hfs: prevent btree data loss on ENOSPC

Inserting a new record in a btree may require splitting several of its
nodes. If we hit ENOSPC halfway through, the new nodes will be left
orphaned and their records will be lost. This could mean lost inodes or
extents.

Henceforth, check the available disk space before making any changes.
This still leaves the potential problem of corruption on ENOMEM.

There is no need to reserve space before deleting a catalog record, as we
do for hfsplus. This difference is because hfs index nodes have fixed
length keys.

Link: http://lkml.kernel.org/r/ab5fc8a7d5ffc[e-mail]
Signed-off-by: Ernesto A. Fernández <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/hfs/btree.c

···
 	return node;
 }
 
+/* Make sure @tree has enough space for the @rsvd_nodes */
+int hfs_bmap_reserve(struct hfs_btree *tree, int rsvd_nodes)
+{
+	struct inode *inode = tree->inode;
+	u32 count;
+	int res;
+
+	while (tree->free_nodes < rsvd_nodes) {
+		res = hfs_extend_file(inode);
+		if (res)
+			return res;
+		HFS_I(inode)->phys_size = inode->i_size =
+				(loff_t)HFS_I(inode)->alloc_blocks *
+				HFS_SB(tree->sb)->alloc_blksz;
+		HFS_I(inode)->fs_blocks = inode->i_size >>
+					  tree->sb->s_blocksize_bits;
+		inode_set_bytes(inode, inode->i_size);
+		count = inode->i_size >> tree->node_size_shift;
+		tree->free_nodes += count - tree->node_count;
+		tree->node_count = count;
+	}
+	return 0;
+}
+
 struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree)
 {
 	struct hfs_bnode *node, *next_node;
···
 	u16 off16;
 	u16 len;
 	u8 *data, byte, m;
-	int i;
+	int i, res;
 
-	while (!tree->free_nodes) {
-		struct inode *inode = tree->inode;
-		u32 count;
-		int res;
-
-		res = hfs_extend_file(inode);
-		if (res)
-			return ERR_PTR(res);
-		HFS_I(inode)->phys_size = inode->i_size =
-				(loff_t)HFS_I(inode)->alloc_blocks *
-				HFS_SB(tree->sb)->alloc_blksz;
-		HFS_I(inode)->fs_blocks = inode->i_size >>
-					  tree->sb->s_blocksize_bits;
-		inode_set_bytes(inode, inode->i_size);
-		count = inode->i_size >> tree->node_size_shift;
-		tree->free_nodes = count - tree->node_count;
-		tree->node_count = count;
-	}
+	res = hfs_bmap_reserve(tree, 1);
+	if (res)
+		return ERR_PTR(res);
 
 	nidx = 0;
 	node = hfs_bnode_find(tree, nidx);

fs/hfs/btree.h

···
 extern struct hfs_btree *hfs_btree_open(struct super_block *, u32, btree_keycmp);
 extern void hfs_btree_close(struct hfs_btree *);
 extern void hfs_btree_write(struct hfs_btree *);
+extern int hfs_bmap_reserve(struct hfs_btree *, int);
 extern struct hfs_bnode * hfs_bmap_alloc(struct hfs_btree *);
 extern void hfs_bmap_free(struct hfs_bnode *node);
 

fs/hfs/catalog.c

···
 	if (err)
 		return err;
 
+	/*
+	 * Fail early and avoid ENOSPC during the btree operations. We may
+	 * have to split the root node at most once.
+	 */
+	err = hfs_bmap_reserve(fd.tree, 2 * fd.tree->depth);
+	if (err)
+		goto err2;
+
 	hfs_cat_build_key(sb, fd.search_key, cnid, NULL);
 	entry_size = hfs_cat_build_thread(sb, &entry, S_ISDIR(inode->i_mode) ?
 			HFS_CDR_THD : HFS_CDR_FTH,
···
 	if (err)
 		return err;
 	dst_fd = src_fd;
+
+	/*
+	 * Fail early and avoid ENOSPC during the btree operations. We may
+	 * have to split the root node at most once.
+	 */
+	err = hfs_bmap_reserve(src_fd.tree, 2 * src_fd.tree->depth);
+	if (err)
+		goto out;
 
 	/* find the old dir entry and read the data */
 	hfs_cat_build_key(sb, src_fd.search_key, src_dir->i_ino, src_name);

fs/hfs/extent.c

···
 	if (HFS_I(inode)->flags & HFS_FLG_EXT_NEW) {
 		if (res != -ENOENT)
 			return res;
+		/* Fail early and avoid ENOSPC during the btree operation */
+		res = hfs_bmap_reserve(fd->tree, fd->tree->depth + 1);
+		if (res)
+			return res;
 		hfs_brec_insert(fd, HFS_I(inode)->cached_extents, sizeof(hfs_extent_rec));
 		HFS_I(inode)->flags &= ~(HFS_FLG_EXT_DIRTY|HFS_FLG_EXT_NEW);
 	} else {