
+	case JE_AREA:
+		read_area(sb, unpack(jh, scratch));
+		break;
+	case JE_OBJ_ALIAS:
+		err = logfs_load_object_aliases(sb, unpack(jh, scratch),
+				datalen);
+		break;
+	default:
+		WARN_ON_ONCE(1);
+		return -EIO;
+	}
+	return err;
+}
+
+static int logfs_read_segment(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_journal_header *jh = super->s_compressed_je;
+	u64 ofs, seg_ofs = dev_ofs(sb, segno, 0);
+	u32 h_ofs, last_ofs = 0;
+	u16 len, datalen, last_len;
+	int i, err;
+
+	/* search for most recent commit */
+	for (h_ofs = 0; h_ofs < super->s_segsize; h_ofs += sizeof(*jh)) {
+		ofs = seg_ofs + h_ofs;
+		err = __read_je_header(sb, ofs, jh);
+		if (err)
+			continue;
+		if (jh->h_type != cpu_to_be16(JE_COMMIT))
+			continue;
+		err = __read_je_payload(sb, ofs, jh);
+		if (err)
+			continue;
+		len = be16_to_cpu(jh->h_len);
+		datalen = be16_to_cpu(jh->h_datalen);
+		if ((datalen > sizeof(super->s_je_array)) ||
+				(datalen % sizeof(__be64)))
+			continue;
+		last_ofs = h_ofs;
+		last_len = datalen;
+		h_ofs += ALIGN(len, sizeof(*jh)) - sizeof(*jh);
+	}
+	/* read commit */
+	if (last_ofs == 0)
+		return -ENOENT;
+	ofs = seg_ofs + last_ofs;
+	log_journal("Read commit from %llx\n", ofs);
+	err = __read_je(sb, ofs, jh);
+	BUG_ON(err); /* We should have caught it in the scan loop already */
+	if (err)
+		return err;
+	/* uncompress */
+	unpack(jh, super->s_je_array);
+	super->s_no_je = last_len / sizeof(__be64);
+	/* iterate over array */
+	for (i = 0; i < super->s_no_je; i++) {
+		err = read_je(sb, be64_to_cpu(super->s_je_array[i]));
+		if (err)
+			return err;
+	}
+	super->s_journal_area->a_segno = segno;
+	return 0;
+}
+
+static u64 read_gec(struct super_block *sb, u32 segno)
+{
+	struct logfs_segment_header sh;
+	__be32 crc;
+	int err;
+
+	if (!segno)
+		return 0;
+	err = wbuf_read(sb, dev_ofs(sb, segno, 0), sizeof(sh), &sh);
+	if (err)
+		return 0;
+	crc = logfs_crc32(&sh, sizeof(sh), 4);
+	if (crc != sh.crc) {
+		WARN_ON(sh.gec != cpu_to_be64(0xffffffffffffffffull));
+		/* Most likely it was just erased */
+		return 0;
+	}
+	return be64_to_cpu(sh.gec);
+}
+
+static int logfs_read_journal(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u64 gec[LOGFS_JOURNAL_SEGS], max;
+	u32 segno;
+	int i, max_i;
+
+	max = 0;
+	max_i = -1;
+	journal_for_each(i) {
+		segno = super->s_journal_seg[i];
+		gec[i] = read_gec(sb, super->s_journal_seg[i]);
+		if (gec[i] > max) {
+			max = gec[i];
+			max_i = i;
+		}
+	}
+	if (max_i == -1)
+		return -EIO;
+	/* FIXME: Try older segments in case of error */
+	return logfs_read_segment(sb, super->s_journal_seg[max_i]);
+}
+
+/*
+ * First search the current segment (outer loop), then pick the next segment
+ * in the array, skipping any zero entries (inner loop).
+ */
+static void journal_get_free_segment(struct logfs_area *area)
+{
+	struct logfs_super *super = logfs_super(area->a_sb);
+	int i;
+
+	journal_for_each(i) {
+		if (area->a_segno != super->s_journal_seg[i])
+			continue;
+
+		do {
+			i++;
+			if (i == LOGFS_JOURNAL_SEGS)
+				i = 0;
+		} while (!super->s_journal_seg[i]);
+
+		area->a_segno = super->s_journal_seg[i];
+		area->a_erase_count = ++(super->s_journal_ec[i]);
+		log_journal("Journal now at %x (ec %x)\n", area->a_segno,
+				area->a_erase_count);
+		return;
+	}
+	BUG();
+}
+
+static void journal_get_erase_count(struct logfs_area *area)
+{
+	/* erase count is stored globally and incremented in
+	 * journal_get_free_segment() - nothing to do here */
+}
+
+static int journal_erase_segment(struct logfs_area *area)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_segment_header sh;
+	u64 ofs;
+	int err;
+
+	err = logfs_erase_segment(sb, area->a_segno);
+	if (err)
+		return err;
+
+	sh.pad = 0;
+	sh.type = SEG_JOURNAL;
+	sh.level = 0;
+	sh.segno = cpu_to_be32(area->a_segno);
+	sh.ec = cpu_to_be32(area->a_erase_count);
+	sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
+	sh.crc = logfs_crc32(&sh, sizeof(sh), 4);
+
+	/* This causes a bug in segment.c.  Not yet. */
+	//logfs_set_segment_erased(sb, area->a_segno, area->a_erase_count, 0);
+
+	ofs = dev_ofs(sb, area->a_segno, 0);
+	area->a_used_bytes = ALIGN(sizeof(sh), 16);
+	logfs_buf_write(area, ofs, &sh, sizeof(sh));
+	return 0;
+}
+
+static size_t __logfs_write_header(struct logfs_super *super,
+		struct logfs_journal_header *jh, size_t len, size_t datalen,
+		u16 type, u8 compr)
+{
+	jh->h_len	= cpu_to_be16(len);
+	jh->h_type	= cpu_to_be16(type);
+	jh->h_version	= cpu_to_be16(++super->s_last_version);
+	jh->h_datalen	= cpu_to_be16(datalen);
+	jh->h_compr	= compr;
+	jh->h_pad[0]	= 'H';
+	jh->h_pad[1]	= 'A';
+	jh->h_pad[2]	= 'T';
+	jh->h_crc	= logfs_crc32(jh, len + sizeof(*jh), 4);
+	return ALIGN(len, 16) + sizeof(*jh);
+}
+
+static size_t logfs_write_header(struct logfs_super *super,
+		struct logfs_journal_header *jh, size_t datalen, u16 type)
+{
+	size_t len = datalen;
+
+	return __logfs_write_header(super, jh, len, datalen, type, COMPR_NONE);
+}
+
+static inline size_t logfs_journal_erasecount_size(struct logfs_super *super)
+{
+	return LOGFS_JOURNAL_SEGS * sizeof(__be32);
+}
+
+static void *logfs_write_erasecount(struct super_block *sb, void *_ec,
+		u16 *type, size_t *len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_je_journal_ec *ec = _ec;
+	int i;
+
+	journal_for_each(i)
+		ec->ec[i] = cpu_to_be32(super->s_journal_ec[i]);
+	*type = JE_ERASECOUNT;
+	*len = logfs_journal_erasecount_size(super);
+	return ec;
+}
+
+static void account_shadow(void *_shadow, unsigned long _sb, u64 ignore,
+		size_t ignore2)
+{
+	struct logfs_shadow *shadow = _shadow;
+	struct super_block *sb = (void *)_sb;
+	struct logfs_super *super = logfs_super(sb);
+
+	/* consume new space */
+	super->s_free_bytes	  -= shadow->new_len;
+	super->s_used_bytes	  += shadow->new_len;
+	super->s_dirty_used_bytes -= shadow->new_len;
+
+	/* free up old space */
+	super->s_free_bytes	  += shadow->old_len;
+	super->s_used_bytes	  -= shadow->old_len;
+	super->s_dirty_free_bytes -= shadow->old_len;
+
+	logfs_set_segment_used(sb, shadow->old_ofs, -shadow->old_len);
+	logfs_set_segment_used(sb, shadow->new_ofs, shadow->new_len);
+
+	log_journal("account_shadow(%llx, %llx, %x) %llx->%llx %x->%x\n",
+			shadow->ino, shadow->bix, shadow->gc_level,
+			shadow->old_ofs, shadow->new_ofs,
+			shadow->old_len, shadow->new_len);
+	mempool_free(shadow, super->s_shadow_pool);
+}
+
+static void account_shadows(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode = super->s_master_inode;
+	struct logfs_inode *li = logfs_inode(inode);
+	struct shadow_tree *tree = &super->s_shadow_tree;
+
+	btree_grim_visitor64(&tree->new, (unsigned long)sb, account_shadow);
+	btree_grim_visitor64(&tree->old, (unsigned long)sb, account_shadow);
+
+	if (li->li_block) {
+		/*
+		 * We never actually use the structure, when attached to the
+		 * master inode.  But it is easier to always free it here than
+		 * to have checks in several places elsewhere when allocating
+		 * it.
+		 */
+		li->li_block->ops->free_block(sb, li->li_block);
+	}
+	BUG_ON((s64)li->li_used_bytes < 0);
+}
+
+static void *__logfs_write_anchor(struct super_block *sb, void *_da,
+		u16 *type, size_t *len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_je_anchor *da = _da;
+	struct inode *inode = super->s_master_inode;
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	da->da_height	= li->li_height;
+	da->da_last_ino = cpu_to_be64(super->s_last_ino);
+	da->da_size	= cpu_to_be64(i_size_read(inode));
+	da->da_used_bytes = cpu_to_be64(li->li_used_bytes);
+	for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+		da->da_data[i] = cpu_to_be64(li->li_data[i]);
+	*type = JE_ANCHOR;
+	*len = sizeof(*da);
+	return da;
+}
+
+static void *logfs_write_dynsb(struct super_block *sb, void *_dynsb,
+		u16 *type, size_t *len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_je_dynsb *dynsb = _dynsb;
+
+	dynsb->ds_gec		= cpu_to_be64(super->s_gec);
+	dynsb->ds_sweeper	= cpu_to_be64(super->s_sweeper);
+	dynsb->ds_victim_ino	= cpu_to_be64(super->s_victim_ino);
+	dynsb->ds_rename_dir	= cpu_to_be64(super->s_rename_dir);
+	dynsb->ds_rename_pos	= cpu_to_be64(super->s_rename_pos);
+	dynsb->ds_used_bytes	= cpu_to_be64(super->s_used_bytes);
+	dynsb->ds_generation	= cpu_to_be32(super->s_generation);
+	*type = JE_DYNSB;
+	*len = sizeof(*dynsb);
+	return dynsb;
+}
+
+static void write_wbuf(struct super_block *sb, struct logfs_area *area,
+		void *wbuf)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	u64 ofs;
+	pgoff_t index;
+	int page_ofs;
+	struct page *page;
+
+	ofs = dev_ofs(sb, area->a_segno,
+			area->a_used_bytes & ~(super->s_writesize - 1));
+	index = ofs >> PAGE_SHIFT;
+	page_ofs = ofs & (PAGE_SIZE - 1);
+
+	page = find_lock_page(mapping, index);
+	BUG_ON(!page);
+	memcpy(wbuf, page_address(page) + page_ofs, super->s_writesize);
+	unlock_page(page);
+}
+
+static void *logfs_write_area(struct super_block *sb, void *_a,
+		u16 *type, size_t *len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_area[super->s_sum_index];
+	struct logfs_je_area *a = _a;
+
+	a->vim = VIM_DEFAULT;
+	a->gc_level = super->s_sum_index;
+	a->used_bytes = cpu_to_be32(area->a_used_bytes);
+	a->segno = cpu_to_be32(area->a_segno);
+	if (super->s_writesize > 1)
+		write_wbuf(sb, area, a + 1);
+
+	*type = JE_AREA;
+	*len = sizeof(*a) + super->s_writesize;
+	return a;
+}
+
+static void *logfs_write_commit(struct super_block *sb, void *h,
+		u16 *type, size_t *len)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	*type = JE_COMMIT;
+	*len = super->s_no_je * sizeof(__be64);
+	return super->s_je_array;
+}
+
+static size_t __logfs_write_je(struct super_block *sb, void *buf, u16 type,
+		size_t len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	void *header = super->s_compressed_je;
+	void *data = header + sizeof(struct logfs_journal_header);
+	ssize_t compr_len, pad_len;
+	u8 compr = COMPR_ZLIB;
+
+	if (len == 0)
+		return logfs_write_header(super, header, 0, type);
+
+	compr_len = logfs_compress(buf, data, len, sb->s_blocksize);
+	if (compr_len < 0 || type == JE_ANCHOR) {
+		BUG_ON(len > sb->s_blocksize);
+		memcpy(data, buf, len);
+		compr_len = len;
+		compr = COMPR_NONE;
+	}
+
+	pad_len = ALIGN(compr_len, 16);
+	memset(data + compr_len, 0, pad_len - compr_len);
+
+	return __logfs_write_header(super, header, compr_len, len, type, compr);
+}
+
+static s64 logfs_get_free_bytes(struct logfs_area *area, size_t *bytes,
+		int must_pad)
+{
+	u32 writesize = logfs_super(area->a_sb)->s_writesize;
+	s32 ofs;
+	int ret;
+
+	ret = logfs_open_area(area, *bytes);
+	if (ret)
+		return -EAGAIN;
+
+	ofs = area->a_used_bytes;
+	area->a_used_bytes += *bytes;
+
+	if (must_pad) {
+		area->a_used_bytes = ALIGN(area->a_used_bytes, writesize);
+		*bytes = area->a_used_bytes - ofs;
+	}
+
+	return dev_ofs(area->a_sb, area->a_segno, ofs);
+}
+
+static int logfs_write_je_buf(struct super_block *sb, void *buf, u16 type,
+		size_t buf_len)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_journal_area;
+	struct logfs_journal_header *jh = super->s_compressed_je;
+	size_t len;
+	int must_pad = 0;
+	s64 ofs;
+
+	len = __logfs_write_je(sb, buf, type, buf_len);
+	if (jh->h_type == cpu_to_be16(JE_COMMIT))
+		must_pad = 1;
+
+	ofs = logfs_get_free_bytes(area, &len, must_pad);
+	if (ofs < 0)
+		return ofs;
+	logfs_buf_write(area, ofs, super->s_compressed_je, len);
+	super->s_je_array[super->s_no_je++] = cpu_to_be64(ofs);
+	return 0;
+}
+
+static int logfs_write_je(struct super_block *sb,
+		void* (*write)(struct super_block *sb, void *scratch,
+			u16 *type, size_t *len))
+{
+	void *buf;
+	size_t len;
+	u16 type;
+
+	buf = write(sb, logfs_super(sb)->s_je, &type, &len);
+	return logfs_write_je_buf(sb, buf, type, len);
+}
+
+int write_alias_journal(struct super_block *sb, u64 ino, u64 bix,
+		level_t level, int child_no, __be64 val)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_obj_alias *oa = super->s_je;
+	int err = 0, fill = super->s_je_fill;
+
+	log_aliases("logfs_write_obj_aliases #%x(%llx, %llx, %x, %x) %llx\n",
+			fill, ino, bix, level, child_no, be64_to_cpu(val));
+	oa[fill].ino = cpu_to_be64(ino);
+	oa[fill].bix = cpu_to_be64(bix);
+	oa[fill].val = val;
+	oa[fill].level = (__force u8)level;
+	oa[fill].child_no = cpu_to_be16(child_no);
+	fill++;
+	if (fill >= sb->s_blocksize / sizeof(*oa)) {
+		err = logfs_write_je_buf(sb, oa, JE_OBJ_ALIAS, sb->s_blocksize);
+		fill = 0;
+	}
+
+	super->s_je_fill = fill;
+	return err;
+}
+
+static int logfs_write_obj_aliases(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int err;
+
+	log_journal("logfs_write_obj_aliases: %d aliases to write\n",
+			super->s_no_object_aliases);
+	super->s_je_fill = 0;
+	err = logfs_write_obj_aliases_pagecache(sb);
+	if (err)
+		return err;
+
+	if (super->s_je_fill)
+		err = logfs_write_je_buf(sb, super->s_je, JE_OBJ_ALIAS,
+				super->s_je_fill
+				* sizeof(struct logfs_obj_alias));
+	return err;
+}
+
+/*
+ * Write all journal entries.  The goto logic ensures that all journal entries
+ * are written whenever a new segment is used.  It is ugly and potentially a
+ * bit wasteful, but robustness is more important.  With this we can *always*
+ * erase all journal segments except the one containing the most recent commit.
+ */
+void logfs_write_anchor(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_journal_area;
+	int i, err;
+
+	BUG_ON(logfs_super(sb)->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
+	mutex_lock(&super->s_journal_mutex);
+
+	/* Do this first or suffer corruption */
+	logfs_sync_segments(sb);
+	account_shadows(sb);
+
+again:
+	super->s_no_je = 0;
+	for_each_area(i) {
+		if (!super->s_area[i]->a_is_open)
+			continue;
+		super->s_sum_index = i;
+		err = logfs_write_je(sb, logfs_write_area);
+		if (err)
+			goto again;
+	}
+	err = logfs_write_obj_aliases(sb);
+	if (err)
+		goto again;
+	err = logfs_write_je(sb, logfs_write_erasecount);
+	if (err)
+		goto again;
+	err = logfs_write_je(sb, __logfs_write_anchor);
+	if (err)
+		goto again;
+	err = logfs_write_je(sb, logfs_write_dynsb);
+	if (err)
+		goto again;
+	/*
+	 * Order is imperative.  First we sync all writes, including the
+	 * non-committed journal writes.  Then we write the final commit and
+	 * sync the current journal segment.
+	 * There is a theoretical bug here.  Syncing the journal segment will
+	 * write a number of journal entries and the final commit.  All these
+	 * are written in a single operation.  If the device layer writes the
+	 * data back-to-front, the commit will precede the other journal
+	 * entries, leaving a race window.
+	 * Two fixes are possible.  Preferred is to fix the device layer to
+	 * ensure writes happen front-to-back.  Alternatively we can insert
+	 * another logfs_sync_area() super->s_devops->sync() combo before
+	 * writing the commit.
+	 */
+	/*
+	 * On another subject, super->s_devops->sync is usually not necessary.
+	 * Unless called from sys_sync or friends, a barrier would suffice.
+	 */
+	super->s_devops->sync(sb);
+	err = logfs_write_je(sb, logfs_write_commit);
+	if (err)
+		goto again;
+	log_journal("Write commit to %llx\n",
+			be64_to_cpu(super->s_je_array[super->s_no_je - 1]));
+	logfs_sync_area(area);
+	BUG_ON(area->a_used_bytes != area->a_written_bytes);
+	super->s_devops->sync(sb);
+
+	mutex_unlock(&super->s_journal_mutex);
+	return;
+}
+
+void do_logfs_journal_wl_pass(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_area *area = super->s_journal_area;
+	u32 segno, ec;
+	int i, err;
+
+	log_journal("Journal requires wear-leveling.\n");
+	/* Drop old segments */
+	journal_for_each(i)
+		if (super->s_journal_seg[i]) {
+			logfs_set_segment_unreserved(sb,
+					super->s_journal_seg[i],
+					super->s_journal_ec[i]);
+			super->s_journal_seg[i] = 0;
+			super->s_journal_ec[i] = 0;
+		}
+	/* Get new segments */
+	for (i = 0; i < super->s_no_journal_segs; i++) {
+		segno = get_best_cand(sb, &super->s_reserve_list, &ec);
+		super->s_journal_seg[i] = segno;
+		super->s_journal_ec[i] = ec;
+		logfs_set_segment_reserved(sb, segno);
+	}
+	/* Manually move journal_area */
+	area->a_segno = super->s_journal_seg[0];
+	area->a_is_open = 0;
+	area->a_used_bytes = 0;
+	/* Write journal */
+	logfs_write_anchor(super->s_master_inode);
+	/* Write superblocks */
+	err = logfs_write_sb(sb);
+	BUG_ON(err);
+}
+
+static const struct logfs_area_ops journal_area_ops = {
+	.get_free_segment	= journal_get_free_segment,
+	.get_erase_count	= journal_get_erase_count,
+	.erase_segment		= journal_erase_segment,
+};
+
+int logfs_init_journal(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	size_t bufsize = max_t(size_t, sb->s_blocksize, super->s_writesize)
+		+ MAX_JOURNAL_HEADER;
+	int ret = -ENOMEM;
+
+	mutex_init(&super->s_journal_mutex);
+	btree_init_mempool32(&super->s_reserved_segments, super->s_btree_pool);
+
+	super->s_je = kzalloc(bufsize, GFP_KERNEL);
+	if (!super->s_je)
+		return ret;
+
+	super->s_compressed_je = kzalloc(bufsize, GFP_KERNEL);
+	if (!super->s_compressed_je)
+		return ret;
+
+	super->s_master_inode = logfs_new_meta_inode(sb, LOGFS_INO_MASTER);
+	if (IS_ERR(super->s_master_inode))
+		return PTR_ERR(super->s_master_inode);
+
+	ret = logfs_read_journal(sb);
+	if (ret)
+		return -EIO;
+
+	reserve_sb_and_journal(sb);
+	logfs_calc_free(sb);
+
+	super->s_journal_area->a_ops = &journal_area_ops;
+	return 0;
+}
+
+void logfs_cleanup_journal(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	btree_grim_visitor32(&super->s_reserved_segments, 0, NULL);
+	destroy_meta_inode(super->s_master_inode);
+	super->s_master_inode = NULL;
+
+	kfree(super->s_compressed_je);
+	kfree(super->s_je);
+}

fs/logfs/logfs.h

···
+/*
+ * fs/logfs/logfs.h
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ *
+ * Private header for logfs.
+ */
+#ifndef FS_LOGFS_LOGFS_H
+#define FS_LOGFS_LOGFS_H
+
+#undef __CHECK_ENDIAN__
+#define __CHECK_ENDIAN__
+
+#include <linux/btree.h>
+#include <linux/crc32.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/mempool.h>
+#include <linux/pagemap.h>
+#include <linux/mtd/mtd.h>
+#include "logfs_abi.h"
+
+#define LOGFS_DEBUG_SUPER	(0x0001)
+#define LOGFS_DEBUG_SEGMENT	(0x0002)
+#define LOGFS_DEBUG_JOURNAL	(0x0004)
+#define LOGFS_DEBUG_DIR		(0x0008)
+#define LOGFS_DEBUG_FILE	(0x0010)
+#define LOGFS_DEBUG_INODE	(0x0020)
+#define LOGFS_DEBUG_READWRITE	(0x0040)
+#define LOGFS_DEBUG_GC		(0x0080)
+#define LOGFS_DEBUG_GC_NOISY	(0x0100)
+#define LOGFS_DEBUG_ALIASES	(0x0200)
+#define LOGFS_DEBUG_BLOCKMOVE	(0x0400)
+#define LOGFS_DEBUG_ALL		(0xffffffff)
+
+#define LOGFS_DEBUG		(0x01)
+/*
+ * To enable specific log messages, simply define LOGFS_DEBUG to match any
+ * or all of the above.
+ */
+#ifndef LOGFS_DEBUG
+#define LOGFS_DEBUG		(0)
+#endif
+
+#define log_cond(cond, fmt, arg...) do {	\
+	if (cond)				\
+		printk(KERN_DEBUG fmt, ##arg);	\
+} while (0)
+
+#define log_super(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_SUPER, fmt, ##arg)
+#define log_segment(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_SEGMENT, fmt, ##arg)
+#define log_journal(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_JOURNAL, fmt, ##arg)
+#define log_dir(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_DIR, fmt, ##arg)
+#define log_file(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_FILE, fmt, ##arg)
+#define log_inode(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_INODE, fmt, ##arg)
+#define log_readwrite(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_READWRITE, fmt, ##arg)
+#define log_gc(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_GC, fmt, ##arg)
+#define log_gc_noisy(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_GC_NOISY, fmt, ##arg)
+#define log_aliases(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_ALIASES, fmt, ##arg)
+#define log_blockmove(fmt, arg...) \
+	log_cond(LOGFS_DEBUG & LOGFS_DEBUG_BLOCKMOVE, fmt, ##arg)
+
+#define PG_pre_locked		PG_owner_priv_1
+#define PagePreLocked(page)	test_bit(PG_pre_locked, &(page)->flags)
+#define SetPagePreLocked(page)	set_bit(PG_pre_locked, &(page)->flags)
+#define ClearPagePreLocked(page) clear_bit(PG_pre_locked, &(page)->flags)
+
+/* FIXME: This should really be somewhere in the 64bit area. */
+#define LOGFS_LINK_MAX		(1<<30)
+
+/* Read-only filesystem */
+#define LOGFS_SB_FLAG_RO	0x0001
+#define LOGFS_SB_FLAG_SEG_ALIAS	0x0002
+#define LOGFS_SB_FLAG_OBJ_ALIAS	0x0004
+#define LOGFS_SB_FLAG_SHUTDOWN	0x0008
+
+/* Write Control Flags */
+#define WF_LOCK			0x01 /* take write lock */
+#define WF_WRITE		0x02 /* write block */
+#define WF_DELETE		0x04 /* delete old block */
+
+typedef u8 __bitwise level_t;
+typedef u8 __bitwise gc_level_t;
+
+#define LEVEL(level) ((__force level_t)(level))
+#define GC_LEVEL(gc_level) ((__force gc_level_t)(gc_level))
+
+#define SUBLEVEL(level) ( (void)((level) == LEVEL(1)),	\
+		(__force level_t)((__force u8)(level) - 1) )
+
+/**
+ * struct logfs_area - area management information
+ *
+ * @a_sb:			the superblock this area belongs to
+ * @a_is_open:			1 if the area is currently open, else 0
+ * @a_segno:			segment number of area
+ * @a_written_bytes:		number of bytes already written back
+ * @a_used_bytes:		number of used bytes
+ * @a_ops:			area operations (either journal or ostore)
+ * @a_erase_count:		erase count
+ * @a_level:			GC level
+ */
+struct logfs_area { /* a segment open for writing */
+	struct super_block *a_sb;
+	int	a_is_open;
+	u32	a_segno;
+	u32	a_written_bytes;
+	u32	a_used_bytes;
+	const struct logfs_area_ops *a_ops;
+	u32	a_erase_count;
+	gc_level_t a_level;
+};
+
+/**
+ * struct logfs_area_ops - area operations
+ *
+ * @get_free_segment:		fill area->ofs with the offset of a free segment
+ * @get_erase_count:		fill area->erase_count (needs area->ofs)
+ * @erase_segment:		erase and setup segment
+ */
+struct logfs_area_ops {
+	void	(*get_free_segment)(struct logfs_area *area);
+	void	(*get_erase_count)(struct logfs_area *area);
+	int	(*erase_segment)(struct logfs_area *area);
+};
+
+/**
+ * struct logfs_device_ops - device access operations
+ *
+ * @readpage:			read one page (mm page)
+ * @writeseg:			write one segment.  may be a partial segment
+ * @erase:			erase one segment
+ * @read:			read from the device
+ * @erase:			erase part of the device
+ */
+struct logfs_device_ops {
+	struct page *(*find_first_sb)(struct super_block *sb, u64 *ofs);
+	struct page *(*find_last_sb)(struct super_block *sb, u64 *ofs);
+	int (*write_sb)(struct super_block *sb, struct page *page);
+	int (*readpage)(void *_sb, struct page *page);
+	void (*writeseg)(struct super_block *sb, u64 ofs, size_t len);
+	int (*erase)(struct super_block *sb, loff_t ofs, size_t len);
+	void (*sync)(struct super_block *sb);
+	void (*put_device)(struct super_block *sb);
+};
+
+/**
+ * struct candidate_list - list of similar candidates
+ */
+struct candidate_list {
+	struct rb_root rb_tree;
+	int count;
+	int maxcount;
+	int sort_by_ec;
+};
+
+/**
+ * struct gc_candidate - "candidate" segment to be garbage collected next
+ *
+ * @list:			list (either free of low)
+ * @segno:			segment number
+ * @valid:			number of valid bytes
+ * @erase_count:		erase count of segment
+ * @dist:			distance from tree root
+ *
+ * Candidates can be on two lists.  The free list contains electees rather
+ * than candidates - segments that no longer contain any valid data.  The
+ * low list contains candidates to be picked for GC.  It should be kept
+ * short.  It is not required to always pick a perfect candidate.  In the
+ * worst case GC will have to move more data than absolutely necessary.
+ */
+struct gc_candidate {
+	struct rb_node rb_node;
+	struct candidate_list *list;
+	u32	segno;
+	u32	valid;
+	u32	erase_count;
+	u8	dist;
+};
+
+/**
+ * struct logfs_journal_entry - temporary structure used during journal scan
+ *
+ * @used:
+ * @version:			normalized version
+ * @len:			length
+ * @offset:			offset
+ */
+struct logfs_journal_entry {
+	int used;
+	s16 version;
+	u16 len;
+	u16 datalen;
+	u64 offset;
+};
+
+enum transaction_state {
+	CREATE_1 = 1,
+	CREATE_2,
+	UNLINK_1,
+	UNLINK_2,
+	CROSS_RENAME_1,
+	CROSS_RENAME_2,
+	TARGET_RENAME_1,
+	TARGET_RENAME_2,
+	TARGET_RENAME_3
+};
+
+/**
+ * struct logfs_transaction - essential fields to support atomic dirops
+ *
+ * @ino:			target inode
+ * @dir:			inode of directory containing dentry
+ * @pos:			pos of dentry in directory
+ */
+struct logfs_transaction {
+	enum transaction_state state;
+	u64	 ino;
+	u64	 dir;
+	u64	 pos;
+};
+
+/**
+ * struct logfs_shadow - old block in the shadow of a not-yet-committed new one
+ * @old_ofs:			offset of old block on medium
+ * @new_ofs:			offset of new block on medium
+ * @ino:			inode number
+ * @bix:			block index
+ * @old_len:			size of old block, including header
+ * @new_len:			size of new block, including header
+ * @level:			block level
+ */
+struct logfs_shadow {
+	u64 old_ofs;
+	u64 new_ofs;
+	u64 ino;
+	u64 bix;
+	int old_len;
+	int new_len;
+	gc_level_t gc_level;
+};
+
+/**
+ * struct shadow_tree
+ * @new:			shadows where old_ofs==0, indexed by new_ofs
+ * @old:			shadows where old_ofs!=0, indexed by old_ofs
+ */
+struct shadow_tree {
+	struct btree_head64 new;
+	struct btree_head64 old;
+};
+
+struct object_alias_item {
+	struct list_head list;
+	__be64 val;
+	int child_no;
+};
+
+/**
+ * struct logfs_block - contains any block state
+ * @type:			indirect block or inode
+ * @full:			number of fully populated children
+ * @partial:			number of partially populated children
+ *
+ * Most blocks are directly represented by page cache pages.  But when a block
+ * becomes dirty, is part of a transaction, contains aliases or is otherwise
+ * special, a struct logfs_block is allocated to track the additional state.
+ * Inodes are very similar to indirect blocks, so they can also get one of
+ * these structures added when appropriate.
+ */
+#define BLOCK_INDIRECT	1	/* Indirect block */
+#define BLOCK_INODE	2	/* Inode */
+struct logfs_block_ops;
+struct logfs_block {
+	struct list_head alias_list;
+	struct list_head item_list;
+	struct super_block *sb;
+	u64 ino;
+	u64 bix;
+	level_t level;
+	struct page *page;
+	struct inode *inode;
+	struct logfs_transaction *ta;
+	unsigned long alias_map[LOGFS_BLOCK_FACTOR / BITS_PER_LONG];
+	struct logfs_block_ops *ops;
+	int full;
+	int partial;
+	int reserved_bytes;
+};
+
+typedef int write_alias_t(struct super_block *sb, u64 ino, u64 bix,
+		level_t level, int child_no, __be64 val);
+struct logfs_block_ops {
+	void	(*write_block)(struct logfs_block *block);
+	gc_level_t	(*block_level)(struct logfs_block *block);
+	void	(*free_block)(struct super_block *sb, struct logfs_block*block);
+	int	(*write_alias)(struct super_block *sb,
+			struct logfs_block *block,
+			write_alias_t *write_one_alias);
+};
+
+struct logfs_super {
+	struct mtd_info *s_mtd;			/* underlying device */
+	struct block_device *s_bdev;		/* underlying device */
+	const struct logfs_device_ops *s_devops;/* device access */
+	struct inode	*s_master_inode;	/* inode file */
+	struct inode	*s_segfile_inode;	/* segment file */
+	struct inode *s_mapping_inode;		/* device mapping */
+	atomic_t s_pending_writes;		/* outstanting bios */
+	long	 s_flags;
+	mempool_t *s_btree_pool;		/* for btree nodes */
+	mempool_t *s_alias_pool;		/* aliases in segment.c */
+	u64	 s_feature_incompat;
+	u64	 s_feature_ro_compat;
+	u64	 s_feature_compat;
+	u64	 s_feature_flags;
+	u64	 s_sb_ofs[2];
+	/* alias.c fields */
+	struct btree_head32 s_segment_alias;	/* remapped segments */
+	int	 s_no_object_aliases;
+	struct list_head s_object_alias;	/* remapped objects */
+	struct btree_head128 s_object_alias_tree; /* remapped objects */
+	struct mutex s_object_alias_mutex;
+	/* dir.c fields */
+	struct mutex s_dirop_mutex;		/* for creat/unlink/rename */
+	u64	 s_victim_ino;			/* used for atomic dir-ops */
+	u64	 s_rename_dir;			/* source directory ino */
+	u64	 s_rename_pos;			/* position of source dd */
+	/* gc.c fields */
+	long	 s_segsize;			/* size of a segment */
+	int	 s_segshift;			/* log2 of segment size */
+	long	 s_segmask;			/* 1 << s_segshift - 1 */
+	long	 s_no_segs;			/* segments on device */
+	long	 s_no_journal_segs;		/* segments used for journal */
+	long	 s_no_blocks;			/* blocks per segment */
+	long	 s_writesize;			/* minimum write size */
+	int	 s_writeshift;			/* log2 of write size */
+	u64	 s_size;			/* filesystem size */
+	struct logfs_area *s_area[LOGFS_NO_AREAS];	/* open segment array */
+	u64	 s_gec;				/* global erase count */
+	u64	 s_wl_gec_ostore;		/* time of last wl event */
+	u64	 s_wl_gec_journal;		/* time of last wl event */
+	u64	 s_sweeper;			/* current sweeper pos */
+	u8	 s_ifile_levels;		/* max level of ifile */
+	u8	 s_iblock_levels;		/* max level of regular files */
+	u8	 s_data_levels;			/* # of segments to leaf block*/
+	u8	 s_total_levels;		/* sum of above three */
+	struct btree_head32 s_cand_tree;	/* all candidates */
+	struct candidate_list s_free_list;	/* 100% free segments */
+	struct candidate_list s_reserve_list;	/* Bad segment reserve */
+	struct candidate_list s_low_list[LOGFS_NO_AREAS];/* good candidates */
+	struct candidate_list s_ec_list;	/* wear level candidates */
+	struct btree_head32 s_reserved_segments;/* sb, journal, bad, etc. */
+	/* inode.c fields */
+	u64	 s_last_ino;			/* highest ino used */
+	long	 s_inos_till_wrap;
+	u32	 s_generation;			/* i_generation for new files */
+	struct list_head s_freeing_list;	/* inodes being freed */
+	/* journal.c fields */
+	struct mutex s_journal_mutex;
+	void	*s_je;				/* journal entry to compress */
+	void	*s_compressed_je;		/* block to write to journal */
+	u32	 s_journal_seg[LOGFS_JOURNAL_SEGS]; /* journal segments */
+	u32	 s_journal_ec[LOGFS_JOURNAL_SEGS]; /* journal erasecounts */
+	u64	 s_last_version;
+	struct logfs_area *s_journal_area;	/* open journal segment */
+	__be64	s_je_array[64];
+	int	s_no_je;
+
+	int	 s_sum_index;			/* for the 12 summaries */
+	struct shadow_tree s_shadow_tree;
+	int	 s_je_fill;			/* index of current je */
+	/* readwrite.c fields */
+	struct mutex s_write_mutex;
+	int	 s_lock_count;
+	mempool_t *s_block_pool;		/* struct logfs_block pool */
+	mempool_t *s_shadow_pool;		/* struct logfs_shadow pool */
+	/*
+	 * Space accounting:
+	 * - s_used_bytes specifies space used to store valid data objects.
+	 * - s_dirty_used_bytes is space used to store non-committed data
+	 *   objects.  Those objects have already been written themselves,
+	 *   but they don't become valid until all indirect blocks up to the
+	 *   journal have been written as well.
+	 * - s_dirty_free_bytes is space used to store the old copy of a
+	 *   replaced object, as long as the replacement is non-committed.
+	 *   In other words, it is the amount of space freed when all dirty
+	 *   blocks are written back.
+	 * - s_free_bytes is the amount of free space available for any
+	 *   purpose.
+	 * - s_root_reserve is the amount of free space available only to
+	 *   the root user.  Non-privileged users can no longer write once
+	 *   this watermark has been reached.
+	 * - s_speed_reserve is space which remains unused to speed up
+	 *   garbage collection performance.
+	 * - s_dirty_pages is the space reserved for currently dirty pages.
+	 *   It is a pessimistic estimate, so some/most will get freed on
+	 *   page writeback.
+	 *
+	 * s_used_bytes + s_free_bytes + s_speed_reserve = total usable size
+	 */
+	u64	 s_free_bytes;
+	u64	 s_used_bytes;
+	u64	 s_dirty_free_bytes;
+	u64	 s_dirty_used_bytes;
+	u64	 s_root_reserve;
+	u64	 s_speed_reserve;
+	u64	 s_dirty_pages;
+	/* Bad block handling:
+	 * - s_bad_seg_reserve is a number of segments usually kept
+	 *   free.  When encountering bad blocks, the affected segment's data
+	 *   is _temporarily_ moved to a reserved segment.
+	 * - s_bad_segments is the number of known bad segments.
+	 */
+	u32	 s_bad_seg_reserve;
+	u32	 s_bad_segments;
+};
+
+/**
+ * struct logfs_inode - in-memory inode
+ *
+ * @vfs_inode:			struct inode
+ * @li_data:			data pointers
+ * @li_used_bytes:		number of used bytes
+ * @li_freeing_list:		used to track inodes currently being freed
+ * @li_flags:			inode flags
+ * @li_refcount:		number of internal (GC-induced) references
+ */
+struct logfs_inode {
+	struct inode vfs_inode;
+	u64	li_data[LOGFS_EMBEDDED_FIELDS];
+	u64	li_used_bytes;
+	struct list_head li_freeing_list;
+	struct logfs_block *li_block;
+	u32	li_flags;
+	u8	li_height;
+	int	li_refcount;
+};
+
+#define journal_for_each(__i) for (__i = 0; __i < LOGFS_JOURNAL_SEGS; __i++)
+#define for_each_area(__i) for (__i = 0; __i < LOGFS_NO_AREAS; __i++)
+#define for_each_area_down(__i) for (__i = LOGFS_NO_AREAS - 1; __i >= 0; __i--)
+
+/* compr.c */
+int logfs_compress(void *in, void *out, size_t inlen, size_t outlen);
+int logfs_uncompress(void *in, void *out, size_t inlen, size_t outlen);
+int __init logfs_compr_init(void);
+void logfs_compr_exit(void);
+
+/* dev_bdev.c */
+#ifdef CONFIG_BLOCK
+int logfs_get_sb_bdev(struct file_system_type *type, int flags,
+		const char *devname, struct vfsmount *mnt);
+#else
+static inline int logfs_get_sb_bdev(struct file_system_type *type, int flags,
+		const char *devname, struct vfsmount *mnt)
+{
+	return -ENODEV;
+}
+#endif
+
+/* dev_mtd.c */
+#ifdef CONFIG_MTD
+int logfs_get_sb_mtd(struct file_system_type *type, int flags,
+		int mtdnr, struct vfsmount *mnt);
+#else
+static inline int logfs_get_sb_mtd(struct file_system_type *type, int flags,
+		int mtdnr, struct vfsmount *mnt)
+{
+	return -ENODEV;
+}
+#endif
+
+/* dir.c */
+extern const struct inode_operations logfs_symlink_iops;
+extern const struct inode_operations logfs_dir_iops;
+extern const struct file_operations logfs_dir_fops;
+int logfs_replay_journal(struct super_block *sb);
+
+/* file.c */
+extern const struct inode_operations logfs_reg_iops;
+extern const struct file_operations logfs_reg_fops;
+extern const struct address_space_operations logfs_reg_aops;
+int logfs_readpage(struct file *file, struct page *page);
+int logfs_ioctl(struct inode *inode, struct file *file, unsigned int cmd,
+		unsigned long arg);
+int logfs_fsync(struct file *file, struct dentry *dentry, int datasync);
+
+/* gc.c */
+u32 get_best_cand(struct super_block *sb, struct candidate_list *list, u32 *ec);
+void logfs_gc_pass(struct super_block *sb);
+int logfs_check_areas(struct super_block *sb);
+int logfs_init_gc(struct super_block *sb);
+void logfs_cleanup_gc(struct super_block *sb);
+
+/* inode.c */
+extern const struct super_operations logfs_super_operations;
+struct inode *logfs_iget(struct super_block *sb, ino_t ino);
+struct inode *logfs_safe_iget(struct super_block *sb, ino_t ino, int *cookie);
+void logfs_safe_iput(struct inode *inode, int cookie);
+struct inode *logfs_new_inode(struct inode *dir, int mode);
+struct inode *logfs_new_meta_inode(struct super_block *sb, u64 ino);
+struct inode *logfs_read_meta_inode(struct super_block *sb, u64 ino);
+int logfs_init_inode_cache(void);
+void logfs_destroy_inode_cache(void);
+void destroy_meta_inode(struct inode *inode);
+void logfs_set_blocks(struct inode *inode, u64 no);
+/* these logically belong into inode.c but actually reside in readwrite.c */
+int logfs_read_inode(struct inode *inode);
+int __logfs_write_inode(struct inode *inode, long flags);
+void logfs_delete_inode(struct inode *inode);
+void logfs_clear_inode(struct inode *inode);
+
+/* journal.c */
+void logfs_write_anchor(struct inode *inode);
+int logfs_init_journal(struct super_block *sb);
+void logfs_cleanup_journal(struct super_block *sb);
+int write_alias_journal(struct super_block *sb, u64 ino, u64 bix,
+		level_t level, int child_no, __be64 val);
+void do_logfs_journal_wl_pass(struct super_block *sb);
+
+/* readwrite.c */
+pgoff_t logfs_pack_index(u64 bix, level_t level);
+void logfs_unpack_index(pgoff_t index, u64 *bix, level_t *level);
+int logfs_inode_write(struct inode *inode, const void *buf, size_t count,
+		loff_t bix, long flags, struct shadow_tree *shadow_tree);
+int logfs_readpage_nolock(struct page *page);
+int logfs_write_buf(struct inode *inode, struct page *page, long flags);
+int logfs_delete(struct inode *inode, pgoff_t index,
+		struct shadow_tree *shadow_tree);
+int logfs_rewrite_block(struct inode *inode, u64 bix, u64 ofs,
+		gc_level_t gc_level, long flags);
+int logfs_is_valid_block(struct super_block *sb, u64 ofs, u64 ino, u64 bix,
+		gc_level_t gc_level);
+int logfs_truncate(struct inode *inode, u64 size);
+u64 logfs_seek_hole(struct inode *inode, u64 bix);
+u64 logfs_seek_data(struct inode *inode, u64 bix);
+int logfs_open_segfile(struct super_block *sb);
+int logfs_init_rw(struct super_block *sb);
+void logfs_cleanup_rw(struct super_block *sb);
+void logfs_add_transaction(struct inode *inode, struct logfs_transaction *ta);
+void logfs_del_transaction(struct inode *inode, struct logfs_transaction *ta);
+void logfs_write_block(struct logfs_block *block, long flags);
+int logfs_write_obj_aliases_pagecache(struct super_block *sb);
+void logfs_get_segment_entry(struct super_block *sb, u32 segno,
+		struct logfs_segment_entry *se);
+void logfs_set_segment_used(struct super_block *sb, u64 ofs, int increment);
+void logfs_set_segment_erased(struct super_block *sb, u32 segno, u32 ec,
+		gc_level_t gc_level);
+void logfs_set_segment_reserved(struct super_block *sb, u32 segno);
+void logfs_set_segment_unreserved(struct super_block *sb, u32 segno, u32 ec);
+struct logfs_block *__alloc_block(struct super_block *sb,
+		u64 ino, u64 bix, level_t level);
+void __free_block(struct super_block *sb, struct logfs_block *block);
+void btree_write_block(struct logfs_block *block);
+void initialize_block_counters(struct page *page, struct logfs_block *block,
+		__be64 *array, int page_is_empty);
+int logfs_exist_block(struct inode *inode, u64 bix);
+int get_page_reserve(struct inode *inode, struct page *page);
+extern struct logfs_block_ops indirect_block_ops;
+
+/* segment.c */
+int logfs_erase_segment(struct super_block *sb, u32 ofs);
+int wbuf_read(struct super_block *sb, u64 ofs, size_t len, void *buf);
+int logfs_segment_read(struct inode *inode, struct page *page, u64 ofs, u64 bix,
+		level_t level);
+int logfs_segment_write(struct inode *inode, struct page *page,
+		struct logfs_shadow *shadow);
+int logfs_segment_delete(struct inode *inode, struct logfs_shadow *shadow);
+int logfs_load_object_aliases(struct super_block *sb,
+		struct logfs_obj_alias *oa, int count);
+void move_page_to_btree(struct page *page);
+int logfs_init_mapping(struct super_block *sb);
+void logfs_sync_area(struct logfs_area *area);
+void logfs_sync_segments(struct super_block *sb);
+
+/* area handling */
+int logfs_init_areas(struct super_block *sb);
+void logfs_cleanup_areas(struct super_block *sb);
+int logfs_open_area(struct logfs_area *area, size_t bytes);
+void __logfs_buf_write(struct logfs_area *area, u64 ofs, void *buf, size_t len,
+		int use_filler);
+
+static inline void logfs_buf_write(struct logfs_area *area, u64 ofs,
+		void *buf, size_t len)
+{
+	__logfs_buf_write(area, ofs, buf, len, 0);
+}
+
+static inline void logfs_buf_recover(struct logfs_area *area, u64 ofs,
+		void *buf, size_t len)
+{
+	__logfs_buf_write(area, ofs, buf, len, 1);
+}
+
+/* super.c */
+struct page *emergency_read_begin(struct address_space *mapping, pgoff_t index);
+void emergency_read_end(struct page *page);
+void logfs_crash_dump(struct super_block *sb);
+void *memchr_inv(const void *s, int c, size_t n);
+int logfs_statfs(struct dentry *dentry, struct kstatfs *stats);
+int logfs_get_sb_device(struct file_system_type *type, int flags,
+		struct mtd_info *mtd, struct block_device *bdev,
+		const struct logfs_device_ops *devops, struct vfsmount *mnt);
+int logfs_check_ds(struct logfs_disk_super *ds);
+int logfs_write_sb(struct super_block *sb);
+
+static inline struct logfs_super *logfs_super(struct super_block *sb)
+{
+	return sb->s_fs_info;
+}
+
+static inline struct logfs_inode *logfs_inode(struct inode *inode)
+{
+	return container_of(inode, struct logfs_inode, vfs_inode);
+}
+
+static inline void logfs_set_ro(struct super_block *sb)
+{
+	logfs_super(sb)->s_flags |= LOGFS_SB_FLAG_RO;
+}
+
+#define LOGFS_BUG(sb) do {					\
+	struct super_block *__sb = sb;				\
+	logfs_crash_dump(__sb);					\
+	logfs_super(__sb)->s_flags |= LOGFS_SB_FLAG_RO;		\
+	BUG();							\
+} while (0)
+
+#define LOGFS_BUG_ON(condition, sb) \
+	do { if (unlikely(condition)) LOGFS_BUG((sb)); } while (0)
+
+static inline __be32 logfs_crc32(void *data, size_t len, size_t skip)
+{
+	return cpu_to_be32(crc32(~0, data+skip, len-skip));
+}
+
+static inline u8 logfs_type(struct inode *inode)
+{
+	return (inode->i_mode >> 12) & 15;
+}
+
+static inline pgoff_t logfs_index(struct super_block *sb, u64 pos)
+{
+	return pos >> sb->s_blocksize_bits;
+}
+
+static inline u64 dev_ofs(struct super_block *sb, u32 segno, u32 ofs)
+{
+	return ((u64)segno << logfs_super(sb)->s_segshift) + ofs;
+}
+
+static inline u32 seg_no(struct super_block *sb, u64 ofs)
+{
+	return ofs >> logfs_super(sb)->s_segshift;
+}
+
+static inline u32 seg_ofs(struct super_block *sb, u64 ofs)
+{
+	return ofs & logfs_super(sb)->s_segmask;
+}
+
+static inline u64 seg_align(struct super_block *sb, u64 ofs)
+{
+	return ofs & ~logfs_super(sb)->s_segmask;
+}
+
+static inline struct logfs_block *logfs_block(struct page *page)
+{
+	return (void *)page->private;
+}
+
+static inline level_t shrink_level(gc_level_t __level)
+{
+	u8 level = (__force u8)__level;
+
+	if (level >= LOGFS_MAX_LEVELS)
+		level -= LOGFS_MAX_LEVELS;
+	return (__force level_t)level;
+}
+
+static inline gc_level_t expand_level(u64 ino, level_t __level)
+{
+	u8 level = (__force u8)__level;
+
+	if (ino == LOGFS_INO_MASTER) {
+		/* ifile has seperate areas */
+		level += LOGFS_MAX_LEVELS;
+	}
+	return (__force gc_level_t)level;
+}
+
+static inline int logfs_block_shift(struct super_block *sb, level_t level)
+{
+	level = shrink_level((__force gc_level_t)level);
+	return (__force int)level * (sb->s_blocksize_bits - 3);
+}
+
+static inline u64 logfs_block_mask(struct super_block *sb, level_t level)
+{
+	return ~0ull << logfs_block_shift(sb, level);
+}
+
+static inline struct logfs_area *get_area(struct super_block *sb,
+		gc_level_t gc_level)
+{
+	return logfs_super(sb)->s_area[(__force u8)gc_level];
+}
+
+#endif

fs/logfs/logfs_abi.h

···
+/*
+ * fs/logfs/logfs_abi.h
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ *
+ * Public header for logfs.
+ */
+#ifndef FS_LOGFS_LOGFS_ABI_H
+#define FS_LOGFS_LOGFS_ABI_H
+
+/* For out-of-kernel compiles */
+#ifndef BUILD_BUG_ON
+#define BUILD_BUG_ON(condition) /**/
+#endif
+
+#define SIZE_CHECK(type, size)					\
+static inline void check_##type(void)				\
+{								\
+	BUILD_BUG_ON(sizeof(struct type) != (size));		\
+}
+
+/*
+ * Throughout the logfs code, we're constantly dealing with blocks at
+ * various positions or offsets.  To remove confusion, we stricly
+ * distinguish between a "position" - the logical position within a
+ * file and an "offset" - the physical location within the device.
+ *
+ * Any usage of the term offset for a logical location or position for
+ * a physical one is a bug and should get fixed.
+ */
+
+/*
+ * Block are allocated in one of several segments depending on their
+ * level.  The following levels are used:
+ *  0	- regular data block
+ *  1	- i1 indirect blocks
+ *  2	- i2 indirect blocks
+ *  3	- i3 indirect blocks
+ *  4	- i4 indirect blocks
+ *  5	- i5 indirect blocks
+ *  6	- ifile data blocks
+ *  7	- ifile i1 indirect blocks
+ *  8	- ifile i2 indirect blocks
+ *  9	- ifile i3 indirect blocks
+ * 10	- ifile i4 indirect blocks
+ * 11	- ifile i5 indirect blocks
+ * Potential levels to be used in the future:
+ * 12	- gc recycled blocks, long-lived data
+ * 13	- replacement blocks, short-lived data
+ *
+ * Levels 1-11 are necessary for robust gc operations and help seperate
+ * short-lived metadata from longer-lived file data.  In the future,
+ * file data should get seperated into several segments based on simple
+ * heuristics.  Old data recycled during gc operation is expected to be
+ * long-lived.  New data is of uncertain life expectancy.  New data
+ * used to replace older blocks in existing files is expected to be
+ * short-lived.
+ */
+
+
+/* Magic numbers.  64bit for superblock, 32bit for statfs f_type */
+#define LOGFS_MAGIC		0xb21f205ac97e8168ull
+#define LOGFS_MAGIC_U32		0xc97e8168u
+
+/*
+ * Various blocksize related macros.  Blocksize is currently fixed at 4KiB.
+ * Sooner or later that should become configurable and the macros replaced
+ * by something superblock-dependent.  Pointers in indirect blocks are and
+ * will remain 64bit.
+ *
+ * LOGFS_BLOCKSIZE	- self-explaining
+ * LOGFS_BLOCK_FACTOR	- number of pointers per indirect block
+ * LOGFS_BLOCK_BITS	- log2 of LOGFS_BLOCK_FACTOR, used for shifts
+ */
+#define LOGFS_BLOCKSIZE		(4096ull)
+#define LOGFS_BLOCK_FACTOR	(LOGFS_BLOCKSIZE / sizeof(u64))
+#define LOGFS_BLOCK_BITS	(9)
+
+/*
+ * Number of blocks at various levels of indirection.  There are 16 direct
+ * block pointers plus a single indirect pointer.
+ */
+#define I0_BLOCKS		(16)
+#define I1_BLOCKS		LOGFS_BLOCK_FACTOR
+#define I2_BLOCKS		(LOGFS_BLOCK_FACTOR * I1_BLOCKS)
+#define I3_BLOCKS		(LOGFS_BLOCK_FACTOR * I2_BLOCKS)
+#define I4_BLOCKS		(LOGFS_BLOCK_FACTOR * I3_BLOCKS)
+#define I5_BLOCKS		(LOGFS_BLOCK_FACTOR * I4_BLOCKS)
+
+#define INDIRECT_INDEX		I0_BLOCKS
+#define LOGFS_EMBEDDED_FIELDS	(I0_BLOCKS + 1)
+
+/*
+ * Sizes at which files require another level of indirection.  Files smaller
+ * than LOGFS_EMBEDDED_SIZE can be completely stored in the inode itself,
+ * similar like ext2 fast symlinks.
+ *
+ * Data at a position smaller than LOGFS_I0_SIZE is accessed through the
+ * direct pointers, else through the 1x indirect pointer and so forth.
+ */
+#define LOGFS_EMBEDDED_SIZE	(LOGFS_EMBEDDED_FIELDS * sizeof(u64))
+#define LOGFS_I0_SIZE		(I0_BLOCKS * LOGFS_BLOCKSIZE)
+#define LOGFS_I1_SIZE		(I1_BLOCKS * LOGFS_BLOCKSIZE)
+#define LOGFS_I2_SIZE		(I2_BLOCKS * LOGFS_BLOCKSIZE)
+#define LOGFS_I3_SIZE		(I3_BLOCKS * LOGFS_BLOCKSIZE)
+#define LOGFS_I4_SIZE		(I4_BLOCKS * LOGFS_BLOCKSIZE)
+#define LOGFS_I5_SIZE		(I5_BLOCKS * LOGFS_BLOCKSIZE)
+
+/*
+ * Each indirect block pointer must have this flag set, if all block pointers
+ * behind it are set, i.e. there is no hole hidden in the shadow of this
+ * indirect block pointer.
+ */
+#define LOGFS_FULLY_POPULATED (1ULL << 63)
+#define pure_ofs(ofs) (ofs & ~LOGFS_FULLY_POPULATED)
+
+/*
+ * LogFS needs to seperate data into levels.  Each level is defined as the
+ * maximal possible distance from the master inode (inode of the inode file).
+ * Data blocks reside on level 0, 1x indirect block on level 1, etc.
+ * Inodes reside on level 6, indirect blocks for the inode file on levels 7-11.
+ * This effort is necessary to guarantee garbage collection to always make
+ * progress.
+ *
+ * LOGFS_MAX_INDIRECT is the maximal indirection through indirect blocks,
+ * LOGFS_MAX_LEVELS is one more for the actual data level of a file.  It is
+ * the maximal number of levels for one file.
+ * LOGFS_NO_AREAS is twice that, as the inode file and regular files are
+ * effectively stacked on top of each other.
+ */
+#define LOGFS_MAX_INDIRECT	(5)
+#define LOGFS_MAX_LEVELS	(LOGFS_MAX_INDIRECT + 1)
+#define LOGFS_NO_AREAS		(2 * LOGFS_MAX_LEVELS)
+
+/* Maximum size of filenames */
+#define LOGFS_MAX_NAMELEN	(255)
+
+/* Number of segments in the primary journal. */
+#define LOGFS_JOURNAL_SEGS	(16)
+
+/* Maximum number of free/erased/etc. segments in journal entries */
+#define MAX_CACHED_SEGS		(64)
+
+
+/*
+ * LOGFS_OBJECT_HEADERSIZE is the size of a single header in the object store,
+ * LOGFS_MAX_OBJECTSIZE the size of the largest possible object, including
+ * its header,
+ * LOGFS_SEGMENT_RESERVE is the amount of space reserved for each segment for
+ * its segment header and the padded space at the end when no further objects
+ * fit.
+ */
+#define LOGFS_OBJECT_HEADERSIZE	(0x1c)
+#define LOGFS_SEGMENT_HEADERSIZE (0x18)
+#define LOGFS_MAX_OBJECTSIZE	(LOGFS_OBJECT_HEADERSIZE + LOGFS_BLOCKSIZE)
+#define LOGFS_SEGMENT_RESERVE	\
+	(LOGFS_SEGMENT_HEADERSIZE + LOGFS_MAX_OBJECTSIZE - 1)
+
+/*
+ * Segment types:
+ * SEG_SUPER	- Data or indirect block
+ * SEG_JOURNAL	- Inode
+ * SEG_OSTORE	- Dentry
+ */
+enum {
+	SEG_SUPER	= 0x01,
+	SEG_JOURNAL	= 0x02,
+	SEG_OSTORE	= 0x03,
+};
+
+/**
+ * struct logfs_segment_header - per-segment header in the ostore
+ *
+ * @crc:			crc32 of header (there is no data)
+ * @pad:			unused, must be 0
+ * @type:			segment type, see above
+ * @level:			GC level for all objects in this segment
+ * @segno:			segment number
+ * @ec:				erase count for this segment
+ * @gec:			global erase count at time of writing
+ */
+struct logfs_segment_header {
+	__be32	crc;
+	__be16	pad;
+	__u8	type;
+	__u8	level;
+	__be32	segno;
+	__be32	ec;
+	__be64	gec;
+};
+
+SIZE_CHECK(logfs_segment_header, LOGFS_SEGMENT_HEADERSIZE);
+
+/**
+ * struct logfs_disk_super - on-medium superblock
+ *
+ * @ds_magic:			magic number, must equal LOGFS_MAGIC
+ * @ds_crc:			crc32 of structure starting with the next field
+ * @ds_ifile_levels:		maximum number of levels for ifile
+ * @ds_iblock_levels:		maximum number of levels for regular files
+ * @ds_data_levels:		number of seperate levels for data
+ * @pad0:			reserved, must be 0
+ * @ds_feature_incompat:	incompatible filesystem features
+ * @ds_feature_ro_compat:	read-only compatible filesystem features
+ * @ds_feature_compat:		compatible filesystem features
+ * @ds_flags:			flags
+ * @ds_segment_shift:		log2 of segment size
+ * @ds_block_shift:		log2 of block size
+ * @ds_write_shift:		log2 of write size
+ * @pad1:			reserved, must be 0
+ * @ds_journal_seg:		segments used by primary journal
+ * @ds_root_reserve:		bytes reserved for the superuser
+ * @ds_speed_reserve:		bytes reserved to speed up GC
+ * @ds_bad_seg_reserve:		number of segments reserved to handle bad blocks
+ * @pad2:			reserved, must be 0
+ * @pad3:			reserved, must be 0
+ *
+ * Contains only read-only fields.  Read-write fields like the amount of used
+ * space is tracked in the dynamic superblock, which is stored in the journal.
+ */
+struct logfs_disk_super {
+	struct logfs_segment_header ds_sh;
+	__be64	ds_magic;
+
+	__be32	ds_crc;
+	__u8	ds_ifile_levels;
+	__u8	ds_iblock_levels;
+	__u8	ds_data_levels;
+	__u8	ds_segment_shift;
+	__u8	ds_block_shift;
+	__u8	ds_write_shift;
+	__u8	pad0[6];
+
+	__be64	ds_filesystem_size;
+	__be32	ds_segment_size;
+	__be32  ds_bad_seg_reserve;
+
+	__be64	ds_feature_incompat;
+	__be64	ds_feature_ro_compat;
+
+	__be64	ds_feature_compat;
+	__be64	ds_feature_flags;
+
+	__be64	ds_root_reserve;
+	__be64  ds_speed_reserve;
+
+	__be32	ds_journal_seg[LOGFS_JOURNAL_SEGS];
+
+	__be64	ds_super_ofs[2];
+	__be64	pad3[8];
+};
+
+SIZE_CHECK(logfs_disk_super, 256);
+
+/*
+ * Object types:
+ * OBJ_BLOCK	- Data or indirect block
+ * OBJ_INODE	- Inode
+ * OBJ_DENTRY	- Dentry
+ */
+enum {
+	OBJ_BLOCK	= 0x04,
+	OBJ_INODE	= 0x05,
+	OBJ_DENTRY	= 0x06,
+};
+
+/**
+ * struct logfs_object_header - per-object header in the ostore
+ *
+ * @crc:			crc32 of header, excluding data_crc
+ * @len:			length of data
+ * @type:			object type, see above
+ * @compr:			compression type
+ * @ino:			inode number
+ * @bix:			block index
+ * @data_crc:			crc32 of payload
+ */
+struct logfs_object_header {
+	__be32	crc;
+	__be16	len;
+	__u8	type;
+	__u8	compr;
+	__be64	ino;
+	__be64	bix;
+	__be32	data_crc;
+} __attribute__((packed));
+
+SIZE_CHECK(logfs_object_header, LOGFS_OBJECT_HEADERSIZE);
+
+/*
+ * Reserved inode numbers:
+ * LOGFS_INO_MASTER	- master inode (for inode file)
+ * LOGFS_INO_ROOT	- root directory
+ * LOGFS_INO_SEGFILE	- per-segment used bytes and erase count
+ */
+enum {
+	LOGFS_INO_MAPPING	= 0x00,
+	LOGFS_INO_MASTER	= 0x01,
+	LOGFS_INO_ROOT		= 0x02,
+	LOGFS_INO_SEGFILE	= 0x03,
+	LOGFS_RESERVED_INOS	= 0x10,
+};
+
+/*
+ * Inode flags.  High bits should never be written to the medium.  They are
+ * reserved for in-memory usage.
+ * Low bits should either remain in sync with the corresponding FS_*_FL or
+ * reuse slots that obviously don't make sense for logfs.
+ *
+ * LOGFS_IF_DIRTY	Inode must be written back
+ * LOGFS_IF_ZOMBIE	Inode has been deleted
+ * LOGFS_IF_STILLBORN	-ENOSPC happened when creating inode
+ */
+#define LOGFS_IF_COMPRESSED	0x00000004 /* == FS_COMPR_FL */
+#define LOGFS_IF_DIRTY		0x20000000
+#define LOGFS_IF_ZOMBIE		0x40000000
+#define LOGFS_IF_STILLBORN	0x80000000
+
+/* Flags available to chattr */
+#define LOGFS_FL_USER_VISIBLE	(LOGFS_IF_COMPRESSED)
+#define LOGFS_FL_USER_MODIFIABLE (LOGFS_IF_COMPRESSED)
+/* Flags inherited from parent directory on file/directory creation */
+#define LOGFS_FL_INHERITED	(LOGFS_IF_COMPRESSED)
+
+/**
+ * struct logfs_disk_inode - on-medium inode
+ *
+ * @di_mode:			file mode
+ * @di_pad:			reserved, must be 0
+ * @di_flags:			inode flags, see above
+ * @di_uid:			user id
+ * @di_gid:			group id
+ * @di_ctime:			change time
+ * @di_mtime:			modify time
+ * @di_refcount:		reference count (aka nlink or link count)
+ * @di_generation:		inode generation, for nfs
+ * @di_used_bytes:		number of bytes used
+ * @di_size:			file size
+ * @di_data:			data pointers
+ */
+struct logfs_disk_inode {
+	__be16	di_mode;
+	__u8	di_height;
+	__u8	di_pad;
+	__be32	di_flags;
+	__be32	di_uid;
+	__be32	di_gid;
+
+	__be64	di_ctime;
+	__be64	di_mtime;
+
+	__be64	di_atime;
+	__be32	di_refcount;
+	__be32	di_generation;
+
+	__be64	di_used_bytes;
+	__be64	di_size;
+
+	__be64	di_data[LOGFS_EMBEDDED_FIELDS];
+};
+
+SIZE_CHECK(logfs_disk_inode, 200);
+
+#define INODE_POINTER_OFS \
+	(offsetof(struct logfs_disk_inode, di_data) / sizeof(__be64))
+#define INODE_USED_OFS \
+	(offsetof(struct logfs_disk_inode, di_used_bytes) / sizeof(__be64))
+#define INODE_SIZE_OFS \
+	(offsetof(struct logfs_disk_inode, di_size) / sizeof(__be64))
+#define INODE_HEIGHT_OFS	(0)
+
+/**
+ * struct logfs_disk_dentry - on-medium dentry structure
+ *
+ * @ino:			inode number
+ * @namelen:			length of file name
+ * @type:			file type, identical to bits 12..15 of mode
+ * @name:			file name
+ */
+/* FIXME: add 6 bytes of padding to remove the __packed */
+struct logfs_disk_dentry {
+	__be64	ino;
+	__be16	namelen;
+	__u8	type;
+	__u8	name[LOGFS_MAX_NAMELEN];
+} __attribute__((packed));
+
+SIZE_CHECK(logfs_disk_dentry, 266);
+
+#define RESERVED		0xffffffff
+#define BADSEG			0xffffffff
+/**
+ * struct logfs_segment_entry - segment file entry
+ *
+ * @ec_level:			erase count and level
+ * @valid:			number of valid bytes
+ *
+ * Segment file contains one entry for every segment.  ec_level contains the
+ * erasecount in the upper 28 bits and the level in the lower 4 bits.  An
+ * ec_level of BADSEG (-1) identifies bad segments.  valid contains the number
+ * of valid bytes or RESERVED (-1 again) if the segment is used for either the
+ * superblock or the journal, or when the segment is bad.
+ */
+struct logfs_segment_entry {
+	__be32	ec_level;
+	__be32	valid;
+};
+
+SIZE_CHECK(logfs_segment_entry, 8);
+
+/**
+ * struct logfs_journal_header - header for journal entries (JEs)
+ *
+ * @h_crc:			crc32 of journal entry
+ * @h_len:			length of compressed journal entry,
+ *				not including header
+ * @h_datalen:			length of uncompressed data
+ * @h_type:			JE type
+ * @h_version:			unnormalized version of journal entry
+ * @h_compr:			compression type
+ * @h_pad:			reserved
+ */
+struct logfs_journal_header {
+	__be32	h_crc;
+	__be16	h_len;
+	__be16	h_datalen;
+	__be16	h_type;
+	__be16	h_version;
+	__u8	h_compr;
+	__u8	h_pad[3];
+};
+
+SIZE_CHECK(logfs_journal_header, 16);
+
+/*
+ * Life expectency of data.
+ * VIM_DEFAULT		- default vim
+ * VIM_SEGFILE		- for segment file only - very short-living
+ * VIM_GC		- GC'd data - likely long-living
+ */
+enum logfs_vim {
+	VIM_DEFAULT	= 0,
+	VIM_SEGFILE	= 1,
+};
+
+/**
+ * struct logfs_je_area - wbuf header
+ *
+ * @segno:			segment number of area
+ * @used_bytes:			number of bytes already used
+ * @gc_level:			GC level
+ * @vim:			life expectancy of data
+ *
+ * "Areas" are segments currently being used for writing.  There is at least
+ * one area per GC level.  Several may be used to seperate long-living from
+ * short-living data.  If an area with unknown vim is encountered, it can
+ * simply be closed.
+ * The write buffer immediately follow this header.
+ */
+struct logfs_je_area {
+	__be32	segno;
+	__be32	used_bytes;
+	__u8	gc_level;
+	__u8	vim;
+} __attribute__((packed));
+
+SIZE_CHECK(logfs_je_area, 10);
+
+#define MAX_JOURNAL_HEADER \
+	(sizeof(struct logfs_journal_header) + sizeof(struct logfs_je_area))
+
+/**
+ * struct logfs_je_dynsb - dynamic superblock
+ *
+ * @ds_gec:			global erase count
+ * @ds_sweeper:			current position of GC "sweeper"
+ * @ds_rename_dir:		source directory ino (see dir.c documentation)
+ * @ds_rename_pos:		position of source dd (see dir.c documentation)
+ * @ds_victim_ino:		victims of incomplete dir operation (see dir.c)
+ * @ds_victim_ino:		parent inode of victim (see dir.c)
+ * @ds_used_bytes:		number of used bytes
+ */
+struct logfs_je_dynsb {
+	__be64	ds_gec;
+	__be64	ds_sweeper;
+
+	__be64	ds_rename_dir;
+	__be64	ds_rename_pos;
+
+	__be64	ds_victim_ino;
+	__be64	ds_victim_parent; /* XXX */
+
+	__be64	ds_used_bytes;
+	__be32	ds_generation;
+	__be32	pad;
+};
+
+SIZE_CHECK(logfs_je_dynsb, 64);
+
+/**
+ * struct logfs_je_anchor - anchor of filesystem tree, aka master inode
+ *
+ * @da_size:			size of inode file
+ * @da_last_ino:		last created inode
+ * @da_used_bytes:		number of bytes used
+ * @da_data:			data pointers
+ */
+struct logfs_je_anchor {
+	__be64	da_size;
+	__be64	da_last_ino;
+
+	__be64	da_used_bytes;
+	u8	da_height;
+	u8	pad[7];
+
+	__be64	da_data[LOGFS_EMBEDDED_FIELDS];
+};
+
+SIZE_CHECK(logfs_je_anchor, 168);
+
+/**
+ * struct logfs_je_spillout - spillout entry (from 1st to 2nd journal)
+ *
+ * @so_segment:			segments used for 2nd journal
+ *
+ * Length of the array is given by h_len field in the header.
+ */
+struct logfs_je_spillout {
+	__be64	so_segment[0];
+};
+
+SIZE_CHECK(logfs_je_spillout, 0);
+
+/**
+ * struct logfs_je_journal_ec - erase counts for all journal segments
+ *
+ * @ec:				erase count
+ *
+ * Length of the array is given by h_len field in the header.
+ */
+struct logfs_je_journal_ec {
+	__be32	ec[0];
+};
+
+SIZE_CHECK(logfs_je_journal_ec, 0);
+
+/**
+ * struct logfs_je_free_segments - list of free segmetns with erase count
+ */
+struct logfs_je_free_segments {
+	__be32	segno;
+	__be32	ec;
+};
+
+SIZE_CHECK(logfs_je_free_segments, 8);
+
+/**
+ * struct logfs_seg_alias - list of segment aliases
+ */
+struct logfs_seg_alias {
+	__be32	old_segno;
+	__be32	new_segno;
+};
+
+SIZE_CHECK(logfs_seg_alias, 8);
+
+/**
+ * struct logfs_obj_alias - list of object aliases
+ */
+struct logfs_obj_alias {
+	__be64	ino;
+	__be64	bix;
+	__be64	val;
+	u8	level;
+	u8	pad[5];
+	__be16	child_no;
+};
+
+SIZE_CHECK(logfs_obj_alias, 32);
+
+/**
+ * Compression types.
+ *
+ * COMPR_NONE	- uncompressed
+ * COMPR_ZLIB	- compressed with zlib
+ */
+enum {
+	COMPR_NONE	= 0,
+	COMPR_ZLIB	= 1,
+};
+
+/*
+ * Journal entries come in groups of 16.  First group contains unique
+ * entries, next groups contain one entry per level
+ *
+ * JE_FIRST	- smallest possible journal entry number
+ *
+ * JEG_BASE	- base group, containing unique entries
+ * JE_COMMIT	- commit entry, validates all previous entries
+ * JE_DYNSB	- dynamic superblock, anything that ought to be in the
+ *		  superblock but cannot because it is read-write data
+ * JE_ANCHOR	- anchor aka master inode aka inode file's inode
+ * JE_ERASECOUNT  erasecounts for all journal segments
+ * JE_SPILLOUT	- unused
+ * JE_SEG_ALIAS	- aliases segments
+ * JE_AREA	- area description
+ *
+ * JE_LAST	- largest possible journal entry number
+ */
+enum {
+	JE_FIRST	= 0x01,
+
+	JEG_BASE	= 0x00,
+	JE_COMMIT	= 0x02,
+	JE_DYNSB	= 0x03,
+	JE_ANCHOR	= 0x04,
+	JE_ERASECOUNT	= 0x05,
+	JE_SPILLOUT	= 0x06,
+	JE_OBJ_ALIAS	= 0x0d,
+	JE_AREA		= 0x0e,
+
+	JE_LAST		= 0x0e,
+};
+
+#endif

fs/logfs/readwrite.c

···
+/*
+ * fs/logfs/readwrite.c
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ *
+ *
+ * Actually contains five sets of very similar functions:
+ * read		read blocks from a file
+ * seek_hole	find next hole
+ * seek_data	find next data block
+ * valid	check whether a block still belongs to a file
+ * write	write blocks to a file
+ * delete	delete a block (for directories and ifile)
+ * rewrite	move existing blocks of a file to a new location (gc helper)
+ * truncate	truncate a file
+ */
+#include "logfs.h"
+#include <linux/sched.h>
+
+static u64 adjust_bix(u64 bix, level_t level)
+{
+	switch (level) {
+	case 0:
+		return bix;
+	case LEVEL(1):
+		return max_t(u64, bix, I0_BLOCKS);
+	case LEVEL(2):
+		return max_t(u64, bix, I1_BLOCKS);
+	case LEVEL(3):
+		return max_t(u64, bix, I2_BLOCKS);
+	case LEVEL(4):
+		return max_t(u64, bix, I3_BLOCKS);
+	case LEVEL(5):
+		return max_t(u64, bix, I4_BLOCKS);
+	default:
+		WARN_ON(1);
+		return bix;
+	}
+}
+
+static inline u64 maxbix(u8 height)
+{
+	return 1ULL << (LOGFS_BLOCK_BITS * height);
+}
+
+/**
+ * The inode address space is cut in two halves.  Lower half belongs to data
+ * pages, upper half to indirect blocks.  If the high bit (INDIRECT_BIT) is
+ * set, the actual block index (bix) and level can be derived from the page
+ * index.
+ *
+ * The lowest three bits of the block index are set to 0 after packing and
+ * unpacking.  Since the lowest n bits (9 for 4KiB blocksize) are ignored
+ * anyway this is harmless.
+ */
+#define ARCH_SHIFT	(BITS_PER_LONG - 32)
+#define INDIRECT_BIT	(0x80000000UL << ARCH_SHIFT)
+#define LEVEL_SHIFT	(28 + ARCH_SHIFT)
+static inline pgoff_t first_indirect_block(void)
+{
+	return INDIRECT_BIT | (1ULL << LEVEL_SHIFT);
+}
+
+pgoff_t logfs_pack_index(u64 bix, level_t level)
+{
+	pgoff_t index;
+
+	BUG_ON(bix >= INDIRECT_BIT);
+	if (level == 0)
+		return bix;
+
+	index  = INDIRECT_BIT;
+	index |= (__force long)level << LEVEL_SHIFT;
+	index |= bix >> ((__force u8)level * LOGFS_BLOCK_BITS);
+	return index;
+}
+
+void logfs_unpack_index(pgoff_t index, u64 *bix, level_t *level)
+{
+	u8 __level;
+
+	if (!(index & INDIRECT_BIT)) {
+		*bix = index;
+		*level = 0;
+		return;
+	}
+
+	__level = (index & ~INDIRECT_BIT) >> LEVEL_SHIFT;
+	*level = LEVEL(__level);
+	*bix = (index << (__level * LOGFS_BLOCK_BITS)) & ~INDIRECT_BIT;
+	*bix = adjust_bix(*bix, *level);
+	return;
+}
+#undef ARCH_SHIFT
+#undef INDIRECT_BIT
+#undef LEVEL_SHIFT
+
+/*
+ * Time is stored as nanoseconds since the epoch.
+ */
+static struct timespec be64_to_timespec(__be64 betime)
+{
+	return ns_to_timespec(be64_to_cpu(betime));
+}
+
+static __be64 timespec_to_be64(struct timespec tsp)
+{
+	return cpu_to_be64((u64)tsp.tv_sec * NSEC_PER_SEC + tsp.tv_nsec);
+}
+
+static void logfs_disk_to_inode(struct logfs_disk_inode *di, struct inode*inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	inode->i_mode	= be16_to_cpu(di->di_mode);
+	li->li_height	= di->di_height;
+	li->li_flags	= be32_to_cpu(di->di_flags);
+	inode->i_uid	= be32_to_cpu(di->di_uid);
+	inode->i_gid	= be32_to_cpu(di->di_gid);
+	inode->i_size	= be64_to_cpu(di->di_size);
+	logfs_set_blocks(inode, be64_to_cpu(di->di_used_bytes));
+	inode->i_atime	= be64_to_timespec(di->di_atime);
+	inode->i_ctime	= be64_to_timespec(di->di_ctime);
+	inode->i_mtime	= be64_to_timespec(di->di_mtime);
+	inode->i_nlink	= be32_to_cpu(di->di_refcount);
+	inode->i_generation = be32_to_cpu(di->di_generation);
+
+	switch (inode->i_mode & S_IFMT) {
+	case S_IFSOCK:	/* fall through */
+	case S_IFBLK:	/* fall through */
+	case S_IFCHR:	/* fall through */
+	case S_IFIFO:
+		inode->i_rdev = be64_to_cpu(di->di_data[0]);
+		break;
+	case S_IFDIR:	/* fall through */
+	case S_IFREG:	/* fall through */
+	case S_IFLNK:
+		for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+			li->li_data[i] = be64_to_cpu(di->di_data[i]);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static void logfs_inode_to_disk(struct inode *inode, struct logfs_disk_inode*di)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	int i;
+
+	di->di_mode	= cpu_to_be16(inode->i_mode);
+	di->di_height	= li->li_height;
+	di->di_pad	= 0;
+	di->di_flags	= cpu_to_be32(li->li_flags);
+	di->di_uid	= cpu_to_be32(inode->i_uid);
+	di->di_gid	= cpu_to_be32(inode->i_gid);
+	di->di_size	= cpu_to_be64(i_size_read(inode));
+	di->di_used_bytes = cpu_to_be64(li->li_used_bytes);
+	di->di_atime	= timespec_to_be64(inode->i_atime);
+	di->di_ctime	= timespec_to_be64(inode->i_ctime);
+	di->di_mtime	= timespec_to_be64(inode->i_mtime);
+	di->di_refcount	= cpu_to_be32(inode->i_nlink);
+	di->di_generation = cpu_to_be32(inode->i_generation);
+
+	switch (inode->i_mode & S_IFMT) {
+	case S_IFSOCK:	/* fall through */
+	case S_IFBLK:	/* fall through */
+	case S_IFCHR:	/* fall through */
+	case S_IFIFO:
+		di->di_data[0] = cpu_to_be64(inode->i_rdev);
+		break;
+	case S_IFDIR:	/* fall through */
+	case S_IFREG:	/* fall through */
+	case S_IFLNK:
+		for (i = 0; i < LOGFS_EMBEDDED_FIELDS; i++)
+			di->di_data[i] = cpu_to_be64(li->li_data[i]);
+		break;
+	default:
+		BUG();
+	}
+}
+
+static void __logfs_set_blocks(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_inode *li = logfs_inode(inode);
+
+	inode->i_blocks = ULONG_MAX;
+	if (li->li_used_bytes >> sb->s_blocksize_bits < ULONG_MAX)
+		inode->i_blocks = ALIGN(li->li_used_bytes, 512) >> 9;
+}
+
+void logfs_set_blocks(struct inode *inode, u64 bytes)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	li->li_used_bytes = bytes;
+	__logfs_set_blocks(inode);
+}
+
+static void prelock_page(struct super_block *sb, struct page *page, int lock)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	BUG_ON(!PageLocked(page));
+	if (lock) {
+		BUG_ON(PagePreLocked(page));
+		SetPagePreLocked(page);
+	} else {
+		/* We are in GC path. */
+		if (PagePreLocked(page))
+			super->s_lock_count++;
+		else
+			SetPagePreLocked(page);
+	}
+}
+
+static void preunlock_page(struct super_block *sb, struct page *page, int lock)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	BUG_ON(!PageLocked(page));
+	if (lock)
+		ClearPagePreLocked(page);
+	else {
+		/* We are in GC path. */
+		BUG_ON(!PagePreLocked(page));
+		if (super->s_lock_count)
+			super->s_lock_count--;
+		else
+			ClearPagePreLocked(page);
+	}
+}
+
+/*
+ * Logfs is prone to an AB-BA deadlock where one task tries to acquire
+ * s_write_mutex with a locked page and GC tries to get that page while holding
+ * s_write_mutex.
+ * To solve this issue logfs will ignore the page lock iff the page in question
+ * is waiting for s_write_mutex.  We annotate this fact by setting PG_pre_locked
+ * in addition to PG_locked.
+ */
+static void logfs_get_wblocks(struct super_block *sb, struct page *page,
+		int lock)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	if (page)
+		prelock_page(sb, page, lock);
+
+	if (lock) {
+		mutex_lock(&super->s_write_mutex);
+		logfs_gc_pass(sb);
+		/* FIXME: We also have to check for shadowed space
+		 * and mempool fill grade */
+	}
+}
+
+static void logfs_put_wblocks(struct super_block *sb, struct page *page,
+		int lock)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	if (page)
+		preunlock_page(sb, page, lock);
+	/* Order matters - we must clear PG_pre_locked before releasing
+	 * s_write_mutex or we could race against another task. */
+	if (lock)
+		mutex_unlock(&super->s_write_mutex);
+}
+
+static struct page *logfs_get_read_page(struct inode *inode, u64 bix,
+		level_t level)
+{
+	return find_or_create_page(inode->i_mapping,
+			logfs_pack_index(bix, level), GFP_NOFS);
+}
+
+static void logfs_put_read_page(struct page *page)
+{
+	unlock_page(page);
+	page_cache_release(page);
+}
+
+static void logfs_lock_write_page(struct page *page)
+{
+	int loop = 0;
+
+	while (unlikely(!trylock_page(page))) {
+		if (loop++ > 0x1000) {
+			/* Has been observed once so far... */
+			printk(KERN_ERR "stack at %p\n", &loop);
+			BUG();
+		}
+		if (PagePreLocked(page)) {
+			/* Holder of page lock is waiting for us, it
+			 * is safe to use this page. */
+			break;
+		}
+		/* Some other process has this page locked and has
+		 * nothing to do with us.  Wait for it to finish.
+		 */
+		schedule();
+	}
+	BUG_ON(!PageLocked(page));
+}
+
+static struct page *logfs_get_write_page(struct inode *inode, u64 bix,
+		level_t level)
+{
+	struct address_space *mapping = inode->i_mapping;
+	pgoff_t index = logfs_pack_index(bix, level);
+	struct page *page;
+	int err;
+
+repeat:
+	page = find_get_page(mapping, index);
+	if (!page) {
+		page = __page_cache_alloc(GFP_NOFS);
+		if (!page)
+			return NULL;
+		err = add_to_page_cache_lru(page, mapping, index, GFP_NOFS);
+		if (unlikely(err)) {
+			page_cache_release(page);
+			if (err == -EEXIST)
+				goto repeat;
+			return NULL;
+		}
+	} else logfs_lock_write_page(page);
+	BUG_ON(!PageLocked(page));
+	return page;
+}
+
+static void logfs_unlock_write_page(struct page *page)
+{
+	if (!PagePreLocked(page))
+		unlock_page(page);
+}
+
+static void logfs_put_write_page(struct page *page)
+{
+	logfs_unlock_write_page(page);
+	page_cache_release(page);
+}
+
+static struct page *logfs_get_page(struct inode *inode, u64 bix, level_t level,
+		int rw)
+{
+	if (rw == READ)
+		return logfs_get_read_page(inode, bix, level);
+	else
+		return logfs_get_write_page(inode, bix, level);
+}
+
+static void logfs_put_page(struct page *page, int rw)
+{
+	if (rw == READ)
+		logfs_put_read_page(page);
+	else
+		logfs_put_write_page(page);
+}
+
+static unsigned long __get_bits(u64 val, int skip, int no)
+{
+	u64 ret = val;
+
+	ret >>= skip * no;
+	ret <<= 64 - no;
+	ret >>= 64 - no;
+	return ret;
+}
+
+static unsigned long get_bits(u64 val, level_t skip)
+{
+	return __get_bits(val, (__force int)skip, LOGFS_BLOCK_BITS);
+}
+
+static inline void init_shadow_tree(struct super_block *sb,
+		struct shadow_tree *tree)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	btree_init_mempool64(&tree->new, super->s_btree_pool);
+	btree_init_mempool64(&tree->old, super->s_btree_pool);
+}
+
+static void indirect_write_block(struct logfs_block *block)
+{
+	struct page *page;
+	struct inode *inode;
+	int ret;
+
+	page = block->page;
+	inode = page->mapping->host;
+	logfs_lock_write_page(page);
+	ret = logfs_write_buf(inode, page, 0);
+	logfs_unlock_write_page(page);
+	/*
+	 * This needs some rework.  Unless you want your filesystem to run
+	 * completely synchronously (you don't), the filesystem will always
+	 * report writes as 'successful' before the actual work has been
+	 * done.  The actual work gets done here and this is where any errors
+	 * will show up.  And there isn't much we can do about it, really.
+	 *
+	 * Some attempts to fix the errors (move from bad blocks, retry io,...)
+	 * have already been done, so anything left should be either a broken
+	 * device or a bug somewhere in logfs itself.  Being relatively new,
+	 * the odds currently favor a bug, so for now the line below isn't
+	 * entirely tasteles.
+	 */
+	BUG_ON(ret);
+}
+
+static void inode_write_block(struct logfs_block *block)
+{
+	struct inode *inode;
+	int ret;
+
+	inode = block->inode;
+	if (inode->i_ino == LOGFS_INO_MASTER)
+		logfs_write_anchor(inode);
+	else {
+		ret = __logfs_write_inode(inode, 0);
+		/* see indirect_write_block comment */
+		BUG_ON(ret);
+	}
+}
+
+static gc_level_t inode_block_level(struct logfs_block *block)
+{
+	BUG_ON(block->inode->i_ino == LOGFS_INO_MASTER);
+	return GC_LEVEL(LOGFS_MAX_LEVELS);
+}
+
+static gc_level_t indirect_block_level(struct logfs_block *block)
+{
+	struct page *page;
+	struct inode *inode;
+	u64 bix;
+	level_t level;
+
+	page = block->page;
+	inode = page->mapping->host;
+	logfs_unpack_index(page->index, &bix, &level);
+	return expand_level(inode->i_ino, level);
+}
+
+/*
+ * This silences a false, yet annoying gcc warning.  I hate it when my editor
+ * jumps into bitops.h each time I recompile this file.
+ * TODO: Complain to gcc folks about this and upgrade compiler.
+ */
+static unsigned long fnb(const unsigned long *addr,
+		unsigned long size, unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+
+static __be64 inode_val0(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	u64 val;
+
+	/*
+	 * Explicit shifting generates good code, but must match the format
+	 * of the structure.  Add some paranoia just in case.
+	 */
+	BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_mode) != 0);
+	BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_height) != 2);
+	BUILD_BUG_ON(offsetof(struct logfs_disk_inode, di_flags) != 4);
+
+	val =	(u64)inode->i_mode << 48 |
+		(u64)li->li_height << 40 |
+		(u64)li->li_flags;
+	return cpu_to_be64(val);
+}
+
+static int inode_write_alias(struct super_block *sb,
+		struct logfs_block *block, write_alias_t *write_one_alias)
+{
+	struct inode *inode = block->inode;
+	struct logfs_inode *li = logfs_inode(inode);
+	unsigned long pos;
+	u64 ino , bix;
+	__be64 val;
+	level_t level;
+	int err;
+
+	for (pos = 0; ; pos++) {
+		pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
+		if (pos >= LOGFS_EMBEDDED_FIELDS + INODE_POINTER_OFS)
+			return 0;
+
+		switch (pos) {
+		case INODE_HEIGHT_OFS:
+			val = inode_val0(inode);
+			break;
+		case INODE_USED_OFS:
+			val = cpu_to_be64(li->li_used_bytes);;
+			break;
+		case INODE_SIZE_OFS:
+			val = cpu_to_be64(i_size_read(inode));
+			break;
+		case INODE_POINTER_OFS ... INODE_POINTER_OFS + LOGFS_EMBEDDED_FIELDS - 1:
+			val = cpu_to_be64(li->li_data[pos - INODE_POINTER_OFS]);
+			break;
+		default:
+			BUG();
+		}
+
+		ino = LOGFS_INO_MASTER;
+		bix = inode->i_ino;
+		level = LEVEL(0);
+		err = write_one_alias(sb, ino, bix, level, pos, val);
+		if (err)
+			return err;
+	}
+}
+
+static int indirect_write_alias(struct super_block *sb,
+		struct logfs_block *block, write_alias_t *write_one_alias)
+{
+	unsigned long pos;
+	struct page *page = block->page;
+	u64 ino , bix;
+	__be64 *child, val;
+	level_t level;
+	int err;
+
+	for (pos = 0; ; pos++) {
+		pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
+		if (pos >= LOGFS_BLOCK_FACTOR)
+			return 0;
+
+		ino = page->mapping->host->i_ino;
+		logfs_unpack_index(page->index, &bix, &level);
+		child = kmap_atomic(page, KM_USER0);
+		val = child[pos];
+		kunmap_atomic(child, KM_USER0);
+		err = write_one_alias(sb, ino, bix, level, pos, val);
+		if (err)
+			return err;
+	}
+}
+
+int logfs_write_obj_aliases_pagecache(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_block *block;
+	int err;
+
+	list_for_each_entry(block, &super->s_object_alias, alias_list) {
+		err = block->ops->write_alias(sb, block, write_alias_journal);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+void __free_block(struct super_block *sb, struct logfs_block *block)
+{
+	BUG_ON(!list_empty(&block->item_list));
+	list_del(&block->alias_list);
+	mempool_free(block, logfs_super(sb)->s_block_pool);
+}
+
+static void inode_free_block(struct super_block *sb, struct logfs_block *block)
+{
+	struct inode *inode = block->inode;
+
+	logfs_inode(inode)->li_block = NULL;
+	__free_block(sb, block);
+}
+
+static void indirect_free_block(struct super_block *sb,
+		struct logfs_block *block)
+{
+	ClearPagePrivate(block->page);
+	block->page->private = 0;
+	__free_block(sb, block);
+}
+
+
+static struct logfs_block_ops inode_block_ops = {
+	.write_block = inode_write_block,
+	.block_level = inode_block_level,
+	.free_block = inode_free_block,
+	.write_alias = inode_write_alias,
+};
+
+struct logfs_block_ops indirect_block_ops = {
+	.write_block = indirect_write_block,
+	.block_level = indirect_block_level,
+	.free_block = indirect_free_block,
+	.write_alias = indirect_write_alias,
+};
+
+struct logfs_block *__alloc_block(struct super_block *sb,
+		u64 ino, u64 bix, level_t level)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_block *block;
+
+	block = mempool_alloc(super->s_block_pool, GFP_NOFS);
+	memset(block, 0, sizeof(*block));
+	INIT_LIST_HEAD(&block->alias_list);
+	INIT_LIST_HEAD(&block->item_list);
+	block->sb = sb;
+	block->ino = ino;
+	block->bix = bix;
+	block->level = level;
+	return block;
+}
+
+static void alloc_inode_block(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct logfs_block *block;
+
+	if (li->li_block)
+		return;
+
+	block = __alloc_block(inode->i_sb, LOGFS_INO_MASTER, inode->i_ino, 0);
+	block->inode = inode;
+	li->li_block = block;
+	block->ops = &inode_block_ops;
+}
+
+void initialize_block_counters(struct page *page, struct logfs_block *block,
+		__be64 *array, int page_is_empty)
+{
+	u64 ptr;
+	int i, start;
+
+	block->partial = 0;
+	block->full = 0;
+	start = 0;
+	if (page->index < first_indirect_block()) {
+		/* Counters are pointless on level 0 */
+		return;
+	}
+	if (page->index == first_indirect_block()) {
+		/* Skip unused pointers */
+		start = I0_BLOCKS;
+		block->full = I0_BLOCKS;
+	}
+	if (!page_is_empty) {
+		for (i = start; i < LOGFS_BLOCK_FACTOR; i++) {
+			ptr = be64_to_cpu(array[i]);
+			if (ptr)
+				block->partial++;
+			if (ptr & LOGFS_FULLY_POPULATED)
+				block->full++;
+		}
+	}
+}
+
+static void alloc_data_block(struct inode *inode, struct page *page)
+{
+	struct logfs_block *block;
+	u64 bix;
+	level_t level;
+
+	if (PagePrivate(page))
+		return;
+
+	logfs_unpack_index(page->index, &bix, &level);
+	block = __alloc_block(inode->i_sb, inode->i_ino, bix, level);
+	block->page = page;
+	SetPagePrivate(page);
+	page->private = (unsigned long)block;
+	block->ops = &indirect_block_ops;
+}
+
+static void alloc_indirect_block(struct inode *inode, struct page *page,
+		int page_is_empty)
+{
+	struct logfs_block *block;
+	__be64 *array;
+
+	if (PagePrivate(page))
+		return;
+
+	alloc_data_block(inode, page);
+
+	block = logfs_block(page);
+	array = kmap_atomic(page, KM_USER0);
+	initialize_block_counters(page, block, array, page_is_empty);
+	kunmap_atomic(array, KM_USER0);
+}
+
+static void block_set_pointer(struct page *page, int index, u64 ptr)
+{
+	struct logfs_block *block = logfs_block(page);
+	__be64 *array;
+	u64 oldptr;
+
+	BUG_ON(!block);
+	array = kmap_atomic(page, KM_USER0);
+	oldptr = be64_to_cpu(array[index]);
+	array[index] = cpu_to_be64(ptr);
+	kunmap_atomic(array, KM_USER0);
+	SetPageUptodate(page);
+
+	block->full += !!(ptr & LOGFS_FULLY_POPULATED)
+		- !!(oldptr & LOGFS_FULLY_POPULATED);
+	block->partial += !!ptr - !!oldptr;
+}
+
+static u64 block_get_pointer(struct page *page, int index)
+{
+	__be64 *block;
+	u64 ptr;
+
+	block = kmap_atomic(page, KM_USER0);
+	ptr = be64_to_cpu(block[index]);
+	kunmap_atomic(block, KM_USER0);
+	return ptr;
+}
+
+static int logfs_read_empty(struct page *page)
+{
+	zero_user_segment(page, 0, PAGE_CACHE_SIZE);
+	return 0;
+}
+
+static int logfs_read_direct(struct inode *inode, struct page *page)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	pgoff_t index = page->index;
+	u64 block;
+
+	block = li->li_data[index];
+	if (!block)
+		return logfs_read_empty(page);
+
+	return logfs_segment_read(inode, page, block, index, 0);
+}
+
+static int logfs_read_loop(struct inode *inode, struct page *page,
+		int rw_context)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	u64 bix, bofs = li->li_data[INDIRECT_INDEX];
+	level_t level, target_level;
+	int ret;
+	struct page *ipage;
+
+	logfs_unpack_index(page->index, &bix, &target_level);
+	if (!bofs)
+		return logfs_read_empty(page);
+
+	if (bix >= maxbix(li->li_height))
+		return logfs_read_empty(page);
+
+	for (level = LEVEL(li->li_height);
+			(__force u8)level > (__force u8)target_level;
+			level = SUBLEVEL(level)){
+		ipage = logfs_get_page(inode, bix, level, rw_context);
+		if (!ipage)
+			return -ENOMEM;
+
+		ret = logfs_segment_read(inode, ipage, bofs, bix, level);
+		if (ret) {
+			logfs_put_read_page(ipage);
+			return ret;
+		}
+
+		bofs = block_get_pointer(ipage, get_bits(bix, SUBLEVEL(level)));
+		logfs_put_page(ipage, rw_context);
+		if (!bofs)
+			return logfs_read_empty(page);
+	}
+
+	return logfs_segment_read(inode, page, bofs, bix, 0);
+}
+
+static int logfs_read_block(struct inode *inode, struct page *page,
+		int rw_context)
+{
+	pgoff_t index = page->index;
+
+	if (index < I0_BLOCKS)
+		return logfs_read_direct(inode, page);
+	return logfs_read_loop(inode, page, rw_context);
+}
+
+static int logfs_exist_loop(struct inode *inode, u64 bix)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	u64 bofs = li->li_data[INDIRECT_INDEX];
+	level_t level;
+	int ret;
+	struct page *ipage;
+
+	if (!bofs)
+		return 0;
+	if (bix >= maxbix(li->li_height))
+		return 0;
+
+	for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)) {
+		ipage = logfs_get_read_page(inode, bix, level);
+		if (!ipage)
+			return -ENOMEM;
+
+		ret = logfs_segment_read(inode, ipage, bofs, bix, level);
+		if (ret) {
+			logfs_put_read_page(ipage);
+			return ret;
+		}
+
+		bofs = block_get_pointer(ipage, get_bits(bix, SUBLEVEL(level)));
+		logfs_put_read_page(ipage);
+		if (!bofs)
+			return 0;
+	}
+
+	return 1;
+}
+
+int logfs_exist_block(struct inode *inode, u64 bix)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if (bix < I0_BLOCKS)
+		return !!li->li_data[bix];
+	return logfs_exist_loop(inode, bix);
+}
+
+static u64 seek_holedata_direct(struct inode *inode, u64 bix, int data)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	for (; bix < I0_BLOCKS; bix++)
+		if (data ^ (li->li_data[bix] == 0))
+			return bix;
+	return I0_BLOCKS;
+}
+
+static u64 seek_holedata_loop(struct inode *inode, u64 bix, int data)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	__be64 *rblock;
+	u64 increment, bofs = li->li_data[INDIRECT_INDEX];
+	level_t level;
+	int ret, slot;
+	struct page *page;
+
+	BUG_ON(!bofs);
+
+	for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)) {
+		increment = 1 << (LOGFS_BLOCK_BITS * ((__force u8)level-1));
+		page = logfs_get_read_page(inode, bix, level);
+		if (!page)
+			return bix;
+
+		ret = logfs_segment_read(inode, page, bofs, bix, level);
+		if (ret) {
+			logfs_put_read_page(page);
+			return bix;
+		}
+
+		slot = get_bits(bix, SUBLEVEL(level));
+		rblock = kmap_atomic(page, KM_USER0);
+		while (slot < LOGFS_BLOCK_FACTOR) {
+			if (data && (rblock[slot] != 0))
+				break;
+			if (!data && !(be64_to_cpu(rblock[slot]) & LOGFS_FULLY_POPULATED))
+				break;
+			slot++;
+			bix += increment;
+			bix &= ~(increment - 1);
+		}
+		if (slot >= LOGFS_BLOCK_FACTOR) {
+			kunmap_atomic(rblock, KM_USER0);
+			logfs_put_read_page(page);
+			return bix;
+		}
+		bofs = be64_to_cpu(rblock[slot]);
+		kunmap_atomic(rblock, KM_USER0);
+		logfs_put_read_page(page);
+		if (!bofs) {
+			BUG_ON(data);
+			return bix;
+		}
+	}
+	return bix;
+}
+
+/**
+ * logfs_seek_hole - find next hole starting at a given block index
+ * @inode:		inode to search in
+ * @bix:		block index to start searching
+ *
+ * Returns next hole.  If the file doesn't contain any further holes, the
+ * block address next to eof is returned instead.
+ */
+u64 logfs_seek_hole(struct inode *inode, u64 bix)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if (bix < I0_BLOCKS) {
+		bix = seek_holedata_direct(inode, bix, 0);
+		if (bix < I0_BLOCKS)
+			return bix;
+	}
+
+	if (!li->li_data[INDIRECT_INDEX])
+		return bix;
+	else if (li->li_data[INDIRECT_INDEX] & LOGFS_FULLY_POPULATED)
+		bix = maxbix(li->li_height);
+	else {
+		bix = seek_holedata_loop(inode, bix, 0);
+		if (bix < maxbix(li->li_height))
+			return bix;
+		/* Should not happen anymore.  But if some port writes semi-
+		 * corrupt images (as this one used to) we might run into it.
+		 */
+		WARN_ON_ONCE(bix == maxbix(li->li_height));
+	}
+
+	return bix;
+}
+
+static u64 __logfs_seek_data(struct inode *inode, u64 bix)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if (bix < I0_BLOCKS) {
+		bix = seek_holedata_direct(inode, bix, 1);
+		if (bix < I0_BLOCKS)
+			return bix;
+	}
+
+	if (bix < maxbix(li->li_height)) {
+		if (!li->li_data[INDIRECT_INDEX])
+			bix = maxbix(li->li_height);
+		else
+			return seek_holedata_loop(inode, bix, 1);
+	}
+
+	return bix;
+}
+
+/**
+ * logfs_seek_data - find next data block after a given block index
+ * @inode:		inode to search in
+ * @bix:		block index to start searching
+ *
+ * Returns next data block.  If the file doesn't contain any further data
+ * blocks, the last block in the file is returned instead.
+ */
+u64 logfs_seek_data(struct inode *inode, u64 bix)
+{
+	struct super_block *sb = inode->i_sb;
+	u64 ret, end;
+
+	ret = __logfs_seek_data(inode, bix);
+	end = i_size_read(inode) >> sb->s_blocksize_bits;
+	if (ret >= end)
+		ret = max(bix, end);
+	return ret;
+}
+
+static int logfs_is_valid_direct(struct logfs_inode *li, u64 bix, u64 ofs)
+{
+	return pure_ofs(li->li_data[bix]) == ofs;
+}
+
+static int __logfs_is_valid_loop(struct inode *inode, u64 bix,
+		u64 ofs, u64 bofs)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	level_t level;
+	int ret;
+	struct page *page;
+
+	for (level = LEVEL(li->li_height); level != 0; level = SUBLEVEL(level)){
+		page = logfs_get_write_page(inode, bix, level);
+		BUG_ON(!page);
+
+		ret = logfs_segment_read(inode, page, bofs, bix, level);
+		if (ret) {
+			logfs_put_write_page(page);
+			return 0;
+		}
+
+		bofs = block_get_pointer(page, get_bits(bix, SUBLEVEL(level)));
+		logfs_put_write_page(page);
+		if (!bofs)
+			return 0;
+
+		if (pure_ofs(bofs) == ofs)
+			return 1;
+	}
+	return 0;
+}
+
+static int logfs_is_valid_loop(struct inode *inode, u64 bix, u64 ofs)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	u64 bofs = li->li_data[INDIRECT_INDEX];
+
+	if (!bofs)
+		return 0;
+
+	if (bix >= maxbix(li->li_height))
+		return 0;
+
+	if (pure_ofs(bofs) == ofs)
+		return 1;
+
+	return __logfs_is_valid_loop(inode, bix, ofs, bofs);
+}
+
+static int __logfs_is_valid_block(struct inode *inode, u64 bix, u64 ofs)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if ((inode->i_nlink == 0) && atomic_read(&inode->i_count) == 1)
+		return 0;
+
+	if (bix < I0_BLOCKS)
+		return logfs_is_valid_direct(li, bix, ofs);
+	return logfs_is_valid_loop(inode, bix, ofs);
+}
+
+/**
+ * logfs_is_valid_block - check whether this block is still valid
+ *
+ * @sb	- superblock
+ * @ofs	- block physical offset
+ * @ino	- block inode number
+ * @bix	- block index
+ * @level - block level
+ *
+ * Returns 0 if the block is invalid, 1 if it is valid and 2 if it will
+ * become invalid once the journal is written.
+ */
+int logfs_is_valid_block(struct super_block *sb, u64 ofs, u64 ino, u64 bix,
+		gc_level_t gc_level)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode;
+	int ret, cookie;
+
+	/* Umount closes a segment with free blocks remaining.  Those
+	 * blocks are by definition invalid. */
+	if (ino == -1)
+		return 0;
+
+	LOGFS_BUG_ON((u64)(u_long)ino != ino, sb);
+
+	inode = logfs_safe_iget(sb, ino, &cookie);
+	if (IS_ERR(inode))
+		goto invalid;
+
+	ret = __logfs_is_valid_block(inode, bix, ofs);
+	logfs_safe_iput(inode, cookie);
+	if (ret)
+		return ret;
+
+invalid:
+	/* Block is nominally invalid, but may still sit in the shadow tree,
+	 * waiting for a journal commit.
+	 */
+	if (btree_lookup64(&super->s_shadow_tree.old, ofs))
+		return 2;
+	return 0;
+}
+
+int logfs_readpage_nolock(struct page *page)
+{
+	struct inode *inode = page->mapping->host;
+	int ret = -EIO;
+
+	ret = logfs_read_block(inode, page, READ);
+
+	if (ret) {
+		ClearPageUptodate(page);
+		SetPageError(page);
+	} else {
+		SetPageUptodate(page);
+		ClearPageError(page);
+	}
+	flush_dcache_page(page);
+
+	return ret;
+}
+
+static int logfs_reserve_bytes(struct inode *inode, int bytes)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	u64 available = super->s_free_bytes + super->s_dirty_free_bytes
+			- super->s_dirty_used_bytes - super->s_dirty_pages;
+
+	if (!bytes)
+		return 0;
+
+	if (available < bytes)
+		return -ENOSPC;
+
+	if (available < bytes + super->s_root_reserve &&
+			!capable(CAP_SYS_RESOURCE))
+		return -ENOSPC;
+
+	return 0;
+}
+
+int get_page_reserve(struct inode *inode, struct page *page)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	int ret;
+
+	if (logfs_block(page) && logfs_block(page)->reserved_bytes)
+		return 0;
+
+	logfs_get_wblocks(inode->i_sb, page, WF_LOCK);
+	ret = logfs_reserve_bytes(inode, 6 * LOGFS_MAX_OBJECTSIZE);
+	if (!ret) {
+		alloc_data_block(inode, page);
+		logfs_block(page)->reserved_bytes += 6 * LOGFS_MAX_OBJECTSIZE;
+		super->s_dirty_pages += 6 * LOGFS_MAX_OBJECTSIZE;
+	}
+	logfs_put_wblocks(inode->i_sb, page, WF_LOCK);
+	return ret;
+}
+
+/*
+ * We are protected by write lock.  Push victims up to superblock level
+ * and release transaction when appropriate.
+ */
+/* FIXME: This is currently called from the wrong spots. */
+static void logfs_handle_transaction(struct inode *inode,
+		struct logfs_transaction *ta)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+
+	if (!ta)
+		return;
+	logfs_inode(inode)->li_block->ta = NULL;
+
+	if (inode->i_ino != LOGFS_INO_MASTER) {
+		BUG(); /* FIXME: Yes, this needs more thought */
+		/* just remember the transaction until inode is written */
+		//BUG_ON(logfs_inode(inode)->li_transaction);
+		//logfs_inode(inode)->li_transaction = ta;
+		return;
+	}
+
+	switch (ta->state) {
+	case CREATE_1: /* fall through */
+	case UNLINK_1:
+		BUG_ON(super->s_victim_ino);
+		super->s_victim_ino = ta->ino;
+		break;
+	case CREATE_2: /* fall through */
+	case UNLINK_2:
+		BUG_ON(super->s_victim_ino != ta->ino);
+		super->s_victim_ino = 0;
+		/* transaction ends here - free it */
+		kfree(ta);
+		break;
+	case CROSS_RENAME_1:
+		BUG_ON(super->s_rename_dir);
+		BUG_ON(super->s_rename_pos);
+		super->s_rename_dir = ta->dir;
+		super->s_rename_pos = ta->pos;
+		break;
+	case CROSS_RENAME_2:
+		BUG_ON(super->s_rename_dir != ta->dir);
+		BUG_ON(super->s_rename_pos != ta->pos);
+		super->s_rename_dir = 0;
+		super->s_rename_pos = 0;
+		kfree(ta);
+		break;
+	case TARGET_RENAME_1:
+		BUG_ON(super->s_rename_dir);
+		BUG_ON(super->s_rename_pos);
+		BUG_ON(super->s_victim_ino);
+		super->s_rename_dir = ta->dir;
+		super->s_rename_pos = ta->pos;
+		super->s_victim_ino = ta->ino;
+		break;
+	case TARGET_RENAME_2:
+		BUG_ON(super->s_rename_dir != ta->dir);
+		BUG_ON(super->s_rename_pos != ta->pos);
+		BUG_ON(super->s_victim_ino != ta->ino);
+		super->s_rename_dir = 0;
+		super->s_rename_pos = 0;
+		break;
+	case TARGET_RENAME_3:
+		BUG_ON(super->s_rename_dir);
+		BUG_ON(super->s_rename_pos);
+		BUG_ON(super->s_victim_ino != ta->ino);
+		super->s_victim_ino = 0;
+		kfree(ta);
+		break;
+	default:
+		BUG();
+	}
+}
+
+/*
+ * Not strictly a reservation, but rather a check that we still have enough
+ * space to satisfy the write.
+ */
+static int logfs_reserve_blocks(struct inode *inode, int blocks)
+{
+	return logfs_reserve_bytes(inode, blocks * LOGFS_MAX_OBJECTSIZE);
+}
+
+struct write_control {
+	u64 ofs;
+	long flags;
+};
+
+static struct logfs_shadow *alloc_shadow(struct inode *inode, u64 bix,
+		level_t level, u64 old_ofs)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	struct logfs_shadow *shadow;
+
+	shadow = mempool_alloc(super->s_shadow_pool, GFP_NOFS);
+	memset(shadow, 0, sizeof(*shadow));
+	shadow->ino = inode->i_ino;
+	shadow->bix = bix;
+	shadow->gc_level = expand_level(inode->i_ino, level);
+	shadow->old_ofs = old_ofs & ~LOGFS_FULLY_POPULATED;
+	return shadow;
+}
+
+static void free_shadow(struct inode *inode, struct logfs_shadow *shadow)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+
+	mempool_free(shadow, super->s_shadow_pool);
+}
+
+/**
+ * fill_shadow_tree - Propagate shadow tree changes due to a write
+ * @inode:	Inode owning the page
+ * @page:	Struct page that was written
+ * @shadow:	Shadow for the current write
+ *
+ * Writes in logfs can result in two semi-valid objects.  The old object
+ * is still valid as long as it can be reached by following pointers on
+ * the medium.  Only when writes propagate all the way up to the journal
+ * has the new object safely replaced the old one.
+ *
+ * To handle this problem, a struct logfs_shadow is used to represent
+ * every single write.  It is attached to the indirect block, which is
+ * marked dirty.  When the indirect block is written, its shadows are
+ * handed up to the next indirect block (or inode).  Untimately they
+ * will reach the master inode and be freed upon journal commit.
+ *
+ * This function handles a single step in the propagation.  It adds the
+ * shadow for the current write to the tree, along with any shadows in
+ * the page's tree, in case it was an indirect block.  If a page is
+ * written, the inode parameter is left NULL, if an inode is written,
+ * the page parameter is left NULL.
+ */
+static void fill_shadow_tree(struct inode *inode, struct page *page,
+		struct logfs_shadow *shadow)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	struct logfs_block *block = logfs_block(page);
+	struct shadow_tree *tree = &super->s_shadow_tree;
+
+	if (PagePrivate(page)) {
+		if (block->alias_map)
+			super->s_no_object_aliases -= bitmap_weight(
+					block->alias_map, LOGFS_BLOCK_FACTOR);
+		logfs_handle_transaction(inode, block->ta);
+		block->ops->free_block(inode->i_sb, block);
+	}
+	if (shadow) {
+		if (shadow->old_ofs)
+			btree_insert64(&tree->old, shadow->old_ofs, shadow,
+					GFP_NOFS);
+		else
+			btree_insert64(&tree->new, shadow->new_ofs, shadow,
+					GFP_NOFS);
+
+		super->s_dirty_used_bytes += shadow->new_len;
+		super->s_dirty_free_bytes += shadow->old_len;
+	}
+}
+
+static void logfs_set_alias(struct super_block *sb, struct logfs_block *block,
+		long child_no)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	if (block->inode && block->inode->i_ino == LOGFS_INO_MASTER) {
+		/* Aliases in the master inode are pointless. */
+		return;
+	}
+
+	if (!test_bit(child_no, block->alias_map)) {
+		set_bit(child_no, block->alias_map);
+		super->s_no_object_aliases++;
+	}
+	list_move_tail(&block->alias_list, &super->s_object_alias);
+}
+
+/*
+ * Object aliases can and often do change the size and occupied space of a
+ * file.  So not only do we have to change the pointers, we also have to
+ * change inode->i_size and li->li_used_bytes.  Which is done by setting
+ * another two object aliases for the inode itself.
+ */
+static void set_iused(struct inode *inode, struct logfs_shadow *shadow)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if (shadow->new_len == shadow->old_len)
+		return;
+
+	alloc_inode_block(inode);
+	li->li_used_bytes += shadow->new_len - shadow->old_len;
+	__logfs_set_blocks(inode);
+	logfs_set_alias(inode->i_sb, li->li_block, INODE_USED_OFS);
+	logfs_set_alias(inode->i_sb, li->li_block, INODE_SIZE_OFS);
+}
+
+static int logfs_write_i0(struct inode *inode, struct page *page,
+		struct write_control *wc)
+{
+	struct logfs_shadow *shadow;
+	u64 bix;
+	level_t level;
+	int full, err = 0;
+
+	logfs_unpack_index(page->index, &bix, &level);
+	if (wc->ofs == 0)
+		if (logfs_reserve_blocks(inode, 1))
+			return -ENOSPC;
+
+	shadow = alloc_shadow(inode, bix, level, wc->ofs);
+	if (wc->flags & WF_WRITE)
+		err = logfs_segment_write(inode, page, shadow);
+	if (wc->flags & WF_DELETE)
+		logfs_segment_delete(inode, shadow);
+	if (err) {
+		free_shadow(inode, shadow);
+		return err;
+	}
+
+	set_iused(inode, shadow);
+	full = 1;
+	if (level != 0) {
+		alloc_indirect_block(inode, page, 0);
+		full = logfs_block(page)->full == LOGFS_BLOCK_FACTOR;
+	}
+	fill_shadow_tree(inode, page, shadow);
+	wc->ofs = shadow->new_ofs;
+	if (wc->ofs && full)
+		wc->ofs |= LOGFS_FULLY_POPULATED;
+	return 0;
+}
+
+static int logfs_write_direct(struct inode *inode, struct page *page,
+		long flags)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct write_control wc = {
+		.ofs = li->li_data[page->index],
+		.flags = flags,
+	};
+	int err;
+
+	alloc_inode_block(inode);
+
+	err = logfs_write_i0(inode, page, &wc);
+	if (err)
+		return err;
+
+	li->li_data[page->index] = wc.ofs;
+	logfs_set_alias(inode->i_sb, li->li_block,
+			page->index + INODE_POINTER_OFS);
+	return 0;
+}
+
+static int ptr_change(u64 ofs, struct page *page)
+{
+	struct logfs_block *block = logfs_block(page);
+	int empty0, empty1, full0, full1;
+
+	empty0 = ofs == 0;
+	empty1 = block->partial == 0;
+	if (empty0 != empty1)
+		return 1;
+
+	/* The !! is necessary to shrink result to int */
+	full0 = !!(ofs & LOGFS_FULLY_POPULATED);
+	full1 = block->full == LOGFS_BLOCK_FACTOR;
+	if (full0 != full1)
+		return 1;
+	return 0;
+}
+
+static int __logfs_write_rec(struct inode *inode, struct page *page,
+		struct write_control *this_wc,
+		pgoff_t bix, level_t target_level, level_t level)
+{
+	int ret, page_empty = 0;
+	int child_no = get_bits(bix, SUBLEVEL(level));
+	struct page *ipage;
+	struct write_control child_wc = {
+		.flags = this_wc->flags,
+	};
+
+	ipage = logfs_get_write_page(inode, bix, level);
+	if (!ipage)
+		return -ENOMEM;
+
+	if (this_wc->ofs) {
+		ret = logfs_segment_read(inode, ipage, this_wc->ofs, bix, level);
+		if (ret)
+			goto out;
+	} else if (!PageUptodate(ipage)) {
+		page_empty = 1;
+		logfs_read_empty(ipage);
+	}
+
+	child_wc.ofs = block_get_pointer(ipage, child_no);
+
+	if ((__force u8)level-1 > (__force u8)target_level)
+		ret = __logfs_write_rec(inode, page, &child_wc, bix,
+				target_level, SUBLEVEL(level));
+	else
+		ret = logfs_write_i0(inode, page, &child_wc);
+
+	if (ret)
+		goto out;
+
+	alloc_indirect_block(inode, ipage, page_empty);
+	block_set_pointer(ipage, child_no, child_wc.ofs);
+	/* FIXME: first condition seems superfluous */
+	if (child_wc.ofs || logfs_block(ipage)->partial)
+		this_wc->flags |= WF_WRITE;
+	/* the condition on this_wc->ofs ensures that we won't consume extra
+	 * space for indirect blocks in the future, which we cannot reserve */
+	if (!this_wc->ofs || ptr_change(this_wc->ofs, ipage))
+		ret = logfs_write_i0(inode, ipage, this_wc);
+	else
+		logfs_set_alias(inode->i_sb, logfs_block(ipage), child_no);
+out:
+	logfs_put_write_page(ipage);
+	return ret;
+}
+
+static int logfs_write_rec(struct inode *inode, struct page *page,
+		pgoff_t bix, level_t target_level, long flags)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct write_control wc = {
+		.ofs = li->li_data[INDIRECT_INDEX],
+		.flags = flags,
+	};
+	int ret;
+
+	alloc_inode_block(inode);
+
+	if (li->li_height > (__force u8)target_level)
+		ret = __logfs_write_rec(inode, page, &wc, bix, target_level,
+				LEVEL(li->li_height));
+	else
+		ret = logfs_write_i0(inode, page, &wc);
+	if (ret)
+		return ret;
+
+	if (li->li_data[INDIRECT_INDEX] != wc.ofs) {
+		li->li_data[INDIRECT_INDEX] = wc.ofs;
+		logfs_set_alias(inode->i_sb, li->li_block,
+				INDIRECT_INDEX + INODE_POINTER_OFS);
+	}
+	return ret;
+}
+
+void logfs_add_transaction(struct inode *inode, struct logfs_transaction *ta)
+{
+	alloc_inode_block(inode);
+	logfs_inode(inode)->li_block->ta = ta;
+}
+
+void logfs_del_transaction(struct inode *inode, struct logfs_transaction *ta)
+{
+	struct logfs_block *block = logfs_inode(inode)->li_block;
+
+	if (block && block->ta)
+		block->ta = NULL;
+}
+
+static int grow_inode(struct inode *inode, u64 bix, level_t level)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	u8 height = (__force u8)level;
+	struct page *page;
+	struct write_control wc = {
+		.flags = WF_WRITE,
+	};
+	int err;
+
+	BUG_ON(height > 5 || li->li_height > 5);
+	while (height > li->li_height || bix >= maxbix(li->li_height)) {
+		page = logfs_get_write_page(inode, I0_BLOCKS + 1,
+				LEVEL(li->li_height + 1));
+		if (!page)
+			return -ENOMEM;
+		logfs_read_empty(page);
+		alloc_indirect_block(inode, page, 1);
+		block_set_pointer(page, 0, li->li_data[INDIRECT_INDEX]);
+		err = logfs_write_i0(inode, page, &wc);
+		logfs_put_write_page(page);
+		if (err)
+			return err;
+		li->li_data[INDIRECT_INDEX] = wc.ofs;
+		wc.ofs = 0;
+		li->li_height++;
+		logfs_set_alias(inode->i_sb, li->li_block, INODE_HEIGHT_OFS);
+	}
+	return 0;
+}
+
+static int __logfs_write_buf(struct inode *inode, struct page *page, long flags)
+{
+	struct logfs_super *super = logfs_super(inode->i_sb);
+	pgoff_t index = page->index;
+	u64 bix;
+	level_t level;
+	int err;
+
+	flags |= WF_WRITE | WF_DELETE;
+	inode->i_ctime = inode->i_mtime = CURRENT_TIME;
+
+	logfs_unpack_index(index, &bix, &level);
+	if (logfs_block(page) && logfs_block(page)->reserved_bytes)
+		super->s_dirty_pages -= logfs_block(page)->reserved_bytes;
+
+	if (index < I0_BLOCKS)
+		return logfs_write_direct(inode, page, flags);
+
+	bix = adjust_bix(bix, level);
+	err = grow_inode(inode, bix, level);
+	if (err)
+		return err;
+	return logfs_write_rec(inode, page, bix, level, flags);
+}
+
+int logfs_write_buf(struct inode *inode, struct page *page, long flags)
+{
+	struct super_block *sb = inode->i_sb;
+	int ret;
+
+	logfs_get_wblocks(sb, page, flags & WF_LOCK);
+	ret = __logfs_write_buf(inode, page, flags);
+	logfs_put_wblocks(sb, page, flags & WF_LOCK);
+	return ret;
+}
+
+static int __logfs_delete(struct inode *inode, struct page *page)
+{
+	long flags = WF_DELETE;
+
+	inode->i_ctime = inode->i_mtime = CURRENT_TIME;
+
+	if (page->index < I0_BLOCKS)
+		return logfs_write_direct(inode, page, flags);
+	return logfs_write_rec(inode, page, page->index, 0, flags);
+}
+
+int logfs_delete(struct inode *inode, pgoff_t index,
+		struct shadow_tree *shadow_tree)
+{
+	struct super_block *sb = inode->i_sb;
+	struct page *page;
+	int ret;
+
+	page = logfs_get_read_page(inode, index, 0);
+	if (!page)
+		return -ENOMEM;
+
+	logfs_get_wblocks(sb, page, 1);
+	ret = __logfs_delete(inode, page);
+	logfs_put_wblocks(sb, page, 1);
+
+	logfs_put_read_page(page);
+
+	return ret;
+}
+
+/* Rewrite cannot mark the inode dirty but has to write it immediatly. */
+int logfs_rewrite_block(struct inode *inode, u64 bix, u64 ofs,
+		gc_level_t gc_level, long flags)
+{
+	level_t level = shrink_level(gc_level);
+	struct page *page;
+	int err;
+
+	page = logfs_get_write_page(inode, bix, level);
+	if (!page)
+		return -ENOMEM;
+
+	err = logfs_segment_read(inode, page, ofs, bix, level);
+	if (!err) {
+		if (level != 0)
+			alloc_indirect_block(inode, page, 0);
+		err = logfs_write_buf(inode, page, flags);
+	}
+	logfs_put_write_page(page);
+	return err;
+}
+
+static int truncate_data_block(struct inode *inode, struct page *page,
+		u64 ofs, struct logfs_shadow *shadow, u64 size)
+{
+	loff_t pageofs = page->index << inode->i_sb->s_blocksize_bits;
+	u64 bix;
+	level_t level;
+	int err;
+
+	/* Does truncation happen within this page? */
+	if (size <= pageofs || size - pageofs >= PAGE_SIZE)
+		return 0;
+
+	logfs_unpack_index(page->index, &bix, &level);
+	BUG_ON(level != 0);
+
+	err = logfs_segment_read(inode, page, ofs, bix, level);
+	if (err)
+		return err;
+
+	zero_user_segment(page, size - pageofs, PAGE_CACHE_SIZE);
+	return logfs_segment_write(inode, page, shadow);
+}
+
+static int logfs_truncate_i0(struct inode *inode, struct page *page,
+		struct write_control *wc, u64 size)
+{
+	struct logfs_shadow *shadow;
+	u64 bix;
+	level_t level;
+	int err = 0;
+
+	logfs_unpack_index(page->index, &bix, &level);
+	BUG_ON(level != 0);
+	shadow = alloc_shadow(inode, bix, level, wc->ofs);
+
+	err = truncate_data_block(inode, page, wc->ofs, shadow, size);
+	if (err) {
+		free_shadow(inode, shadow);
+		return err;
+	}
+
+	logfs_segment_delete(inode, shadow);
+	set_iused(inode, shadow);
+	fill_shadow_tree(inode, page, shadow);
+	wc->ofs = shadow->new_ofs;
+	return 0;
+}
+
+static int logfs_truncate_direct(struct inode *inode, u64 size)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct write_control wc;
+	struct page *page;
+	int e;
+	int err;
+
+	alloc_inode_block(inode);
+
+	for (e = I0_BLOCKS - 1; e >= 0; e--) {
+		if (size > (e+1) * LOGFS_BLOCKSIZE)
+			break;
+
+		wc.ofs = li->li_data[e];
+		if (!wc.ofs)
+			continue;
+
+		page = logfs_get_write_page(inode, e, 0);
+		if (!page)
+			return -ENOMEM;
+		err = logfs_segment_read(inode, page, wc.ofs, e, 0);
+		if (err) {
+			logfs_put_write_page(page);
+			return err;
+		}
+		err = logfs_truncate_i0(inode, page, &wc, size);
+		logfs_put_write_page(page);
+		if (err)
+			return err;
+
+		li->li_data[e] = wc.ofs;
+	}
+	return 0;
+}
+
+/* FIXME: these need to become per-sb once we support different blocksizes */
+static u64 __logfs_step[] = {
+	1,
+	I1_BLOCKS,
+	I2_BLOCKS,
+	I3_BLOCKS,
+};
+
+static u64 __logfs_start_index[] = {
+	I0_BLOCKS,
+	I1_BLOCKS,
+	I2_BLOCKS,
+	I3_BLOCKS
+};
+
+static inline u64 logfs_step(level_t level)
+{
+	return __logfs_step[(__force u8)level];
+}
+
+static inline u64 logfs_factor(u8 level)
+{
+	return __logfs_step[level] * LOGFS_BLOCKSIZE;
+}
+
+static inline u64 logfs_start_index(level_t level)
+{
+	return __logfs_start_index[(__force u8)level];
+}
+
+static void logfs_unpack_raw_index(pgoff_t index, u64 *bix, level_t *level)
+{
+	logfs_unpack_index(index, bix, level);
+	if (*bix <= logfs_start_index(SUBLEVEL(*level)))
+		*bix = 0;
+}
+
+static int __logfs_truncate_rec(struct inode *inode, struct page *ipage,
+		struct write_control *this_wc, u64 size)
+{
+	int truncate_happened = 0;
+	int e, err = 0;
+	u64 bix, child_bix, next_bix;
+	level_t level;
+	struct page *page;
+	struct write_control child_wc = { /* FIXME: flags */ };
+
+	logfs_unpack_raw_index(ipage->index, &bix, &level);
+	err = logfs_segment_read(inode, ipage, this_wc->ofs, bix, level);
+	if (err)
+		return err;
+
+	for (e = LOGFS_BLOCK_FACTOR - 1; e >= 0; e--) {
+		child_bix = bix + e * logfs_step(SUBLEVEL(level));
+		next_bix = child_bix + logfs_step(SUBLEVEL(level));
+		if (size > next_bix * LOGFS_BLOCKSIZE)
+			break;
+
+		child_wc.ofs = pure_ofs(block_get_pointer(ipage, e));
+		if (!child_wc.ofs)
+			continue;
+
+		page = logfs_get_write_page(inode, child_bix, SUBLEVEL(level));
+		if (!page)
+			return -ENOMEM;
+
+		if ((__force u8)level > 1)
+			err = __logfs_truncate_rec(inode, page, &child_wc, size);
+		else
+			err = logfs_truncate_i0(inode, page, &child_wc, size);
+		logfs_put_write_page(page);
+		if (err)
+			return err;
+
+		truncate_happened = 1;
+		alloc_indirect_block(inode, ipage, 0);
+		block_set_pointer(ipage, e, child_wc.ofs);
+	}
+
+	if (!truncate_happened) {
+		printk("ineffectual truncate (%lx, %lx, %llx)\n", inode->i_ino, ipage->index, size);
+		return 0;
+	}
+
+	this_wc->flags = WF_DELETE;
+	if (logfs_block(ipage)->partial)
+		this_wc->flags |= WF_WRITE;
+
+	return logfs_write_i0(inode, ipage, this_wc);
+}
+
+static int logfs_truncate_rec(struct inode *inode, u64 size)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct write_control wc = {
+		.ofs = li->li_data[INDIRECT_INDEX],
+	};
+	struct page *page;
+	int err;
+
+	alloc_inode_block(inode);
+
+	if (!wc.ofs)
+		return 0;
+
+	page = logfs_get_write_page(inode, 0, LEVEL(li->li_height));
+	if (!page)
+		return -ENOMEM;
+
+	err = __logfs_truncate_rec(inode, page, &wc, size);
+	logfs_put_write_page(page);
+	if (err)
+		return err;
+
+	if (li->li_data[INDIRECT_INDEX] != wc.ofs)
+		li->li_data[INDIRECT_INDEX] = wc.ofs;
+	return 0;
+}
+
+static int __logfs_truncate(struct inode *inode, u64 size)
+{
+	int ret;
+
+	if (size >= logfs_factor(logfs_inode(inode)->li_height))
+		return 0;
+
+	ret = logfs_truncate_rec(inode, size);
+	if (ret)
+		return ret;
+
+	return logfs_truncate_direct(inode, size);
+}
+
+int logfs_truncate(struct inode *inode, u64 size)
+{
+	struct super_block *sb = inode->i_sb;
+	int err;
+
+	logfs_get_wblocks(sb, NULL, 1);
+	err = __logfs_truncate(inode, size);
+	if (!err)
+		err = __logfs_write_inode(inode, 0);
+	logfs_put_wblocks(sb, NULL, 1);
+
+	if (!err)
+		err = vmtruncate(inode, size);
+
+	/* I don't trust error recovery yet. */
+	WARN_ON(err);
+	return err;
+}
+
+static void move_page_to_inode(struct inode *inode, struct page *page)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct logfs_block *block = logfs_block(page);
+
+	if (!block)
+		return;
+
+	log_blockmove("move_page_to_inode(%llx, %llx, %x)\n",
+			block->ino, block->bix, block->level);
+	BUG_ON(li->li_block);
+	block->ops = &inode_block_ops;
+	block->inode = inode;
+	li->li_block = block;
+
+	block->page = NULL;
+	page->private = 0;
+	ClearPagePrivate(page);
+}
+
+static void move_inode_to_page(struct page *page, struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+	struct logfs_block *block = li->li_block;
+
+	if (!block)
+		return;
+
+	log_blockmove("move_inode_to_page(%llx, %llx, %x)\n",
+			block->ino, block->bix, block->level);
+	BUG_ON(PagePrivate(page));
+	block->ops = &indirect_block_ops;
+	block->page = page;
+	page->private = (unsigned long)block;
+	SetPagePrivate(page);
+
+	block->inode = NULL;
+	li->li_block = NULL;
+}
+
+int logfs_read_inode(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *master_inode = super->s_master_inode;
+	struct page *page;
+	struct logfs_disk_inode *di;
+	u64 ino = inode->i_ino;
+
+	if (ino << sb->s_blocksize_bits > i_size_read(master_inode))
+		return -ENODATA;
+	if (!logfs_exist_block(master_inode, ino))
+		return -ENODATA;
+
+	page = read_cache_page(master_inode->i_mapping, ino,
+			(filler_t *)logfs_readpage, NULL);
+	if (IS_ERR(page))
+		return PTR_ERR(page);
+
+	di = kmap_atomic(page, KM_USER0);
+	logfs_disk_to_inode(di, inode);
+	kunmap_atomic(di, KM_USER0);
+	move_page_to_inode(inode, page);
+	page_cache_release(page);
+	return 0;
+}
+
+/* Caller must logfs_put_write_page(page); */
+static struct page *inode_to_page(struct inode *inode)
+{
+	struct inode *master_inode = logfs_super(inode->i_sb)->s_master_inode;
+	struct logfs_disk_inode *di;
+	struct page *page;
+
+	BUG_ON(inode->i_ino == LOGFS_INO_MASTER);
+
+	page = logfs_get_write_page(master_inode, inode->i_ino, 0);
+	if (!page)
+		return NULL;
+
+	di = kmap_atomic(page, KM_USER0);
+	logfs_inode_to_disk(inode, di);
+	kunmap_atomic(di, KM_USER0);
+	move_inode_to_page(page, inode);
+	return page;
+}
+
+/* Cheaper version of write_inode.  All changes are concealed in
+ * aliases, which are moved back.  No write to the medium happens.
+ */
+void logfs_clear_inode(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_inode *li = logfs_inode(inode);
+	struct logfs_block *block = li->li_block;
+	struct page *page;
+
+	/* Only deleted files may be dirty at this point */
+	BUG_ON(inode->i_state & I_DIRTY && inode->i_nlink);
+	if (!block)
+		return;
+	if ((logfs_super(sb)->s_flags & LOGFS_SB_FLAG_SHUTDOWN)) {
+		block->ops->free_block(inode->i_sb, block);
+		return;
+	}
+
+	BUG_ON(inode->i_ino < LOGFS_RESERVED_INOS);
+	page = inode_to_page(inode);
+	BUG_ON(!page); /* FIXME: Use emergency page */
+	logfs_put_write_page(page);
+}
+
+static int do_write_inode(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct inode *master_inode = logfs_super(sb)->s_master_inode;
+	loff_t size = (inode->i_ino + 1) << inode->i_sb->s_blocksize_bits;
+	struct page *page;
+	int err;
+
+	BUG_ON(inode->i_ino == LOGFS_INO_MASTER);
+	/* FIXME: lock inode */
+
+	if (i_size_read(master_inode) < size)
+		i_size_write(master_inode, size);
+
+	/* TODO: Tell vfs this inode is clean now */
+
+	page = inode_to_page(inode);
+	if (!page)
+		return -ENOMEM;
+
+	/* FIXME: transaction is part of logfs_block now.  Is that enough? */
+	err = logfs_write_buf(master_inode, page, 0);
+	logfs_put_write_page(page);
+	return err;
+}
+
+static void logfs_mod_segment_entry(struct super_block *sb, u32 segno,
+		int write,
+		void (*change_se)(struct logfs_segment_entry *, long),
+		long arg)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode;
+	struct page *page;
+	struct logfs_segment_entry *se;
+	pgoff_t page_no;
+	int child_no;
+
+	page_no = segno >> (sb->s_blocksize_bits - 3);
+	child_no = segno & ((sb->s_blocksize >> 3) - 1);
+
+	inode = super->s_segfile_inode;
+	page = logfs_get_write_page(inode, page_no, 0);
+	BUG_ON(!page); /* FIXME: We need some reserve page for this case */
+	if (!PageUptodate(page))
+		logfs_read_block(inode, page, WRITE);
+
+	if (write)
+		alloc_indirect_block(inode, page, 0);
+	se = kmap_atomic(page, KM_USER0);
+	change_se(se + child_no, arg);
+	if (write) {
+		logfs_set_alias(sb, logfs_block(page), child_no);
+		BUG_ON((int)be32_to_cpu(se[child_no].valid) > super->s_segsize);
+	}
+	kunmap_atomic(se, KM_USER0);
+
+	logfs_put_write_page(page);
+}
+
+static void __get_segment_entry(struct logfs_segment_entry *se, long _target)
+{
+	struct logfs_segment_entry *target = (void *)_target;
+
+	*target = *se;
+}
+
+void logfs_get_segment_entry(struct super_block *sb, u32 segno,
+		struct logfs_segment_entry *se)
+{
+	logfs_mod_segment_entry(sb, segno, 0, __get_segment_entry, (long)se);
+}
+
+static void __set_segment_used(struct logfs_segment_entry *se, long increment)
+{
+	u32 valid;
+
+	valid = be32_to_cpu(se->valid);
+	valid += increment;
+	se->valid = cpu_to_be32(valid);
+}
+
+void logfs_set_segment_used(struct super_block *sb, u64 ofs, int increment)
+{
+	struct logfs_super *super = logfs_super(sb);
+	u32 segno = ofs >> super->s_segshift;
+
+	if (!increment)
+		return;
+
+	logfs_mod_segment_entry(sb, segno, 1, __set_segment_used, increment);
+}
+
+static void __set_segment_erased(struct logfs_segment_entry *se, long ec_level)
+{
+	se->ec_level = cpu_to_be32(ec_level);
+}
+
+void logfs_set_segment_erased(struct super_block *sb, u32 segno, u32 ec,
+		gc_level_t gc_level)
+{
+	u32 ec_level = ec << 4 | (__force u8)gc_level;
+
+	logfs_mod_segment_entry(sb, segno, 1, __set_segment_erased, ec_level);
+}
+
+static void __set_segment_reserved(struct logfs_segment_entry *se, long ignore)
+{
+	se->valid = cpu_to_be32(RESERVED);
+}
+
+void logfs_set_segment_reserved(struct super_block *sb, u32 segno)
+{
+	logfs_mod_segment_entry(sb, segno, 1, __set_segment_reserved, 0);
+}
+
+static void __set_segment_unreserved(struct logfs_segment_entry *se,
+		long ec_level)
+{
+	se->valid = 0;
+	se->ec_level = cpu_to_be32(ec_level);
+}
+
+void logfs_set_segment_unreserved(struct super_block *sb, u32 segno, u32 ec)
+{
+	u32 ec_level = ec << 4;
+
+	logfs_mod_segment_entry(sb, segno, 1, __set_segment_unreserved,
+			ec_level);
+}
+
+int __logfs_write_inode(struct inode *inode, long flags)
+{
+	struct super_block *sb = inode->i_sb;
+	int ret;
+
+	logfs_get_wblocks(sb, NULL, flags & WF_LOCK);
+	ret = do_write_inode(inode);
+	logfs_put_wblocks(sb, NULL, flags & WF_LOCK);
+	return ret;
+}
+
+static int do_delete_inode(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+	struct inode *master_inode = logfs_super(sb)->s_master_inode;
+	struct page *page;
+	int ret;
+
+	page = logfs_get_write_page(master_inode, inode->i_ino, 0);
+	if (!page)
+		return -ENOMEM;
+
+	move_inode_to_page(page, inode);
+
+	logfs_get_wblocks(sb, page, 1);
+	ret = __logfs_delete(master_inode, page);
+	logfs_put_wblocks(sb, page, 1);
+
+	logfs_put_write_page(page);
+	return ret;
+}
+
+/*
+ * ZOMBIE inodes have already been deleted before and should remain dead,
+ * if it weren't for valid checking.  No need to kill them again here.
+ */
+void logfs_delete_inode(struct inode *inode)
+{
+	struct logfs_inode *li = logfs_inode(inode);
+
+	if (!(li->li_flags & LOGFS_IF_ZOMBIE)) {
+		li->li_flags |= LOGFS_IF_ZOMBIE;
+		if (i_size_read(inode) > 0)
+			logfs_truncate(inode, 0);
+		do_delete_inode(inode);
+	}
+	truncate_inode_pages(&inode->i_data, 0);
+	clear_inode(inode);
+}
+
+void btree_write_block(struct logfs_block *block)
+{
+	struct inode *inode;
+	struct page *page;
+	int err, cookie;
+
+	inode = logfs_safe_iget(block->sb, block->ino, &cookie);
+	page = logfs_get_write_page(inode, block->bix, block->level);
+
+	err = logfs_readpage_nolock(page);
+	BUG_ON(err);
+	BUG_ON(!PagePrivate(page));
+	BUG_ON(logfs_block(page) != block);
+	err = __logfs_write_buf(inode, page, 0);
+	BUG_ON(err);
+	BUG_ON(PagePrivate(page) || page->private);
+
+	logfs_put_write_page(page);
+	logfs_safe_iput(inode, cookie);
+}
+
+/**
+ * logfs_inode_write - write inode or dentry objects
+ *
+ * @inode:		parent inode (ifile or directory)
+ * @buf:		object to write (inode or dentry)
+ * @n:			object size
+ * @_pos:		object number (file position in blocks/objects)
+ * @flags:		write flags
+ * @lock:		0 if write lock is already taken, 1 otherwise
+ * @shadow_tree:	shadow below this inode
+ *
+ * FIXME: All caller of this put a 200-300 byte variable on the stack,
+ * only to call here and do a memcpy from that stack variable.  A good
+ * example of wasted performance and stack space.
+ */
+int logfs_inode_write(struct inode *inode, const void *buf, size_t count,
+		loff_t bix, long flags, struct shadow_tree *shadow_tree)
+{
+	loff_t pos = bix << inode->i_sb->s_blocksize_bits;
+	int err;
+	struct page *page;
+	void *pagebuf;
+
+	BUG_ON(pos & (LOGFS_BLOCKSIZE-1));
+	BUG_ON(count > LOGFS_BLOCKSIZE);
+	page = logfs_get_write_page(inode, bix, 0);
+	if (!page)
+		return -ENOMEM;
+
+	pagebuf = kmap_atomic(page, KM_USER0);
+	memcpy(pagebuf, buf, count);
+	flush_dcache_page(page);
+	kunmap_atomic(pagebuf, KM_USER0);
+
+	if (i_size_read(inode) < pos + LOGFS_BLOCKSIZE)
+		i_size_write(inode, pos + LOGFS_BLOCKSIZE);
+
+	err = logfs_write_buf(inode, page, flags);
+	logfs_put_write_page(page);
+	return err;
+}
+
+int logfs_open_segfile(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct inode *inode;
+
+	inode = logfs_read_meta_inode(sb, LOGFS_INO_SEGFILE);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+	super->s_segfile_inode = inode;
+	return 0;
+}
+
+int logfs_init_rw(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int min_fill = 3 * super->s_no_blocks;
+
+	INIT_LIST_HEAD(&super->s_object_alias);
+	mutex_init(&super->s_write_mutex);
+	super->s_block_pool = mempool_create_kmalloc_pool(min_fill,
+			sizeof(struct logfs_block));
+	super->s_shadow_pool = mempool_create_kmalloc_pool(min_fill,
+			sizeof(struct logfs_shadow));
+	return 0;
+}
+
+void logfs_cleanup_rw(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	destroy_meta_inode(super->s_segfile_inode);
+	if (super->s_block_pool)
+		mempool_destroy(super->s_block_pool);
+	if (super->s_shadow_pool)
+		mempool_destroy(super->s_shadow_pool);
+}

fs/logfs/segment.c

···
+/*
+ * fs/logfs/segment.c	- Handling the Object Store
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ *
+ * Object store or ostore makes up the complete device with exception of
+ * the superblock and journal areas.  Apart from its own metadata it stores
+ * three kinds of objects: inodes, dentries and blocks, both data and indirect.
+ */
+#include "logfs.h"
+
+static int logfs_mark_segment_bad(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct btree_head32 *head = &super->s_reserved_segments;
+	int err;
+
+	err = btree_insert32(head, segno, (void *)1, GFP_NOFS);
+	if (err)
+		return err;
+	logfs_super(sb)->s_bad_segments++;
+	/* FIXME: write to journal */
+	return 0;
+}
+
+int logfs_erase_segment(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	super->s_gec++;
+
+	return super->s_devops->erase(sb, (u64)segno << super->s_segshift,
+			super->s_segsize);
+}
+
+static s64 logfs_get_free_bytes(struct logfs_area *area, size_t bytes)
+{
+	s32 ofs;
+
+	logfs_open_area(area, bytes);
+
+	ofs = area->a_used_bytes;
+	area->a_used_bytes += bytes;
+	BUG_ON(area->a_used_bytes >= logfs_super(area->a_sb)->s_segsize);
+
+	return dev_ofs(area->a_sb, area->a_segno, ofs);
+}
+
+static struct page *get_mapping_page(struct super_block *sb, pgoff_t index,
+		int use_filler)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	filler_t *filler = super->s_devops->readpage;
+	struct page *page;
+
+	BUG_ON(mapping_gfp_mask(mapping) & __GFP_FS);
+	if (use_filler)
+		page = read_cache_page(mapping, index, filler, sb);
+	else {
+		page = find_or_create_page(mapping, index, GFP_NOFS);
+		unlock_page(page);
+	}
+	return page;
+}
+
+void __logfs_buf_write(struct logfs_area *area, u64 ofs, void *buf, size_t len,
+		int use_filler)
+{
+	pgoff_t index = ofs >> PAGE_SHIFT;
+	struct page *page;
+	long offset = ofs & (PAGE_SIZE-1);
+	long copylen;
+
+	/* Only logfs_wbuf_recover may use len==0 */
+	BUG_ON(!len && !use_filler);
+	do {
+		copylen = min((ulong)len, PAGE_SIZE - offset);
+
+		page = get_mapping_page(area->a_sb, index, use_filler);
+		SetPageUptodate(page);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memcpy(page_address(page) + offset, buf, copylen);
+		SetPagePrivate(page);
+		page_cache_release(page);
+
+		buf += copylen;
+		len -= copylen;
+		offset = 0;
+		index++;
+	} while (len);
+}
+
+/*
+ * bdev_writeseg will write full pages.  Memset the tail to prevent data leaks.
+ */
+static void pad_wbuf(struct logfs_area *area, int final)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct page *page;
+	u64 ofs = dev_ofs(sb, area->a_segno, area->a_used_bytes);
+	pgoff_t index = ofs >> PAGE_SHIFT;
+	long offset = ofs & (PAGE_SIZE-1);
+	u32 len = PAGE_SIZE - offset;
+
+	if (len == PAGE_SIZE) {
+		/* The math in this function can surely use some love */
+		len = 0;
+	}
+	if (len) {
+		BUG_ON(area->a_used_bytes >= super->s_segsize);
+
+		page = get_mapping_page(area->a_sb, index, 0);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memset(page_address(page) + offset, 0xff, len);
+		SetPagePrivate(page);
+		page_cache_release(page);
+	}
+
+	if (!final)
+		return;
+
+	area->a_used_bytes += len;
+	for ( ; area->a_used_bytes < super->s_segsize;
+			area->a_used_bytes += PAGE_SIZE) {
+		/* Memset another page */
+		index++;
+		page = get_mapping_page(area->a_sb, index, 0);
+		BUG_ON(!page); /* FIXME: reserve a pool */
+		memset(page_address(page), 0xff, PAGE_SIZE);
+		SetPagePrivate(page);
+		page_cache_release(page);
+	}
+}
+
+/*
+ * We have to be careful with the alias tree.  Since lookup is done by bix,
+ * it needs to be normalized, so 14, 15, 16, etc. all match when dealing with
+ * indirect blocks.  So always use it through accessor functions.
+ */
+static void *alias_tree_lookup(struct super_block *sb, u64 ino, u64 bix,
+		level_t level)
+{
+	struct btree_head128 *head = &logfs_super(sb)->s_object_alias_tree;
+	pgoff_t index = logfs_pack_index(bix, level);
+
+	return btree_lookup128(head, ino, index);
+}
+
+static int alias_tree_insert(struct super_block *sb, u64 ino, u64 bix,
+		level_t level, void *val)
+{
+	struct btree_head128 *head = &logfs_super(sb)->s_object_alias_tree;
+	pgoff_t index = logfs_pack_index(bix, level);
+
+	return btree_insert128(head, ino, index, val, GFP_NOFS);
+}
+
+static int btree_write_alias(struct super_block *sb, struct logfs_block *block,
+		write_alias_t *write_one_alias)
+{
+	struct object_alias_item *item;
+	int err;
+
+	list_for_each_entry(item, &block->item_list, list) {
+		err = write_alias_journal(sb, block->ino, block->bix,
+				block->level, item->child_no, item->val);
+		if (err)
+			return err;
+	}
+	return 0;
+}
+
+static gc_level_t btree_block_level(struct logfs_block *block)
+{
+	return expand_level(block->ino, block->level);
+}
+
+static struct logfs_block_ops btree_block_ops = {
+	.write_block	= btree_write_block,
+	.block_level	= btree_block_level,
+	.free_block	= __free_block,
+	.write_alias	= btree_write_alias,
+};
+
+int logfs_load_object_aliases(struct super_block *sb,
+		struct logfs_obj_alias *oa, int count)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_block *block;
+	struct object_alias_item *item;
+	u64 ino, bix;
+	level_t level;
+	int i, err;
+
+	super->s_flags |= LOGFS_SB_FLAG_OBJ_ALIAS;
+	count /= sizeof(*oa);
+	for (i = 0; i < count; i++) {
+		item = mempool_alloc(super->s_alias_pool, GFP_NOFS);
+		if (!item)
+			return -ENOMEM;
+		memset(item, 0, sizeof(*item));
+
+		super->s_no_object_aliases++;
+		item->val = oa[i].val;
+		item->child_no = be16_to_cpu(oa[i].child_no);
+
+		ino = be64_to_cpu(oa[i].ino);
+		bix = be64_to_cpu(oa[i].bix);
+		level = LEVEL(oa[i].level);
+
+		log_aliases("logfs_load_object_aliases(%llx, %llx, %x, %x) %llx\n",
+				ino, bix, level, item->child_no,
+				be64_to_cpu(item->val));
+		block = alias_tree_lookup(sb, ino, bix, level);
+		if (!block) {
+			block = __alloc_block(sb, ino, bix, level);
+			block->ops = &btree_block_ops;
+			err = alias_tree_insert(sb, ino, bix, level, block);
+			BUG_ON(err); /* mempool empty */
+		}
+		if (test_and_set_bit(item->child_no, block->alias_map)) {
+			printk(KERN_ERR"LogFS: Alias collision detected\n");
+			return -EIO;
+		}
+		list_move_tail(&block->alias_list, &super->s_object_alias);
+		list_add(&item->list, &block->item_list);
+	}
+	return 0;
+}
+
+static void kill_alias(void *_block, unsigned long ignore0,
+		u64 ignore1, u64 ignore2, size_t ignore3)
+{
+	struct logfs_block *block = _block;
+	struct super_block *sb = block->sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct object_alias_item *item;
+
+	while (!list_empty(&block->item_list)) {
+		item = list_entry(block->item_list.next, typeof(*item), list);
+		list_del(&item->list);
+		mempool_free(item, super->s_alias_pool);
+	}
+	block->ops->free_block(sb, block);
+}
+
+static int obj_type(struct inode *inode, level_t level)
+{
+	if (level == 0) {
+		if (S_ISDIR(inode->i_mode))
+			return OBJ_DENTRY;
+		if (inode->i_ino == LOGFS_INO_MASTER)
+			return OBJ_INODE;
+	}
+	return OBJ_BLOCK;
+}
+
+static int obj_len(struct super_block *sb, int obj_type)
+{
+	switch (obj_type) {
+	case OBJ_DENTRY:
+		return sizeof(struct logfs_disk_dentry);
+	case OBJ_INODE:
+		return sizeof(struct logfs_disk_inode);
+	case OBJ_BLOCK:
+		return sb->s_blocksize;
+	default:
+		BUG();
+	}
+}
+
+static int __logfs_segment_write(struct inode *inode, void *buf,
+		struct logfs_shadow *shadow, int type, int len, int compr)
+{
+	struct logfs_area *area;
+	struct super_block *sb = inode->i_sb;
+	s64 ofs;
+	struct logfs_object_header h;
+	int acc_len;
+
+	if (shadow->gc_level == 0)
+		acc_len = len;
+	else
+		acc_len = obj_len(sb, type);
+
+	area = get_area(sb, shadow->gc_level);
+	ofs = logfs_get_free_bytes(area, len + LOGFS_OBJECT_HEADERSIZE);
+	LOGFS_BUG_ON(ofs <= 0, sb);
+	/*
+	 * Order is important.  logfs_get_free_bytes(), by modifying the
+	 * segment file, may modify the content of the very page we're about
+	 * to write now.  Which is fine, as long as the calculated crc and
+	 * written data still match.  So do the modifications _before_
+	 * calculating the crc.
+	 */
+
+	h.len	= cpu_to_be16(len);
+	h.type	= type;
+	h.compr	= compr;
+	h.ino	= cpu_to_be64(inode->i_ino);
+	h.bix	= cpu_to_be64(shadow->bix);
+	h.crc	= logfs_crc32(&h, sizeof(h) - 4, 4);
+	h.data_crc = logfs_crc32(buf, len, 0);
+
+	logfs_buf_write(area, ofs, &h, sizeof(h));
+	logfs_buf_write(area, ofs + LOGFS_OBJECT_HEADERSIZE, buf, len);
+
+	shadow->new_ofs = ofs;
+	shadow->new_len = acc_len + LOGFS_OBJECT_HEADERSIZE;
+
+	return 0;
+}
+
+static s64 logfs_segment_write_compress(struct inode *inode, void *buf,
+		struct logfs_shadow *shadow, int type, int len)
+{
+	struct super_block *sb = inode->i_sb;
+	void *compressor_buf = logfs_super(sb)->s_compressed_je;
+	ssize_t compr_len;
+	int ret;
+
+	mutex_lock(&logfs_super(sb)->s_journal_mutex);
+	compr_len = logfs_compress(buf, compressor_buf, len, len);
+
+	if (compr_len >= 0) {
+		ret = __logfs_segment_write(inode, compressor_buf, shadow,
+				type, compr_len, COMPR_ZLIB);
+	} else {
+		ret = __logfs_segment_write(inode, buf, shadow, type, len,
+				COMPR_NONE);
+	}
+	mutex_unlock(&logfs_super(sb)->s_journal_mutex);
+	return ret;
+}
+
+/**
+ * logfs_segment_write - write data block to object store
+ * @inode:		inode containing data
+ *
+ * Returns an errno or zero.
+ */
+int logfs_segment_write(struct inode *inode, struct page *page,
+		struct logfs_shadow *shadow)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_super *super = logfs_super(sb);
+	int do_compress, type, len;
+	int ret;
+	void *buf;
+
+	BUG_ON(logfs_super(sb)->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
+	do_compress = logfs_inode(inode)->li_flags & LOGFS_IF_COMPRESSED;
+	if (shadow->gc_level != 0) {
+		/* temporarily disable compression for indirect blocks */
+		do_compress = 0;
+	}
+
+	type = obj_type(inode, shrink_level(shadow->gc_level));
+	len = obj_len(sb, type);
+	buf = kmap(page);
+	if (do_compress)
+		ret = logfs_segment_write_compress(inode, buf, shadow, type,
+				len);
+	else
+		ret = __logfs_segment_write(inode, buf, shadow, type, len,
+				COMPR_NONE);
+	kunmap(page);
+
+	log_segment("logfs_segment_write(%llx, %llx, %x) %llx->%llx %x->%x\n",
+			shadow->ino, shadow->bix, shadow->gc_level,
+			shadow->old_ofs, shadow->new_ofs,
+			shadow->old_len, shadow->new_len);
+	/* this BUG_ON did catch a locking bug.  useful */
+	BUG_ON(!(shadow->new_ofs & (super->s_segsize - 1)));
+	return ret;
+}
+
+int wbuf_read(struct super_block *sb, u64 ofs, size_t len, void *buf)
+{
+	pgoff_t index = ofs >> PAGE_SHIFT;
+	struct page *page;
+	long offset = ofs & (PAGE_SIZE-1);
+	long copylen;
+
+	while (len) {
+		copylen = min((ulong)len, PAGE_SIZE - offset);
+
+		page = get_mapping_page(sb, index, 1);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+		memcpy(buf, page_address(page) + offset, copylen);
+		page_cache_release(page);
+
+		buf += copylen;
+		len -= copylen;
+		offset = 0;
+		index++;
+	}
+	return 0;
+}
+
+/*
+ * The "position" of indirect blocks is ambiguous.  It can be the position
+ * of any data block somewhere behind this indirect block.  So we need to
+ * normalize the positions through logfs_block_mask() before comparing.
+ */
+static int check_pos(struct super_block *sb, u64 pos1, u64 pos2, level_t level)
+{
+	return	(pos1 & logfs_block_mask(sb, level)) !=
+		(pos2 & logfs_block_mask(sb, level));
+}
+
+#if 0
+static int read_seg_header(struct super_block *sb, u64 ofs,
+		struct logfs_segment_header *sh)
+{
+	__be32 crc;
+	int err;
+
+	err = wbuf_read(sb, ofs, sizeof(*sh), sh);
+	if (err)
+		return err;
+	crc = logfs_crc32(sh, sizeof(*sh), 4);
+	if (crc != sh->crc) {
+		printk(KERN_ERR"LOGFS: header crc error at %llx: expected %x, "
+				"got %x\n", ofs, be32_to_cpu(sh->crc),
+				be32_to_cpu(crc));
+		return -EIO;
+	}
+	return 0;
+}
+#endif
+
+static int read_obj_header(struct super_block *sb, u64 ofs,
+		struct logfs_object_header *oh)
+{
+	__be32 crc;
+	int err;
+
+	err = wbuf_read(sb, ofs, sizeof(*oh), oh);
+	if (err)
+		return err;
+	crc = logfs_crc32(oh, sizeof(*oh) - 4, 4);
+	if (crc != oh->crc) {
+		printk(KERN_ERR"LOGFS: header crc error at %llx: expected %x, "
+				"got %x\n", ofs, be32_to_cpu(oh->crc),
+				be32_to_cpu(crc));
+		return -EIO;
+	}
+	return 0;
+}
+
+static void move_btree_to_page(struct inode *inode, struct page *page,
+		__be64 *data)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct btree_head128 *head = &super->s_object_alias_tree;
+	struct logfs_block *block;
+	struct object_alias_item *item, *next;
+
+	if (!(super->s_flags & LOGFS_SB_FLAG_OBJ_ALIAS))
+		return;
+
+	block = btree_remove128(head, inode->i_ino, page->index);
+	if (!block)
+		return;
+
+	log_blockmove("move_btree_to_page(%llx, %llx, %x)\n",
+			block->ino, block->bix, block->level);
+	list_for_each_entry_safe(item, next, &block->item_list, list) {
+		data[item->child_no] = item->val;
+		list_del(&item->list);
+		mempool_free(item, super->s_alias_pool);
+	}
+	block->page = page;
+	SetPagePrivate(page);
+	page->private = (unsigned long)block;
+	block->ops = &indirect_block_ops;
+	initialize_block_counters(page, block, data, 0);
+}
+
+/*
+ * This silences a false, yet annoying gcc warning.  I hate it when my editor
+ * jumps into bitops.h each time I recompile this file.
+ * TODO: Complain to gcc folks about this and upgrade compiler.
+ */
+static unsigned long fnb(const unsigned long *addr,
+		unsigned long size, unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+
+void move_page_to_btree(struct page *page)
+{
+	struct logfs_block *block = logfs_block(page);
+	struct super_block *sb = block->sb;
+	struct logfs_super *super = logfs_super(sb);
+	struct object_alias_item *item;
+	unsigned long pos;
+	__be64 *child;
+	int err;
+
+	if (super->s_flags & LOGFS_SB_FLAG_SHUTDOWN) {
+		block->ops->free_block(sb, block);
+		return;
+	}
+	log_blockmove("move_page_to_btree(%llx, %llx, %x)\n",
+			block->ino, block->bix, block->level);
+	super->s_flags |= LOGFS_SB_FLAG_OBJ_ALIAS;
+
+	for (pos = 0; ; pos++) {
+		pos = fnb(block->alias_map, LOGFS_BLOCK_FACTOR, pos);
+		if (pos >= LOGFS_BLOCK_FACTOR)
+			break;
+
+		item = mempool_alloc(super->s_alias_pool, GFP_NOFS);
+		BUG_ON(!item); /* mempool empty */
+		memset(item, 0, sizeof(*item));
+
+		child = kmap_atomic(page, KM_USER0);
+		item->val = child[pos];
+		kunmap_atomic(child, KM_USER0);
+		item->child_no = pos;
+		list_add(&item->list, &block->item_list);
+	}
+	block->page = NULL;
+	ClearPagePrivate(page);
+	page->private = 0;
+	block->ops = &btree_block_ops;
+	err = alias_tree_insert(block->sb, block->ino, block->bix, block->level,
+			block);
+	BUG_ON(err); /* mempool empty */
+	ClearPageUptodate(page);
+}
+
+static int __logfs_segment_read(struct inode *inode, void *buf,
+		u64 ofs, u64 bix, level_t level)
+{
+	struct super_block *sb = inode->i_sb;
+	void *compressor_buf = logfs_super(sb)->s_compressed_je;
+	struct logfs_object_header oh;
+	__be32 crc;
+	u16 len;
+	int err, block_len;
+
+	block_len = obj_len(sb, obj_type(inode, level));
+	err = read_obj_header(sb, ofs, &oh);
+	if (err)
+		goto out_err;
+
+	err = -EIO;
+	if (be64_to_cpu(oh.ino) != inode->i_ino
+			|| check_pos(sb, be64_to_cpu(oh.bix), bix, level)) {
+		printk(KERN_ERR"LOGFS: (ino, bix) don't match at %llx: "
+				"expected (%lx, %llx), got (%llx, %llx)\n",
+				ofs, inode->i_ino, bix,
+				be64_to_cpu(oh.ino), be64_to_cpu(oh.bix));
+		goto out_err;
+	}
+
+	len = be16_to_cpu(oh.len);
+
+	switch (oh.compr) {
+	case COMPR_NONE:
+		err = wbuf_read(sb, ofs + LOGFS_OBJECT_HEADERSIZE, len, buf);
+		if (err)
+			goto out_err;
+		crc = logfs_crc32(buf, len, 0);
+		if (crc != oh.data_crc) {
+			printk(KERN_ERR"LOGFS: uncompressed data crc error at "
+					"%llx: expected %x, got %x\n", ofs,
+					be32_to_cpu(oh.data_crc),
+					be32_to_cpu(crc));
+			goto out_err;
+		}
+		break;
+	case COMPR_ZLIB:
+		mutex_lock(&logfs_super(sb)->s_journal_mutex);
+		err = wbuf_read(sb, ofs + LOGFS_OBJECT_HEADERSIZE, len,
+				compressor_buf);
+		if (err) {
+			mutex_unlock(&logfs_super(sb)->s_journal_mutex);
+			goto out_err;
+		}
+		crc = logfs_crc32(compressor_buf, len, 0);
+		if (crc != oh.data_crc) {
+			printk(KERN_ERR"LOGFS: compressed data crc error at "
+					"%llx: expected %x, got %x\n", ofs,
+					be32_to_cpu(oh.data_crc),
+					be32_to_cpu(crc));
+			mutex_unlock(&logfs_super(sb)->s_journal_mutex);
+			goto out_err;
+		}
+		err = logfs_uncompress(compressor_buf, buf, len, block_len);
+		mutex_unlock(&logfs_super(sb)->s_journal_mutex);
+		if (err) {
+			printk(KERN_ERR"LOGFS: uncompress error at %llx\n", ofs);
+			goto out_err;
+		}
+		break;
+	default:
+		LOGFS_BUG(sb);
+		err = -EIO;
+		goto out_err;
+	}
+	return 0;
+
+out_err:
+	logfs_set_ro(sb);
+	printk(KERN_ERR"LOGFS: device is read-only now\n");
+	LOGFS_BUG(sb);
+	return err;
+}
+
+/**
+ * logfs_segment_read - read data block from object store
+ * @inode:		inode containing data
+ * @buf:		data buffer
+ * @ofs:		physical data offset
+ * @bix:		block index
+ * @level:		block level
+ *
+ * Returns 0 on success or a negative errno.
+ */
+int logfs_segment_read(struct inode *inode, struct page *page,
+		u64 ofs, u64 bix, level_t level)
+{
+	int err;
+	void *buf;
+
+	if (PageUptodate(page))
+		return 0;
+
+	ofs &= ~LOGFS_FULLY_POPULATED;
+
+	buf = kmap(page);
+	err = __logfs_segment_read(inode, buf, ofs, bix, level);
+	if (!err) {
+		move_btree_to_page(inode, page, buf);
+		SetPageUptodate(page);
+	}
+	kunmap(page);
+	log_segment("logfs_segment_read(%lx, %llx, %x) %llx (%d)\n",
+			inode->i_ino, bix, level, ofs, err);
+	return err;
+}
+
+int logfs_segment_delete(struct inode *inode, struct logfs_shadow *shadow)
+{
+	struct super_block *sb = inode->i_sb;
+	struct logfs_object_header h;
+	u16 len;
+	int err;
+
+	BUG_ON(logfs_super(sb)->s_flags & LOGFS_SB_FLAG_SHUTDOWN);
+	BUG_ON(shadow->old_ofs & LOGFS_FULLY_POPULATED);
+	if (!shadow->old_ofs)
+		return 0;
+
+	log_segment("logfs_segment_delete(%llx, %llx, %x) %llx->%llx %x->%x\n",
+			shadow->ino, shadow->bix, shadow->gc_level,
+			shadow->old_ofs, shadow->new_ofs,
+			shadow->old_len, shadow->new_len);
+	err = read_obj_header(sb, shadow->old_ofs, &h);
+	LOGFS_BUG_ON(err, sb);
+	LOGFS_BUG_ON(be64_to_cpu(h.ino) != inode->i_ino, sb);
+	LOGFS_BUG_ON(check_pos(sb, shadow->bix, be64_to_cpu(h.bix),
+				shrink_level(shadow->gc_level)), sb);
+
+	if (shadow->gc_level == 0)
+		len = be16_to_cpu(h.len);
+	else
+		len = obj_len(sb, h.type);
+	shadow->old_len = len + sizeof(h);
+	return 0;
+}
+
+static void freeseg(struct super_block *sb, u32 segno)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping = super->s_mapping_inode->i_mapping;
+	struct page *page;
+	u64 ofs, start, end;
+
+	start = dev_ofs(sb, segno, 0);
+	end = dev_ofs(sb, segno + 1, 0);
+	for (ofs = start; ofs < end; ofs += PAGE_SIZE) {
+		page = find_get_page(mapping, ofs >> PAGE_SHIFT);
+		if (!page)
+			continue;
+		ClearPagePrivate(page);
+		page_cache_release(page);
+	}
+}
+
+int logfs_open_area(struct logfs_area *area, size_t bytes)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_super *super = logfs_super(sb);
+	int err, closed = 0;
+
+	if (area->a_is_open && area->a_used_bytes + bytes <= super->s_segsize)
+		return 0;
+
+	if (area->a_is_open) {
+		u64 ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
+		u32 len = super->s_segsize - area->a_written_bytes;
+
+		log_gc("logfs_close_area(%x)\n", area->a_segno);
+		pad_wbuf(area, 1);
+		super->s_devops->writeseg(area->a_sb, ofs, len);
+		freeseg(sb, area->a_segno);
+		closed = 1;
+	}
+
+	area->a_used_bytes = 0;
+	area->a_written_bytes = 0;
+again:
+	area->a_ops->get_free_segment(area);
+	area->a_ops->get_erase_count(area);
+
+	log_gc("logfs_open_area(%x, %x)\n", area->a_segno, area->a_level);
+	err = area->a_ops->erase_segment(area);
+	if (err) {
+		printk(KERN_WARNING "LogFS: Error erasing segment %x\n",
+				area->a_segno);
+		logfs_mark_segment_bad(sb, area->a_segno);
+		goto again;
+	}
+	area->a_is_open = 1;
+	return closed;
+}
+
+void logfs_sync_area(struct logfs_area *area)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_super *super = logfs_super(sb);
+	u64 ofs = dev_ofs(sb, area->a_segno, area->a_written_bytes);
+	u32 len = (area->a_used_bytes - area->a_written_bytes);
+
+	if (super->s_writesize)
+		len &= ~(super->s_writesize - 1);
+	if (len == 0)
+		return;
+	pad_wbuf(area, 0);
+	super->s_devops->writeseg(sb, ofs, len);
+	area->a_written_bytes += len;
+}
+
+void logfs_sync_segments(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	for_each_area(i)
+		logfs_sync_area(super->s_area[i]);
+}
+
+/*
+ * Pick a free segment to be used for this area.  Effectively takes a
+ * candidate from the free list (not really a candidate anymore).
+ */
+static void ostore_get_free_segment(struct logfs_area *area)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_super *super = logfs_super(sb);
+
+	if (super->s_free_list.count == 0) {
+		printk(KERN_ERR"LOGFS: ran out of free segments\n");
+		LOGFS_BUG(sb);
+	}
+
+	area->a_segno = get_best_cand(sb, &super->s_free_list, NULL);
+}
+
+static void ostore_get_erase_count(struct logfs_area *area)
+{
+	struct logfs_segment_entry se;
+	u32 ec_level;
+
+	logfs_get_segment_entry(area->a_sb, area->a_segno, &se);
+	BUG_ON(se.ec_level == cpu_to_be32(BADSEG) ||
+			se.valid == cpu_to_be32(RESERVED));
+
+	ec_level = be32_to_cpu(se.ec_level);
+	area->a_erase_count = (ec_level >> 4) + 1;
+}
+
+static int ostore_erase_segment(struct logfs_area *area)
+{
+	struct super_block *sb = area->a_sb;
+	struct logfs_segment_header sh;
+	u64 ofs;
+	int err;
+
+	err = logfs_erase_segment(sb, area->a_segno);
+	if (err)
+		return err;
+
+	sh.pad = 0;
+	sh.type = SEG_OSTORE;
+	sh.level = (__force u8)area->a_level;
+	sh.segno = cpu_to_be32(area->a_segno);
+	sh.ec = cpu_to_be32(area->a_erase_count);
+	sh.gec = cpu_to_be64(logfs_super(sb)->s_gec);
+	sh.crc = logfs_crc32(&sh, sizeof(sh), 4);
+
+	logfs_set_segment_erased(sb, area->a_segno, area->a_erase_count,
+			area->a_level);
+
+	ofs = dev_ofs(sb, area->a_segno, 0);
+	area->a_used_bytes = sizeof(sh);
+	logfs_buf_write(area, ofs, &sh, sizeof(sh));
+	return 0;
+}
+
+static const struct logfs_area_ops ostore_area_ops = {
+	.get_free_segment	= ostore_get_free_segment,
+	.get_erase_count	= ostore_get_erase_count,
+	.erase_segment		= ostore_erase_segment,
+};
+
+static void free_area(struct logfs_area *area)
+{
+	if (area)
+		freeseg(area->a_sb, area->a_segno);
+	kfree(area);
+}
+
+static struct logfs_area *alloc_area(struct super_block *sb)
+{
+	struct logfs_area *area;
+
+	area = kzalloc(sizeof(*area), GFP_KERNEL);
+	if (!area)
+		return NULL;
+
+	area->a_sb = sb;
+	return area;
+}
+
+static void map_invalidatepage(struct page *page, unsigned long l)
+{
+	BUG();
+}
+
+static int map_releasepage(struct page *page, gfp_t g)
+{
+	/* Don't release these pages */
+	return 0;
+}
+
+static const struct address_space_operations mapping_aops = {
+	.invalidatepage = map_invalidatepage,
+	.releasepage	= map_releasepage,
+	.set_page_dirty = __set_page_dirty_nobuffers,
+};
+
+int logfs_init_mapping(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct address_space *mapping;
+	struct inode *inode;
+
+	inode = logfs_new_meta_inode(sb, LOGFS_INO_MAPPING);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+	super->s_mapping_inode = inode;
+	mapping = inode->i_mapping;
+	mapping->a_ops = &mapping_aops;
+	/* Would it be possible to use __GFP_HIGHMEM as well? */
+	mapping_set_gfp_mask(mapping, GFP_NOFS);
+	return 0;
+}
+
+int logfs_init_areas(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i = -1;
+
+	super->s_alias_pool = mempool_create_kmalloc_pool(600,
+			sizeof(struct object_alias_item));
+	if (!super->s_alias_pool)
+		return -ENOMEM;
+
+	super->s_journal_area = alloc_area(sb);
+	if (!super->s_journal_area)
+		goto err;
+
+	for_each_area(i) {
+		super->s_area[i] = alloc_area(sb);
+		if (!super->s_area[i])
+			goto err;
+		super->s_area[i]->a_level = GC_LEVEL(i);
+		super->s_area[i]->a_ops = &ostore_area_ops;
+	}
+	btree_init_mempool128(&super->s_object_alias_tree,
+			super->s_btree_pool);
+	return 0;
+
+err:
+	for (i--; i >= 0; i--)
+		free_area(super->s_area[i]);
+	free_area(super->s_journal_area);
+	mempool_destroy(super->s_alias_pool);
+	return -ENOMEM;
+}
+
+void logfs_cleanup_areas(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int i;
+
+	btree_grim_visitor128(&super->s_object_alias_tree, 0, kill_alias);
+	for_each_area(i)
+		free_area(super->s_area[i]);
+	free_area(super->s_journal_area);
+	destroy_meta_inode(super->s_mapping_inode);
+}

fs/logfs/super.c

···
+/*
+ * fs/logfs/super.c
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2005-2008 Joern Engel <[e-mail]>
+ *
+ * Generally contains mount/umount code and also serves as a dump area for
+ * any functions that don't fit elsewhere and neither justify a file of their
+ * own.
+ */
+#include "logfs.h"
+#include <linux/bio.h>
+#include <linux/mtd/mtd.h>
+#include <linux/statfs.h>
+#include <linux/buffer_head.h>
+
+static DEFINE_MUTEX(emergency_mutex);
+static struct page *emergency_page;
+
+struct page *emergency_read_begin(struct address_space *mapping, pgoff_t index)
+{
+	filler_t *filler = (filler_t *)mapping->a_ops->readpage;
+	struct page *page;
+	int err;
+
+	page = read_cache_page(mapping, index, filler, NULL);
+	if (page)
+		return page;
+
+	/* No more pages available, switch to emergency page */
+	printk(KERN_INFO"Logfs: Using emergency page\n");
+	mutex_lock(&emergency_mutex);
+	err = filler(NULL, emergency_page);
+	if (err) {
+		mutex_unlock(&emergency_mutex);
+		printk(KERN_EMERG"Logfs: Error reading emergency page\n");
+		return ERR_PTR(err);
+	}
+	return emergency_page;
+}
+
+void emergency_read_end(struct page *page)
+{
+	if (page == emergency_page)
+		mutex_unlock(&emergency_mutex);
+	else
+		page_cache_release(page);
+}
+
+static void dump_segfile(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_segment_entry se;
+	u32 segno;
+
+	for (segno = 0; segno < super->s_no_segs; segno++) {
+		logfs_get_segment_entry(sb, segno, &se);
+		printk("%3x: %6x %8x", segno, be32_to_cpu(se.ec_level),
+				be32_to_cpu(se.valid));
+		if (++segno < super->s_no_segs) {
+			logfs_get_segment_entry(sb, segno, &se);
+			printk(" %6x %8x", be32_to_cpu(se.ec_level),
+					be32_to_cpu(se.valid));
+		}
+		if (++segno < super->s_no_segs) {
+			logfs_get_segment_entry(sb, segno, &se);
+			printk(" %6x %8x", be32_to_cpu(se.ec_level),
+					be32_to_cpu(se.valid));
+		}
+		if (++segno < super->s_no_segs) {
+			logfs_get_segment_entry(sb, segno, &se);
+			printk(" %6x %8x", be32_to_cpu(se.ec_level),
+					be32_to_cpu(se.valid));
+		}
+		printk("\n");
+	}
+}
+
+/*
+ * logfs_crash_dump - dump debug information to device
+ *
+ * The LogFS superblock only occupies part of a segment.  This function will
+ * write as much debug information as it can gather into the spare space.
+ */
+void logfs_crash_dump(struct super_block *sb)
+{
+	dump_segfile(sb);
+}
+
+/*
+ * TODO: move to lib/string.c
+ */
+/**
+ * memchr_inv - Find a character in an area of memory.
+ * @s: The memory area
+ * @c: The byte to search for
+ * @n: The size of the area.
+ *
+ * returns the address of the first character other than @c, or %NULL
+ * if the whole buffer contains just @c.
+ */
+void *memchr_inv(const void *s, int c, size_t n)
+{
+	const unsigned char *p = s;
+	while (n-- != 0)
+		if ((unsigned char)c != *p++)
+			return (void *)(p - 1);
+
+	return NULL;
+}
+
+/*
+ * FIXME: There should be a reserve for root, similar to ext2.
+ */
+int logfs_statfs(struct dentry *dentry, struct kstatfs *stats)
+{
+	struct super_block *sb = dentry->d_sb;
+	struct logfs_super *super = logfs_super(sb);
+
+	stats->f_type		= LOGFS_MAGIC_U32;
+	stats->f_bsize		= sb->s_blocksize;
+	stats->f_blocks		= super->s_size >> LOGFS_BLOCK_BITS >> 3;
+	stats->f_bfree		= super->s_free_bytes >> sb->s_blocksize_bits;
+	stats->f_bavail		= super->s_free_bytes >> sb->s_blocksize_bits;
+	stats->f_files		= 0;
+	stats->f_ffree		= 0;
+	stats->f_namelen	= LOGFS_MAX_NAMELEN;
+	return 0;
+}
+
+static int logfs_sb_set(struct super_block *sb, void *_super)
+{
+	struct logfs_super *super = _super;
+
+	sb->s_fs_info = super;
+	sb->s_mtd = super->s_mtd;
+	sb->s_bdev = super->s_bdev;
+	return 0;
+}
+
+static int logfs_sb_test(struct super_block *sb, void *_super)
+{
+	struct logfs_super *super = _super;
+	struct mtd_info *mtd = super->s_mtd;
+
+	if (mtd && sb->s_mtd == mtd)
+		return 1;
+	if (super->s_bdev && sb->s_bdev == super->s_bdev)
+		return 1;
+	return 0;
+}
+
+static void set_segment_header(struct logfs_segment_header *sh, u8 type,
+		u8 level, u32 segno, u32 ec)
+{
+	sh->pad = 0;
+	sh->type = type;
+	sh->level = level;
+	sh->segno = cpu_to_be32(segno);
+	sh->ec = cpu_to_be32(ec);
+	sh->gec = cpu_to_be64(segno);
+	sh->crc = logfs_crc32(sh, LOGFS_SEGMENT_HEADERSIZE, 4);
+}
+
+static void logfs_write_ds(struct super_block *sb, struct logfs_disk_super *ds,
+		u32 segno, u32 ec)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_segment_header *sh = &ds->ds_sh;
+	int i;
+
+	memset(ds, 0, sizeof(*ds));
+	set_segment_header(sh, SEG_SUPER, 0, segno, ec);
+
+	ds->ds_ifile_levels	= super->s_ifile_levels;
+	ds->ds_iblock_levels	= super->s_iblock_levels;
+	ds->ds_data_levels	= super->s_data_levels; /* XXX: Remove */
+	ds->ds_segment_shift	= super->s_segshift;
+	ds->ds_block_shift	= sb->s_blocksize_bits;
+	ds->ds_write_shift	= super->s_writeshift;
+	ds->ds_filesystem_size	= cpu_to_be64(super->s_size);
+	ds->ds_segment_size	= cpu_to_be32(super->s_segsize);
+	ds->ds_bad_seg_reserve	= cpu_to_be32(super->s_bad_seg_reserve);
+	ds->ds_feature_incompat	= cpu_to_be64(super->s_feature_incompat);
+	ds->ds_feature_ro_compat= cpu_to_be64(super->s_feature_ro_compat);
+	ds->ds_feature_compat	= cpu_to_be64(super->s_feature_compat);
+	ds->ds_feature_flags	= cpu_to_be64(super->s_feature_flags);
+	ds->ds_root_reserve	= cpu_to_be64(super->s_root_reserve);
+	ds->ds_speed_reserve	= cpu_to_be64(super->s_speed_reserve);
+	journal_for_each(i)
+		ds->ds_journal_seg[i] = cpu_to_be32(super->s_journal_seg[i]);
+	ds->ds_magic		= cpu_to_be64(LOGFS_MAGIC);
+	ds->ds_crc = logfs_crc32(ds, sizeof(*ds),
+			LOGFS_SEGMENT_HEADERSIZE + 12);
+}
+
+static int write_one_sb(struct super_block *sb,
+		struct page *(*find_sb)(struct super_block *sb, u64 *ofs))
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_disk_super *ds;
+	struct logfs_segment_entry se;
+	struct page *page;
+	u64 ofs;
+	u32 ec, segno;
+	int err;
+
+	page = find_sb(sb, &ofs);
+	if (!page)
+		return -EIO;
+	ds = page_address(page);
+	segno = seg_no(sb, ofs);
+	logfs_get_segment_entry(sb, segno, &se);
+	ec = be32_to_cpu(se.ec_level) >> 4;
+	ec++;
+	logfs_set_segment_erased(sb, segno, ec, 0);
+	logfs_write_ds(sb, ds, segno, ec);
+	err = super->s_devops->write_sb(sb, page);
+	page_cache_release(page);
+	return err;
+}
+
+int logfs_write_sb(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int err;
+
+	/* First superblock */
+	err = write_one_sb(sb, super->s_devops->find_first_sb);
+	if (err)
+		return err;
+
+	/* Last superblock */
+	err = write_one_sb(sb, super->s_devops->find_last_sb);
+	if (err)
+		return err;
+	return 0;
+}
+
+static int ds_cmp(const void *ds0, const void *ds1)
+{
+	size_t len = sizeof(struct logfs_disk_super);
+
+	/* We know the segment headers differ, so ignore them */
+	len -= LOGFS_SEGMENT_HEADERSIZE;
+	ds0 += LOGFS_SEGMENT_HEADERSIZE;
+	ds1 += LOGFS_SEGMENT_HEADERSIZE;
+	return memcmp(ds0, ds1, len);
+}
+
+static int logfs_recover_sb(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct logfs_disk_super _ds0, *ds0 = &_ds0;
+	struct logfs_disk_super _ds1, *ds1 = &_ds1;
+	int err, valid0, valid1;
+
+	/* read first superblock */
+	err = wbuf_read(sb, super->s_sb_ofs[0], sizeof(*ds0), ds0);
+	if (err)
+		return err;
+	/* read last superblock */
+	err = wbuf_read(sb, super->s_sb_ofs[1], sizeof(*ds1), ds1);
+	if (err)
+		return err;
+	valid0 = logfs_check_ds(ds0) == 0;
+	valid1 = logfs_check_ds(ds1) == 0;
+
+	if (!valid0 && valid1) {
+		printk(KERN_INFO"First superblock is invalid - fixing.\n");
+		return write_one_sb(sb, super->s_devops->find_first_sb);
+	}
+	if (valid0 && !valid1) {
+		printk(KERN_INFO"Last superblock is invalid - fixing.\n");
+		return write_one_sb(sb, super->s_devops->find_last_sb);
+	}
+	if (valid0 && valid1 && ds_cmp(ds0, ds1)) {
+		printk(KERN_INFO"Superblocks don't match - fixing.\n");
+		return write_one_sb(sb, super->s_devops->find_last_sb);
+	}
+	/* If neither is valid now, something's wrong.  Didn't we properly
+	 * check them before?!? */
+	BUG_ON(!valid0 && !valid1);
+	return 0;
+}
+
+static int logfs_make_writeable(struct super_block *sb)
+{
+	int err;
+
+	/* Repair any broken superblock copies */
+	err = logfs_recover_sb(sb);
+	if (err)
+		return err;
+
+	/* Check areas for trailing unaccounted data */
+	err = logfs_check_areas(sb);
+	if (err)
+		return err;
+
+	err = logfs_open_segfile(sb);
+	if (err)
+		return err;
+
+	/* Do one GC pass before any data gets dirtied */
+	logfs_gc_pass(sb);
+
+	/* after all initializations are done, replay the journal
+	 * for rw-mounts, if necessary */
+	err = logfs_replay_journal(sb);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int logfs_get_sb_final(struct super_block *sb, struct vfsmount *mnt)
+{
+	struct inode *rootdir;
+	int err;
+
+	/* root dir */
+	rootdir = logfs_iget(sb, LOGFS_INO_ROOT);
+	if (IS_ERR(rootdir))
+		goto fail;
+
+	sb->s_root = d_alloc_root(rootdir);
+	if (!sb->s_root)
+		goto fail;
+
+	/* FIXME: check for read-only mounts */
+	err = logfs_make_writeable(sb);
+	if (err)
+		goto fail2;
+
+	log_super("LogFS: Finished mounting\n");
+	simple_set_mnt(mnt, sb);
+	return 0;
+
+fail2:
+	iput(rootdir);
+fail:
+	iput(logfs_super(sb)->s_master_inode);
+	return -EIO;
+}
+
+int logfs_check_ds(struct logfs_disk_super *ds)
+{
+	struct logfs_segment_header *sh = &ds->ds_sh;
+
+	if (ds->ds_magic != cpu_to_be64(LOGFS_MAGIC))
+		return -EINVAL;
+	if (sh->crc != logfs_crc32(sh, LOGFS_SEGMENT_HEADERSIZE, 4))
+		return -EINVAL;
+	if (ds->ds_crc != logfs_crc32(ds, sizeof(*ds),
+				LOGFS_SEGMENT_HEADERSIZE + 12))
+		return -EINVAL;
+	return 0;
+}
+
+static struct page *find_super_block(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct page *first, *last;
+
+	first = super->s_devops->find_first_sb(sb, &super->s_sb_ofs[0]);
+	if (!first || IS_ERR(first))
+		return NULL;
+	last = super->s_devops->find_last_sb(sb, &super->s_sb_ofs[1]);
+	if (!last || IS_ERR(first)) {
+		page_cache_release(first);
+		return NULL;
+	}
+
+	if (!logfs_check_ds(page_address(first))) {
+		page_cache_release(last);
+		return first;
+	}
+
+	/* First one didn't work, try the second superblock */
+	if (!logfs_check_ds(page_address(last))) {
+		page_cache_release(first);
+		return last;
+	}
+
+	/* Neither worked, sorry folks */
+	page_cache_release(first);
+	page_cache_release(last);
+	return NULL;
+}
+
+static int __logfs_read_sb(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	struct page *page;
+	struct logfs_disk_super *ds;
+	int i;
+
+	page = find_super_block(sb);
+	if (!page)
+		return -EIO;
+
+	ds = page_address(page);
+	super->s_size = be64_to_cpu(ds->ds_filesystem_size);
+	super->s_root_reserve = be64_to_cpu(ds->ds_root_reserve);
+	super->s_speed_reserve = be64_to_cpu(ds->ds_speed_reserve);
+	super->s_bad_seg_reserve = be32_to_cpu(ds->ds_bad_seg_reserve);
+	super->s_segsize = 1 << ds->ds_segment_shift;
+	super->s_segmask = (1 << ds->ds_segment_shift) - 1;
+	super->s_segshift = ds->ds_segment_shift;
+	sb->s_blocksize = 1 << ds->ds_block_shift;
+	sb->s_blocksize_bits = ds->ds_block_shift;
+	super->s_writesize = 1 << ds->ds_write_shift;
+	super->s_writeshift = ds->ds_write_shift;
+	super->s_no_segs = super->s_size >> super->s_segshift;
+	super->s_no_blocks = super->s_segsize >> sb->s_blocksize_bits;
+	super->s_feature_incompat = be64_to_cpu(ds->ds_feature_incompat);
+	super->s_feature_ro_compat = be64_to_cpu(ds->ds_feature_ro_compat);
+	super->s_feature_compat = be64_to_cpu(ds->ds_feature_compat);
+	super->s_feature_flags = be64_to_cpu(ds->ds_feature_flags);
+
+	journal_for_each(i)
+		super->s_journal_seg[i] = be32_to_cpu(ds->ds_journal_seg[i]);
+
+	super->s_ifile_levels = ds->ds_ifile_levels;
+	super->s_iblock_levels = ds->ds_iblock_levels;
+	super->s_data_levels = ds->ds_data_levels;
+	super->s_total_levels = super->s_ifile_levels + super->s_iblock_levels
+		+ super->s_data_levels;
+	page_cache_release(page);
+	return 0;
+}
+
+static int logfs_read_sb(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+	int ret;
+
+	super->s_btree_pool = mempool_create(32, btree_alloc, btree_free, NULL);
+	if (!super->s_btree_pool)
+		return -ENOMEM;
+
+	btree_init_mempool64(&super->s_shadow_tree.new, super->s_btree_pool);
+	btree_init_mempool64(&super->s_shadow_tree.old, super->s_btree_pool);
+
+	ret = logfs_init_mapping(sb);
+	if (ret)
+		return ret;
+
+	ret = __logfs_read_sb(sb);
+	if (ret)
+		return ret;
+
+	mutex_init(&super->s_dirop_mutex);
+	mutex_init(&super->s_object_alias_mutex);
+	INIT_LIST_HEAD(&super->s_freeing_list);
+
+	ret = logfs_init_rw(sb);
+	if (ret)
+		return ret;
+
+	ret = logfs_init_areas(sb);
+	if (ret)
+		return ret;
+
+	ret = logfs_init_gc(sb);
+	if (ret)
+		return ret;
+
+	ret = logfs_init_journal(sb);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static void logfs_kill_sb(struct super_block *sb)
+{
+	struct logfs_super *super = logfs_super(sb);
+
+	log_super("LogFS: Start unmounting\n");
+	/* Alias entries slow down mount, so evict as many as possible */
+	sync_filesystem(sb);
+	logfs_write_anchor(super->s_master_inode);
+
+	/*
+	 * From this point on alias entries are simply dropped - and any
+	 * writes to the object store are considered bugs.
+	 */
+	super->s_flags |= LOGFS_SB_FLAG_SHUTDOWN;
+	log_super("LogFS: Now in shutdown\n");
+	generic_shutdown_super(sb);
+
+	BUG_ON(super->s_dirty_used_bytes || super->s_dirty_free_bytes);
+
+	logfs_cleanup_gc(sb);
+	logfs_cleanup_journal(sb);
+	logfs_cleanup_areas(sb);
+	logfs_cleanup_rw(sb);
+	super->s_devops->put_device(sb);
+	mempool_destroy(super->s_btree_pool);
+	mempool_destroy(super->s_alias_pool);
+	kfree(super);
+	log_super("LogFS: Finished unmounting\n");
+}
+
+int logfs_get_sb_device(struct file_system_type *type, int flags,
+		struct mtd_info *mtd, struct block_device *bdev,
+		const struct logfs_device_ops *devops, struct vfsmount *mnt)
+{
+	struct logfs_super *super;
+	struct super_block *sb;
+	int err = -ENOMEM;
+	static int mount_count;
+
+	log_super("LogFS: Start mount %x\n", mount_count++);
+	super = kzalloc(sizeof(*super), GFP_KERNEL);
+	if (!super)
+		goto err0;
+
+	super->s_mtd	= mtd;
+	super->s_bdev	= bdev;
+	err = -EINVAL;
+	sb = sget(type, logfs_sb_test, logfs_sb_set, super);
+	if (IS_ERR(sb))
+		goto err0;
+
+	if (sb->s_root) {
+		/* Device is already in use */
+		err = 0;
+		simple_set_mnt(mnt, sb);
+		goto err0;
+	}
+
+	super->s_devops = devops;
+
+	/*
+	 * sb->s_maxbytes is limited to 8TB.  On 32bit systems, the page cache
+	 * only covers 16TB and the upper 8TB are used for indirect blocks.
+	 * On 64bit system we could bump up the limit, but that would make
+	 * the filesystem incompatible with 32bit systems.
+	 */
+	sb->s_maxbytes	= (1ull << 43) - 1;
+	sb->s_op	= &logfs_super_operations;
+	sb->s_flags	= flags | MS_NOATIME;
+
+	err = logfs_read_sb(sb);
+	if (err)
+		goto err1;
+
+	sb->s_flags |= MS_ACTIVE;
+	err = logfs_get_sb_final(sb, mnt);
+	if (err)
+		goto err1;
+	return 0;
+
+err1:
+	up_write(&sb->s_umount);
+	deactivate_super(sb);
+	return err;
+err0:
+	kfree(super);
+	//devops->put_device(sb);
+	return err;
+}
+
+static int logfs_get_sb(struct file_system_type *type, int flags,
+		const char *devname, void *data, struct vfsmount *mnt)
+{
+	ulong mtdnr;
+
+	if (!devname)
+		return logfs_get_sb_bdev(type, flags, devname, mnt);
+	if (strncmp(devname, "mtd", 3))
+		return logfs_get_sb_bdev(type, flags, devname, mnt);
+
+	{
+		char *garbage;
+		mtdnr = simple_strtoul(devname+3, &garbage, 0);
+		if (*garbage)
+			return -EINVAL;
+	}
+
+	return logfs_get_sb_mtd(type, flags, mtdnr, mnt);
+}
+
+static struct file_system_type logfs_fs_type = {
+	.owner		= THIS_MODULE,
+	.name		= "logfs",
+	.get_sb		= logfs_get_sb,
+	.kill_sb	= logfs_kill_sb,
+	.fs_flags	= FS_REQUIRES_DEV,
+
+};
+
+static int __init logfs_init(void)
+{
+	int ret;
+
+	emergency_page = alloc_pages(GFP_KERNEL, 0);
+	if (!emergency_page)
+		return -ENOMEM;
+
+	ret = logfs_compr_init();
+	if (ret)
+		goto out1;
+
+	ret = logfs_init_inode_cache();
+	if (ret)
+		goto out2;
+
+	return register_filesystem(&logfs_fs_type);
+out2:
+	logfs_compr_exit();
+out1:
+	__free_pages(emergency_page, 0);
+	return ret;
+}
+
+static void __exit logfs_exit(void)
+{
+	unregister_filesystem(&logfs_fs_type);
+	logfs_destroy_inode_cache();
+	logfs_compr_exit();
+	__free_pages(emergency_page, 0);
+}
+
+module_init(logfs_init);
+module_exit(logfs_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Joern Engel <[e-mail]>");
+MODULE_DESCRIPTION("scalable flash filesystem");

include/linux/btree-128.h

···
+extern struct btree_geo btree_geo128;
+
+struct btree_head128 { struct btree_head h; };
+
+static inline void btree_init_mempool128(struct btree_head128 *head,
+					 mempool_t *mempool)
+{
+	btree_init_mempool(&head->h, mempool);
+}
+
+static inline int btree_init128(struct btree_head128 *head)
+{
+	return btree_init(&head->h);
+}
+
+static inline void btree_destroy128(struct btree_head128 *head)
+{
+	btree_destroy(&head->h);
+}
+
+static inline void *btree_lookup128(struct btree_head128 *head, u64 k1, u64 k2)
+{
+	u64 key[2] = {k1, k2};
+	return btree_lookup(&head->h, &btree_geo128, (unsigned long *)&key);
+}
+
+static inline void *btree_get_prev128(struct btree_head128 *head,
+				      u64 *k1, u64 *k2)
+{
+	u64 key[2] = {*k1, *k2};
+	void *val;
+
+	val = btree_get_prev(&head->h, &btree_geo128,
+			     (unsigned long *)&key);
+	*k1 = key[0];
+	*k2 = key[1];
+	return val;
+}
+
+static inline int btree_insert128(struct btree_head128 *head, u64 k1, u64 k2,
+				  void *val, gfp_t gfp)
+{
+	u64 key[2] = {k1, k2};
+	return btree_insert(&head->h, &btree_geo128,
+			    (unsigned long *)&key, val, gfp);
+}
+
+static inline int btree_update128(struct btree_head128 *head, u64 k1, u64 k2,
+				  void *val)
+{
+	u64 key[2] = {k1, k2};
+	return btree_update(&head->h, &btree_geo128,
+			    (unsigned long *)&key, val);
+}
+
+static inline void *btree_remove128(struct btree_head128 *head, u64 k1, u64 k2)
+{
+	u64 key[2] = {k1, k2};
+	return btree_remove(&head->h, &btree_geo128, (unsigned long *)&key);
+}
+
+static inline void *btree_last128(struct btree_head128 *head, u64 *k1, u64 *k2)
+{
+	u64 key[2];
+	void *val;
+
+	val = btree_last(&head->h, &btree_geo128, (unsigned long *)&key[0]);
+	if (val) {
+		*k1 = key[0];
+		*k2 = key[1];
+	}
+
+	return val;
+}
+
+static inline int btree_merge128(struct btree_head128 *target,
+				 struct btree_head128 *victim,
+				 gfp_t gfp)
+{
+	return btree_merge(&target->h, &victim->h, &btree_geo128, gfp);
+}
+
+void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
+		size_t index, void *__func);
+
+typedef void (*visitor128_t)(void *elem, unsigned long opaque,
+			     u64 key1, u64 key2, size_t index);
+
+static inline size_t btree_visitor128(struct btree_head128 *head,
+				      unsigned long opaque,
+				      visitor128_t func2)
+{
+	return btree_visitor(&head->h, &btree_geo128, opaque,
+			     visitor128, func2);
+}
+
+static inline size_t btree_grim_visitor128(struct btree_head128 *head,
+					   unsigned long opaque,
+					   visitor128_t func2)
+{
+	return btree_grim_visitor(&head->h, &btree_geo128, opaque,
+				  visitor128, func2);
+}
+
+#define btree_for_each_safe128(head, k1, k2, val)	\
+	for (val = btree_last128(head, &k1, &k2);	\
+	     val;					\
+	     val = btree_get_prev128(head, &k1, &k2))
+

include/linux/btree-type.h

···
+#define __BTREE_TP(pfx, type, sfx)	pfx ## type ## sfx
+#define _BTREE_TP(pfx, type, sfx)	__BTREE_TP(pfx, type, sfx)
+#define BTREE_TP(pfx)			_BTREE_TP(pfx, BTREE_TYPE_SUFFIX,)
+#define BTREE_FN(name)			BTREE_TP(btree_ ## name)
+#define BTREE_TYPE_HEAD			BTREE_TP(struct btree_head)
+#define VISITOR_FN			BTREE_TP(visitor)
+#define VISITOR_FN_T			_BTREE_TP(visitor, BTREE_TYPE_SUFFIX, _t)
+
+BTREE_TYPE_HEAD {
+	struct btree_head h;
+};
+
+static inline void BTREE_FN(init_mempool)(BTREE_TYPE_HEAD *head,
+					  mempool_t *mempool)
+{
+	btree_init_mempool(&head->h, mempool);
+}
+
+static inline int BTREE_FN(init)(BTREE_TYPE_HEAD *head)
+{
+	return btree_init(&head->h);
+}
+
+static inline void BTREE_FN(destroy)(BTREE_TYPE_HEAD *head)
+{
+	btree_destroy(&head->h);
+}
+
+static inline int BTREE_FN(merge)(BTREE_TYPE_HEAD *target,
+				  BTREE_TYPE_HEAD *victim,
+				  gfp_t gfp)
+{
+	return btree_merge(&target->h, &victim->h, BTREE_TYPE_GEO, gfp);
+}
+
+#if (BITS_PER_LONG > BTREE_TYPE_BITS)
+static inline void *BTREE_FN(lookup)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key)
+{
+	unsigned long _key = key;
+	return btree_lookup(&head->h, BTREE_TYPE_GEO, &_key);
+}
+
+static inline int BTREE_FN(insert)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key,
+				   void *val, gfp_t gfp)
+{
+	unsigned long _key = key;
+	return btree_insert(&head->h, BTREE_TYPE_GEO, &_key, val, gfp);
+}
+
+static inline int BTREE_FN(update)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key,
+		void *val)
+{
+	unsigned long _key = key;
+	return btree_update(&head->h, BTREE_TYPE_GEO, &_key, val);
+}
+
+static inline void *BTREE_FN(remove)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key)
+{
+	unsigned long _key = key;
+	return btree_remove(&head->h, BTREE_TYPE_GEO, &_key);
+}
+
+static inline void *BTREE_FN(last)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE *key)
+{
+	unsigned long _key;
+	void *val = btree_last(&head->h, BTREE_TYPE_GEO, &_key);
+	if (val)
+		*key = _key;
+	return val;
+}
+
+static inline void *BTREE_FN(get_prev)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE *key)
+{
+	unsigned long _key = *key;
+	void *val = btree_get_prev(&head->h, BTREE_TYPE_GEO, &_key);
+	if (val)
+		*key = _key;
+	return val;
+}
+#else
+static inline void *BTREE_FN(lookup)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key)
+{
+	return btree_lookup(&head->h, BTREE_TYPE_GEO, (unsigned long *)&key);
+}
+
+static inline int BTREE_FN(insert)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key,
+			   void *val, gfp_t gfp)
+{
+	return btree_insert(&head->h, BTREE_TYPE_GEO, (unsigned long *)&key,
+			    val, gfp);
+}
+
+static inline int BTREE_FN(update)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key,
+		void *val)
+{
+	return btree_update(&head->h, BTREE_TYPE_GEO, (unsigned long *)&key, val);
+}
+
+static inline void *BTREE_FN(remove)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE key)
+{
+	return btree_remove(&head->h, BTREE_TYPE_GEO, (unsigned long *)&key);
+}
+
+static inline void *BTREE_FN(last)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE *key)
+{
+	return btree_last(&head->h, BTREE_TYPE_GEO, (unsigned long *)key);
+}
+
+static inline void *BTREE_FN(get_prev)(BTREE_TYPE_HEAD *head, BTREE_KEYTYPE *key)
+{
+	return btree_get_prev(&head->h, BTREE_TYPE_GEO, (unsigned long *)key);
+}
+#endif
+
+void VISITOR_FN(void *elem, unsigned long opaque, unsigned long *key,
+		size_t index, void *__func);
+
+typedef void (*VISITOR_FN_T)(void *elem, unsigned long opaque,
+			     BTREE_KEYTYPE key, size_t index);
+
+static inline size_t BTREE_FN(visitor)(BTREE_TYPE_HEAD *head,
+				       unsigned long opaque,
+				       VISITOR_FN_T func2)
+{
+	return btree_visitor(&head->h, BTREE_TYPE_GEO, opaque,
+			     visitorl, func2);
+}
+
+static inline size_t BTREE_FN(grim_visitor)(BTREE_TYPE_HEAD *head,
+					    unsigned long opaque,
+					    VISITOR_FN_T func2)
+{
+	return btree_grim_visitor(&head->h, BTREE_TYPE_GEO, opaque,
+				  visitorl, func2);
+}
+
+#undef VISITOR_FN
+#undef VISITOR_FN_T
+#undef __BTREE_TP
+#undef _BTREE_TP
+#undef BTREE_TP
+#undef BTREE_FN
+#undef BTREE_TYPE_HEAD
+#undef BTREE_TYPE_SUFFIX
+#undef BTREE_TYPE_GEO
+#undef BTREE_KEYTYPE
+#undef BTREE_TYPE_BITS

include/linux/btree.h

···
+#ifndef BTREE_H
+#define BTREE_H
+
+#include <linux/kernel.h>
+#include <linux/mempool.h>
+
+/**
+ * DOC: B+Tree basics
+ *
+ * A B+Tree is a data structure for looking up arbitrary (currently allowing
+ * unsigned long, u32, u64 and 2 * u64) keys into pointers. The data structure
+ * is described at http://en.wikipedia.org/wiki/B-tree, we currently do not
+ * use binary search to find the key on lookups.
+ *
+ * Each B+Tree consists of a head, that contains bookkeeping information and
+ * a variable number (starting with zero) nodes. Each node contains the keys
+ * and pointers to sub-nodes, or, for leaf nodes, the keys and values for the
+ * tree entries.
+ *
+ * Each node in this implementation has the following layout:
+ * [key1, key2, ..., keyN] [val1, val2, ..., valN]
+ *
+ * Each key here is an array of unsigned longs, geo->no_longs in total. The
+ * number of keys and values (N) is geo->no_pairs.
+ */
+
+/**
+ * struct btree_head - btree head
+ *
+ * @node: the first node in the tree
+ * @mempool: mempool used for node allocations
+ * @height: current of the tree
+ */
+struct btree_head {
+	unsigned long *node;
+	mempool_t *mempool;
+	int height;
+};
+
+/* btree geometry */
+struct btree_geo;
+
+/**
+ * btree_alloc - allocate function for the mempool
+ * @gfp_mask: gfp mask for the allocation
+ * @pool_data: unused
+ */
+void *btree_alloc(gfp_t gfp_mask, void *pool_data);
+
+/**
+ * btree_free - free function for the mempool
+ * @element: the element to free
+ * @pool_data: unused
+ */
+void btree_free(void *element, void *pool_data);
+
+/**
+ * btree_init_mempool - initialise a btree with given mempool
+ *
+ * @head: the btree head to initialise
+ * @mempool: the mempool to use
+ *
+ * When this function is used, there is no need to destroy
+ * the mempool.
+ */
+void btree_init_mempool(struct btree_head *head, mempool_t *mempool);
+
+/**
+ * btree_init - initialise a btree
+ *
+ * @head: the btree head to initialise
+ *
+ * This function allocates the memory pool that the
+ * btree needs. Returns zero or a negative error code
+ * (-%ENOMEM) when memory allocation fails.
+ *
+ */
+int __must_check btree_init(struct btree_head *head);
+
+/**
+ * btree_destroy - destroy mempool
+ *
+ * @head: the btree head to destroy
+ *
+ * This function destroys the internal memory pool, use only
+ * when using btree_init(), not with btree_init_mempool().
+ */
+void btree_destroy(struct btree_head *head);
+
+/**
+ * btree_lookup - look up a key in the btree
+ *
+ * @head: the btree to look in
+ * @geo: the btree geometry
+ * @key: the key to look up
+ *
+ * This function returns the value for the given key, or %NULL.
+ */
+void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
+		   unsigned long *key);
+
+/**
+ * btree_insert - insert an entry into the btree
+ *
+ * @head: the btree to add to
+ * @geo: the btree geometry
+ * @key: the key to add (must not already be present)
+ * @val: the value to add (must not be %NULL)
+ * @gfp: allocation flags for node allocations
+ *
+ * This function returns 0 if the item could be added, or an
+ * error code if it failed (may fail due to memory pressure).
+ */
+int __must_check btree_insert(struct btree_head *head, struct btree_geo *geo,
+			      unsigned long *key, void *val, gfp_t gfp);
+/**
+ * btree_update - update an entry in the btree
+ *
+ * @head: the btree to update
+ * @geo: the btree geometry
+ * @key: the key to update
+ * @val: the value to change it to (must not be %NULL)
+ *
+ * This function returns 0 if the update was successful, or
+ * -%ENOENT if the key could not be found.
+ */
+int btree_update(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key, void *val);
+/**
+ * btree_remove - remove an entry from the btree
+ *
+ * @head: the btree to update
+ * @geo: the btree geometry
+ * @key: the key to remove
+ *
+ * This function returns the removed entry, or %NULL if the key
+ * could not be found.
+ */
+void *btree_remove(struct btree_head *head, struct btree_geo *geo,
+		   unsigned long *key);
+
+/**
+ * btree_merge - merge two btrees
+ *
+ * @target: the tree that gets all the entries
+ * @victim: the tree that gets merged into @target
+ * @geo: the btree geometry
+ * @gfp: allocation flags
+ *
+ * The two trees @target and @victim may not contain the same keys,
+ * that is a bug and triggers a BUG(). This function returns zero
+ * if the trees were merged successfully, and may return a failure
+ * when memory allocation fails, in which case both trees might have
+ * been partially merged, i.e. some entries have been moved from
+ * @victim to @target.
+ */
+int btree_merge(struct btree_head *target, struct btree_head *victim,
+		struct btree_geo *geo, gfp_t gfp);
+
+/**
+ * btree_last - get last entry in btree
+ *
+ * @head: btree head
+ * @geo: btree geometry
+ * @key: last key
+ *
+ * Returns the last entry in the btree, and sets @key to the key
+ * of that entry; returns NULL if the tree is empty, in that case
+ * key is not changed.
+ */
+void *btree_last(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key);
+
+/**
+ * btree_get_prev - get previous entry
+ *
+ * @head: btree head
+ * @geo: btree geometry
+ * @key: pointer to key
+ *
+ * The function returns the next item right before the value pointed to by
+ * @key, and updates @key with its key, or returns %NULL when there is no
+ * entry with a key smaller than the given key.
+ */
+void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long *key);
+
+
+/* internal use, use btree_visitor{l,32,64,128} */
+size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long opaque,
+		     void (*func)(void *elem, unsigned long opaque,
+				  unsigned long *key, size_t index,
+				  void *func2),
+		     void *func2);
+
+/* internal use, use btree_grim_visitor{l,32,64,128} */
+size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
+			  unsigned long opaque,
+			  void (*func)(void *elem, unsigned long opaque,
+				       unsigned long *key,
+				       size_t index, void *func2),
+			  void *func2);
+
+
+#include <linux/btree-128.h>
+
+extern struct btree_geo btree_geo32;
+#define BTREE_TYPE_SUFFIX l
+#define BTREE_TYPE_BITS BITS_PER_LONG
+#define BTREE_TYPE_GEO &btree_geo32
+#define BTREE_KEYTYPE unsigned long
+#include <linux/btree-type.h>
+
+#define btree_for_each_safel(head, key, val)	\
+	for (val = btree_lastl(head, &key);	\
+	     val;				\
+	     val = btree_get_prevl(head, &key))
+
+#define BTREE_TYPE_SUFFIX 32
+#define BTREE_TYPE_BITS 32
+#define BTREE_TYPE_GEO &btree_geo32
+#define BTREE_KEYTYPE u32
+#include <linux/btree-type.h>
+
+#define btree_for_each_safe32(head, key, val)	\
+	for (val = btree_last32(head, &key);	\
+	     val;				\
+	     val = btree_get_prev32(head, &key))
+
+extern struct btree_geo btree_geo64;
+#define BTREE_TYPE_SUFFIX 64
+#define BTREE_TYPE_BITS 64
+#define BTREE_TYPE_GEO &btree_geo64
+#define BTREE_KEYTYPE u64
+#include <linux/btree-type.h>
+
+#define btree_for_each_safe64(head, key, val)	\
+	for (val = btree_last64(head, &key);	\
+	     val;				\
+	     val = btree_get_prev64(head, &key))
+
+#endif

lib/Kconfig

···
 config TEXTSEARCH_FSM
 	tristate
 
+config BTREE
+	boolean
+
 config HAS_IOMEM
 	boolean
 	depends on !NO_IOMEM

lib/Makefile

···
 obj-$(CONFIG_GENERIC_FIND_LAST_BIT) += find_last_bit.o
 obj-$(CONFIG_GENERIC_HWEIGHT) += hweight.o
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
+obj-$(CONFIG_BTREE) += btree.o
 obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
 obj-$(CONFIG_DEBUG_LIST) += list_debug.o
 obj-$(CONFIG_DEBUG_OBJECTS) += debugobjects.o

lib/btree.c

···
+/*
+ * lib/btree.c	- Simple In-memory B+Tree
+ *
+ * As should be obvious for Linux kernel code, license is GPLv2
+ *
+ * Copyright (c) 2007-2008 Joern Engel <[e-mail]>
+ * Bits and pieces stolen from Peter Zijlstra's code, which is
+ * Copyright 2007, Red Hat Inc. Peter Zijlstra <[e-mail]>
+ * GPLv2
+ *
+ * see http://programming.kicks-ass.net/kernel-patches/vma_lookup/btree.patch
+ *
+ * A relatively simple B+Tree implementation.  I have written it as a learning
+ * excercise to understand how B+Trees work.  Turned out to be useful as well.
+ *
+ * B+Trees can be used similar to Linux radix trees (which don't have anything
+ * in common with textbook radix trees, beware).  Prerequisite for them working
+ * well is that access to a random tree node is much faster than a large number
+ * of operations within each node.
+ *
+ * Disks have fulfilled the prerequisite for a long time.  More recently DRAM
+ * has gained similar properties, as memory access times, when measured in cpu
+ * cycles, have increased.  Cacheline sizes have increased as well, which also
+ * helps B+Trees.
+ *
+ * Compared to radix trees, B+Trees are more efficient when dealing with a
+ * sparsely populated address space.  Between 25% and 50% of the memory is
+ * occupied with valid pointers.  When densely populated, radix trees contain
+ * ~98% pointers - hard to beat.  Very sparse radix trees contain only ~2%
+ * pointers.
+ *
+ * This particular implementation stores pointers identified by a long value.
+ * Storing NULL pointers is illegal, lookup will return NULL when no entry
+ * was found.
+ *
+ * A tricks was used that is not commonly found in textbooks.  The lowest
+ * values are to the right, not to the left.  All used slots within a node
+ * are on the left, all unused slots contain NUL values.  Most operations
+ * simply loop once over all slots and terminate on the first NUL.
+ */
+
+#include <linux/btree.h>
+#include <linux/cache.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#define NODESIZE MAX(L1_CACHE_BYTES, 128)
+
+struct btree_geo {
+	int keylen;
+	int no_pairs;
+	int no_longs;
+};
+
+struct btree_geo btree_geo32 = {
+	.keylen = 1,
+	.no_pairs = NODESIZE / sizeof(long) / 2,
+	.no_longs = NODESIZE / sizeof(long) / 2,
+};
+EXPORT_SYMBOL_GPL(btree_geo32);
+
+#define LONG_PER_U64 (64 / BITS_PER_LONG)
+struct btree_geo btree_geo64 = {
+	.keylen = LONG_PER_U64,
+	.no_pairs = NODESIZE / sizeof(long) / (1 + LONG_PER_U64),
+	.no_longs = LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo64);
+
+struct btree_geo btree_geo128 = {
+	.keylen = 2 * LONG_PER_U64,
+	.no_pairs = NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64),
+	.no_longs = 2 * LONG_PER_U64 * (NODESIZE / sizeof(long) / (1 + 2 * LONG_PER_U64)),
+};
+EXPORT_SYMBOL_GPL(btree_geo128);
+
+static struct kmem_cache *btree_cachep;
+
+void *btree_alloc(gfp_t gfp_mask, void *pool_data)
+{
+	return kmem_cache_alloc(btree_cachep, gfp_mask);
+}
+EXPORT_SYMBOL_GPL(btree_alloc);
+
+void btree_free(void *element, void *pool_data)
+{
+	kmem_cache_free(btree_cachep, element);
+}
+EXPORT_SYMBOL_GPL(btree_free);
+
+static unsigned long *btree_node_alloc(struct btree_head *head, gfp_t gfp)
+{
+	unsigned long *node;
+
+	node = mempool_alloc(head->mempool, gfp);
+	memset(node, 0, NODESIZE);
+	return node;
+}
+
+static int longcmp(const unsigned long *l1, const unsigned long *l2, size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++) {
+		if (l1[i] < l2[i])
+			return -1;
+		if (l1[i] > l2[i])
+			return 1;
+	}
+	return 0;
+}
+
+static unsigned long *longcpy(unsigned long *dest, const unsigned long *src,
+		size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		dest[i] = src[i];
+	return dest;
+}
+
+static unsigned long *longset(unsigned long *s, unsigned long c, size_t n)
+{
+	size_t i;
+
+	for (i = 0; i < n; i++)
+		s[i] = c;
+	return s;
+}
+
+static void dec_key(struct btree_geo *geo, unsigned long *key)
+{
+	unsigned long val;
+	int i;
+
+	for (i = geo->keylen - 1; i >= 0; i--) {
+		val = key[i];
+		key[i] = val - 1;
+		if (val)
+			break;
+	}
+}
+
+static unsigned long *bkey(struct btree_geo *geo, unsigned long *node, int n)
+{
+	return &node[n * geo->keylen];
+}
+
+static void *bval(struct btree_geo *geo, unsigned long *node, int n)
+{
+	return (void *)node[geo->no_longs + n];
+}
+
+static void setkey(struct btree_geo *geo, unsigned long *node, int n,
+		   unsigned long *key)
+{
+	longcpy(bkey(geo, node, n), key, geo->keylen);
+}
+
+static void setval(struct btree_geo *geo, unsigned long *node, int n,
+		   void *val)
+{
+	node[geo->no_longs + n] = (unsigned long) val;
+}
+
+static void clearpair(struct btree_geo *geo, unsigned long *node, int n)
+{
+	longset(bkey(geo, node, n), 0, geo->keylen);
+	node[geo->no_longs + n] = 0;
+}
+
+static inline void __btree_init(struct btree_head *head)
+{
+	head->node = NULL;
+	head->height = 0;
+}
+
+void btree_init_mempool(struct btree_head *head, mempool_t *mempool)
+{
+	__btree_init(head);
+	head->mempool = mempool;
+}
+EXPORT_SYMBOL_GPL(btree_init_mempool);
+
+int btree_init(struct btree_head *head)
+{
+	__btree_init(head);
+	head->mempool = mempool_create(0, btree_alloc, btree_free, NULL);
+	if (!head->mempool)
+		return -ENOMEM;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btree_init);
+
+void btree_destroy(struct btree_head *head)
+{
+	mempool_destroy(head->mempool);
+	head->mempool = NULL;
+}
+EXPORT_SYMBOL_GPL(btree_destroy);
+
+void *btree_last(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key)
+{
+	int height = head->height;
+	unsigned long *node = head->node;
+
+	if (height == 0)
+		return NULL;
+
+	for ( ; height > 1; height--)
+		node = bval(geo, node, 0);
+
+	longcpy(key, bkey(geo, node, 0), geo->keylen);
+	return bval(geo, node, 0);
+}
+EXPORT_SYMBOL_GPL(btree_last);
+
+static int keycmp(struct btree_geo *geo, unsigned long *node, int pos,
+		  unsigned long *key)
+{
+	return longcmp(bkey(geo, node, pos), key, geo->keylen);
+}
+
+static int keyzero(struct btree_geo *geo, unsigned long *key)
+{
+	int i;
+
+	for (i = 0; i < geo->keylen; i++)
+		if (key[i])
+			return 0;
+
+	return 1;
+}
+
+void *btree_lookup(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key)
+{
+	int i, height = head->height;
+	unsigned long *node = head->node;
+
+	if (height == 0)
+		return NULL;
+
+	for ( ; height > 1; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+		if (i == geo->no_pairs)
+			return NULL;
+		node = bval(geo, node, i);
+		if (!node)
+			return NULL;
+	}
+
+	if (!node)
+		return NULL;
+
+	for (i = 0; i < geo->no_pairs; i++)
+		if (keycmp(geo, node, i, key) == 0)
+			return bval(geo, node, i);
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(btree_lookup);
+
+int btree_update(struct btree_head *head, struct btree_geo *geo,
+		 unsigned long *key, void *val)
+{
+	int i, height = head->height;
+	unsigned long *node = head->node;
+
+	if (height == 0)
+		return -ENOENT;
+
+	for ( ; height > 1; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+		if (i == geo->no_pairs)
+			return -ENOENT;
+		node = bval(geo, node, i);
+		if (!node)
+			return -ENOENT;
+	}
+
+	if (!node)
+		return -ENOENT;
+
+	for (i = 0; i < geo->no_pairs; i++)
+		if (keycmp(geo, node, i, key) == 0) {
+			setval(geo, node, i, val);
+			return 0;
+		}
+	return -ENOENT;
+}
+EXPORT_SYMBOL_GPL(btree_update);
+
+/*
+ * Usually this function is quite similar to normal lookup.  But the key of
+ * a parent node may be smaller than the smallest key of all its siblings.
+ * In such a case we cannot just return NULL, as we have only proven that no
+ * key smaller than __key, but larger than this parent key exists.
+ * So we set __key to the parent key and retry.  We have to use the smallest
+ * such parent key, which is the last parent key we encountered.
+ */
+void *btree_get_prev(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long *__key)
+{
+	int i, height;
+	unsigned long *node, *oldnode;
+	unsigned long *retry_key = NULL, key[geo->keylen];
+
+	if (keyzero(geo, __key))
+		return NULL;
+
+	if (head->height == 0)
+		return NULL;
+retry:
+	longcpy(key, __key, geo->keylen);
+	dec_key(geo, key);
+
+	node = head->node;
+	for (height = head->height ; height > 1; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+		if (i == geo->no_pairs)
+			goto miss;
+		oldnode = node;
+		node = bval(geo, node, i);
+		if (!node)
+			goto miss;
+		retry_key = bkey(geo, oldnode, i);
+	}
+
+	if (!node)
+		goto miss;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		if (keycmp(geo, node, i, key) <= 0) {
+			if (bval(geo, node, i)) {
+				longcpy(__key, bkey(geo, node, i), geo->keylen);
+				return bval(geo, node, i);
+			} else
+				goto miss;
+		}
+	}
+miss:
+	if (retry_key) {
+		__key = retry_key;
+		retry_key = NULL;
+		goto retry;
+	}
+	return NULL;
+}
+
+static int getpos(struct btree_geo *geo, unsigned long *node,
+		unsigned long *key)
+{
+	int i;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		if (keycmp(geo, node, i, key) <= 0)
+			break;
+	}
+	return i;
+}
+
+static int getfill(struct btree_geo *geo, unsigned long *node, int start)
+{
+	int i;
+
+	for (i = start; i < geo->no_pairs; i++)
+		if (!bval(geo, node, i))
+			break;
+	return i;
+}
+
+/*
+ * locate the correct leaf node in the btree
+ */
+static unsigned long *find_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level)
+{
+	unsigned long *node = head->node;
+	int i, height;
+
+	for (height = head->height; height > level; height--) {
+		for (i = 0; i < geo->no_pairs; i++)
+			if (keycmp(geo, node, i, key) <= 0)
+				break;
+
+		if ((i == geo->no_pairs) || !bval(geo, node, i)) {
+			/* right-most key is too large, update it */
+			/* FIXME: If the right-most key on higher levels is
+			 * always zero, this wouldn't be necessary. */
+			i--;
+			setkey(geo, node, i, key);
+		}
+		BUG_ON(i < 0);
+		node = bval(geo, node, i);
+	}
+	BUG_ON(!node);
+	return node;
+}
+
+static int btree_grow(struct btree_head *head, struct btree_geo *geo,
+		      gfp_t gfp)
+{
+	unsigned long *node;
+	int fill;
+
+	node = btree_node_alloc(head, gfp);
+	if (!node)
+		return -ENOMEM;
+	if (head->node) {
+		fill = getfill(geo, head->node, 0);
+		setkey(geo, node, 0, bkey(geo, head->node, fill - 1));
+		setval(geo, node, 0, head->node);
+	}
+	head->node = node;
+	head->height++;
+	return 0;
+}
+
+static void btree_shrink(struct btree_head *head, struct btree_geo *geo)
+{
+	unsigned long *node;
+	int fill;
+
+	if (head->height <= 1)
+		return;
+
+	node = head->node;
+	fill = getfill(geo, node, 0);
+	BUG_ON(fill > 1);
+	head->node = bval(geo, node, 0);
+	head->height--;
+	mempool_free(node, head->mempool);
+}
+
+static int btree_insert_level(struct btree_head *head, struct btree_geo *geo,
+			      unsigned long *key, void *val, int level,
+			      gfp_t gfp)
+{
+	unsigned long *node;
+	int i, pos, fill, err;
+
+	BUG_ON(!val);
+	if (head->height < level) {
+		err = btree_grow(head, geo, gfp);
+		if (err)
+			return err;
+	}
+
+retry:
+	node = find_level(head, geo, key, level);
+	pos = getpos(geo, node, key);
+	fill = getfill(geo, node, pos);
+	/* two identical keys are not allowed */
+	BUG_ON(pos < fill && keycmp(geo, node, pos, key) == 0);
+
+	if (fill == geo->no_pairs) {
+		/* need to split node */
+		unsigned long *new;
+
+		new = btree_node_alloc(head, gfp);
+		if (!new)
+			return -ENOMEM;
+		err = btree_insert_level(head, geo,
+				bkey(geo, node, fill / 2 - 1),
+				new, level + 1, gfp);
+		if (err) {
+			mempool_free(new, head->mempool);
+			return err;
+		}
+		for (i = 0; i < fill / 2; i++) {
+			setkey(geo, new, i, bkey(geo, node, i));
+			setval(geo, new, i, bval(geo, node, i));
+			setkey(geo, node, i, bkey(geo, node, i + fill / 2));
+			setval(geo, node, i, bval(geo, node, i + fill / 2));
+			clearpair(geo, node, i + fill / 2);
+		}
+		if (fill & 1) {
+			setkey(geo, node, i, bkey(geo, node, fill - 1));
+			setval(geo, node, i, bval(geo, node, fill - 1));
+			clearpair(geo, node, fill - 1);
+		}
+		goto retry;
+	}
+	BUG_ON(fill >= geo->no_pairs);
+
+	/* shift and insert */
+	for (i = fill; i > pos; i--) {
+		setkey(geo, node, i, bkey(geo, node, i - 1));
+		setval(geo, node, i, bval(geo, node, i - 1));
+	}
+	setkey(geo, node, pos, key);
+	setval(geo, node, pos, val);
+
+	return 0;
+}
+
+int btree_insert(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, void *val, gfp_t gfp)
+{
+	return btree_insert_level(head, geo, key, val, 1, gfp);
+}
+EXPORT_SYMBOL_GPL(btree_insert);
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level);
+static void merge(struct btree_head *head, struct btree_geo *geo, int level,
+		unsigned long *left, int lfill,
+		unsigned long *right, int rfill,
+		unsigned long *parent, int lpos)
+{
+	int i;
+
+	for (i = 0; i < rfill; i++) {
+		/* Move all keys to the left */
+		setkey(geo, left, lfill + i, bkey(geo, right, i));
+		setval(geo, left, lfill + i, bval(geo, right, i));
+	}
+	/* Exchange left and right child in parent */
+	setval(geo, parent, lpos, right);
+	setval(geo, parent, lpos + 1, left);
+	/* Remove left (formerly right) child from parent */
+	btree_remove_level(head, geo, bkey(geo, parent, lpos), level + 1);
+	mempool_free(right, head->mempool);
+}
+
+static void rebalance(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level, unsigned long *child, int fill)
+{
+	unsigned long *parent, *left = NULL, *right = NULL;
+	int i, no_left, no_right;
+
+	if (fill == 0) {
+		/* Because we don't steal entries from a neigbour, this case
+		 * can happen.  Parent node contains a single child, this
+		 * node, so merging with a sibling never happens.
+		 */
+		btree_remove_level(head, geo, key, level + 1);
+		mempool_free(child, head->mempool);
+		return;
+	}
+
+	parent = find_level(head, geo, key, level + 1);
+	i = getpos(geo, parent, key);
+	BUG_ON(bval(geo, parent, i) != child);
+
+	if (i > 0) {
+		left = bval(geo, parent, i - 1);
+		no_left = getfill(geo, left, 0);
+		if (fill + no_left <= geo->no_pairs) {
+			merge(head, geo, level,
+					left, no_left,
+					child, fill,
+					parent, i - 1);
+			return;
+		}
+	}
+	if (i + 1 < getfill(geo, parent, i)) {
+		right = bval(geo, parent, i + 1);
+		no_right = getfill(geo, right, 0);
+		if (fill + no_right <= geo->no_pairs) {
+			merge(head, geo, level,
+					child, fill,
+					right, no_right,
+					parent, i);
+			return;
+		}
+	}
+	/*
+	 * We could also try to steal one entry from the left or right
+	 * neighbor.  By not doing so we changed the invariant from
+	 * "all nodes are at least half full" to "no two neighboring
+	 * nodes can be merged".  Which means that the average fill of
+	 * all nodes is still half or better.
+	 */
+}
+
+static void *btree_remove_level(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key, int level)
+{
+	unsigned long *node;
+	int i, pos, fill;
+	void *ret;
+
+	if (level > head->height) {
+		/* we recursed all the way up */
+		head->height = 0;
+		head->node = NULL;
+		return NULL;
+	}
+
+	node = find_level(head, geo, key, level);
+	pos = getpos(geo, node, key);
+	fill = getfill(geo, node, pos);
+	if ((level == 1) && (keycmp(geo, node, pos, key) != 0))
+		return NULL;
+	ret = bval(geo, node, pos);
+
+	/* remove and shift */
+	for (i = pos; i < fill - 1; i++) {
+		setkey(geo, node, i, bkey(geo, node, i + 1));
+		setval(geo, node, i, bval(geo, node, i + 1));
+	}
+	clearpair(geo, node, fill - 1);
+
+	if (fill - 1 < geo->no_pairs / 2) {
+		if (level < head->height)
+			rebalance(head, geo, key, level, node, fill - 1);
+		else if (fill - 1 == 1)
+			btree_shrink(head, geo);
+	}
+
+	return ret;
+}
+
+void *btree_remove(struct btree_head *head, struct btree_geo *geo,
+		unsigned long *key)
+{
+	if (head->height == 0)
+		return NULL;
+
+	return btree_remove_level(head, geo, key, 1);
+}
+EXPORT_SYMBOL_GPL(btree_remove);
+
+int btree_merge(struct btree_head *target, struct btree_head *victim,
+		struct btree_geo *geo, gfp_t gfp)
+{
+	unsigned long key[geo->keylen];
+	unsigned long dup[geo->keylen];
+	void *val;
+	int err;
+
+	BUG_ON(target == victim);
+
+	if (!(target->node)) {
+		/* target is empty, just copy fields over */
+		target->node = victim->node;
+		target->height = victim->height;
+		__btree_init(victim);
+		return 0;
+	}
+
+	/* TODO: This needs some optimizations.  Currently we do three tree
+	 * walks to remove a single object from the victim.
+	 */
+	for (;;) {
+		if (!btree_last(victim, geo, key))
+			break;
+		val = btree_lookup(victim, geo, key);
+		err = btree_insert(target, geo, key, val, gfp);
+		if (err)
+			return err;
+		/* We must make a copy of the key, as the original will get
+		 * mangled inside btree_remove. */
+		longcpy(dup, key, geo->keylen);
+		btree_remove(victim, geo, dup);
+	}
+	return 0;
+}
+EXPORT_SYMBOL_GPL(btree_merge);
+
+static size_t __btree_for_each(struct btree_head *head, struct btree_geo *geo,
+			       unsigned long *node, unsigned long opaque,
+			       void (*func)(void *elem, unsigned long opaque,
+					    unsigned long *key, size_t index,
+					    void *func2),
+			       void *func2, int reap, int height, size_t count)
+{
+	int i;
+	unsigned long *child;
+
+	for (i = 0; i < geo->no_pairs; i++) {
+		child = bval(geo, node, i);
+		if (!child)
+			break;
+		if (height > 1)
+			count = __btree_for_each(head, geo, child, opaque,
+					func, func2, reap, height - 1, count);
+		else
+			func(child, opaque, bkey(geo, node, i), count++,
+					func2);
+	}
+	if (reap)
+		mempool_free(node, head->mempool);
+	return count;
+}
+
+static void empty(void *elem, unsigned long opaque, unsigned long *key,
+		  size_t index, void *func2)
+{
+}
+
+void visitorl(void *elem, unsigned long opaque, unsigned long *key,
+	      size_t index, void *__func)
+{
+	visitorl_t func = __func;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitorl);
+
+void visitor32(void *elem, unsigned long opaque, unsigned long *__key,
+	       size_t index, void *__func)
+{
+	visitor32_t func = __func;
+	u32 *key = (void *)__key;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor32);
+
+void visitor64(void *elem, unsigned long opaque, unsigned long *__key,
+	       size_t index, void *__func)
+{
+	visitor64_t func = __func;
+	u64 *key = (void *)__key;
+
+	func(elem, opaque, *key, index);
+}
+EXPORT_SYMBOL_GPL(visitor64);
+
+void visitor128(void *elem, unsigned long opaque, unsigned long *__key,
+		size_t index, void *__func)
+{
+	visitor128_t func = __func;
+	u64 *key = (void *)__key;
+
+	func(elem, opaque, key[0], key[1], index);
+}
+EXPORT_SYMBOL_GPL(visitor128);
+
+size_t btree_visitor(struct btree_head *head, struct btree_geo *geo,
+		     unsigned long opaque,
+		     void (*func)(void *elem, unsigned long opaque,
+		     		  unsigned long *key,
+		     		  size_t index, void *func2),
+		     void *func2)
+{
+	size_t count = 0;
+
+	if (!func2)
+		func = empty;
+	if (head->node)
+		count = __btree_for_each(head, geo, head->node, opaque, func,
+				func2, 0, head->height, 0);
+	return count;
+}
+EXPORT_SYMBOL_GPL(btree_visitor);
+
+size_t btree_grim_visitor(struct btree_head *head, struct btree_geo *geo,
+			  unsigned long opaque,
+			  void (*func)(void *elem, unsigned long opaque,
+				       unsigned long *key,
+				       size_t index, void *func2),
+			  void *func2)
+{
+	size_t count = 0;
+
+	if (!func2)
+		func = empty;
+	if (head->node)
+		count = __btree_for_each(head, geo, head->node, opaque, func,
+				func2, 1, head->height, 0);
+	__btree_init(head);
+	return count;
+}
+EXPORT_SYMBOL_GPL(btree_grim_visitor);
+
+static int __init btree_module_init(void)
+{
+	btree_cachep = kmem_cache_create("btree_node", NODESIZE, 0,
+			SLAB_HWCACHE_ALIGN, NULL);
+	return 0;
+}
+
+static void __exit btree_module_exit(void)
+{
+	kmem_cache_destroy(btree_cachep);
+}
+
+/* If core code starts using btree, initialization should happen even earlier */
+module_init(btree_module_init);
+module_exit(btree_module_exit);
+
+MODULE_AUTHOR("Joern Engel <[e-mail]>");
+MODULE_AUTHOR("Johannes Berg <[e-mail]>");
+MODULE_LICENSE("GPL");