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/ab5fc8a7d5ffccfd5f27b1cf2cb4ceb6c110da74.1536269131.git.ernesto.mnd.fernandez@gmail.com
Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfs/btree.c

@@ -220,6 +220,30 @@ static struct hfs_bnode *hfs_bmap_new_bmap(struct hfs_bnode *prev, u32 idx)
 	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;
@@ -229,26 +253,11 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree)
 	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);