dax: move DAX-related functions to a new header

In order to handle the !CONFIG_TRANSPARENT_HUGEPAGES case, we need to
return VM_FAULT_FALLBACK from the inlined dax_pmd_fault(), which is
defined in linux/mm.h. Given that we don't want to include <linux/mm.h>
in <linux/fs.h>, the easiest solution is to move the DAX-related
functions to a new header, <linux/dax.h>. We could also have moved
VM_FAULT_* definitions to a new header, or a different header that isn't
quite such a boil-the-ocean header as <linux/mm.h>, but this felt like
the best option.

Signed-off-by: Matthew Wilcox <[e-mail]>
Cc: Hillf Danton <[e-mail]>
Cc: "Kirill A. Shutemov" <[e-mail]>
Cc: Theodore Ts'o <[e-mail]>
Cc: Jan Kara <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/block_dev.c

···
 #include <linux/namei.h>
 #include <linux/log2.h>
 #include <linux/cleancache.h>
+#include <linux/dax.h>
 #include <asm/uaccess.h>
 #include "internal.h"
 

fs/ext2/file.c

···
 
 #include <linux/time.h>
 #include <linux/pagemap.h>
+#include <linux/dax.h>
 #include <linux/quotaops.h>
 #include "ext2.h"
 #include "xattr.h"

fs/ext2/inode.c

···
 #include <linux/time.h>
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
+#include <linux/dax.h>
 #include <linux/quotaops.h>
 #include <linux/writeback.h>
 #include <linux/buffer_head.h>

fs/ext4/file.c

···
 #include <linux/fs.h>
 #include <linux/mount.h>
 #include <linux/path.h>
+#include <linux/dax.h>
 #include <linux/quotaops.h>
 #include <linux/pagevec.h>
 #include <linux/uio.h>

fs/ext4/indirect.c

···
 
 #include "ext4_jbd2.h"
 #include "truncate.h"
+#include <linux/dax.h>
 #include <linux/uio.h>
 
 #include <trace/events/ext4.h>

fs/ext4/inode.c

···
 #include <linux/time.h>
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
+#include <linux/dax.h>
 #include <linux/quotaops.h>
 #include <linux/string.h>
 #include <linux/buffer_head.h>

fs/xfs/xfs_buf.h

···
 #include <linux/spinlock.h>
 #include <linux/mm.h>
 #include <linux/fs.h>
+#include <linux/dax.h>
 #include <linux/buffer_head.h>
 #include <linux/uio.h>
 #include <linux/list_lru.h>

include/linux/dax.h

···
+#ifndef _LINUX_DAX_H
+#define _LINUX_DAX_H
+
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <asm/pgtable.h>
+
+ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, loff_t,
+		  get_block_t, dio_iodone_t, int flags);
+int dax_clear_blocks(struct inode *, sector_t block, long size);
+int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
+int dax_truncate_page(struct inode *, loff_t from, get_block_t);
+int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
+		dax_iodone_t);
+int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
+		dax_iodone_t);
+int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
+#define dax_mkwrite(vma, vmf, gb, iod)		dax_fault(vma, vmf, gb, iod)
+#define __dax_mkwrite(vma, vmf, gb, iod)	__dax_fault(vma, vmf, gb, iod)
+
+#endif

include/linux/fs.h

···
 struct seq_file;
 struct workqueue_struct;
 struct iov_iter;
-struct vm_fault;
 
 extern void __init inode_init(void);
 extern void __init inode_init_early(void);
···
 		int whence, loff_t size);
 extern int generic_file_open(struct inode * inode, struct file * filp);
 extern int nonseekable_open(struct inode * inode, struct file * filp);
-
-ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, loff_t,
-		  get_block_t, dio_iodone_t, int flags);
-int dax_clear_blocks(struct inode *, sector_t block, long size);
-int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
-int dax_truncate_page(struct inode *, loff_t from, get_block_t);
-int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
-		dax_iodone_t);
-int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,
-		dax_iodone_t);
-int dax_pfn_mkwrite(struct vm_area_struct *, struct vm_fault *);
-#define dax_mkwrite(vma, vmf, gb, iod)		dax_fault(vma, vmf, gb, iod)
-#define __dax_mkwrite(vma, vmf, gb, iod)	__dax_fault(vma, vmf, gb, iod)
 
 #ifdef CONFIG_BLOCK
 typedef void (dio_submit_t)(int rw, struct bio *bio, struct inode *inode,