xfs: Directory's data fork extent counter can never overflow

The maximum file size that can be represented by the data fork extent counter
in the worst case occurs when all extents are 1 block in length and each block
is 1KB in size.

With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and with
1KB sized blocks, a file can reach upto,
(2^31) * 1KB = 2TB

This is much larger than the theoretical maximum size of a directory
i.e. XFS_DIR2_SPACE_SIZE * 3 = ~96GB.

Since a directory's inode can never overflow its data fork extent counter,
this commit removes all the overflow checks associated with
it. xfs_dinode_verify() now performs a rough check to verify if a diretory's
data fork is larger than 96GB.

Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandan.babu@oracle.com>

Author: Chandan Babu R

fs/xfs/libxfs/xfs_bmap.c

@@ -5147,26 +5147,6 @@ xfs_bmap_del_extent_real(
 		 * Deleting the middle of the extent.
 		 */
 
-		/*
-		 * For directories, -ENOSPC is returned since a directory entry
-		 * remove operation must not fail due to low extent count
-		 * availability. -ENOSPC will be handled by higher layers of XFS
-		 * by letting the corresponding empty Data/Free blocks to linger
-		 * until a future remove operation. Dabtree blocks would be
-		 * swapped with the last block in the leaf space and then the
-		 * new last block will be unmapped.
-		 *
-		 * The above logic also applies to the source directory entry of
-		 * a rename operation.
-		 */
-		error = xfs_iext_count_may_overflow(ip, whichfork, 1);
-		if (error) {
-			ASSERT(S_ISDIR(VFS_I(ip)->i_mode) &&
-				whichfork == XFS_DATA_FORK);
-			error = -ENOSPC;
-			goto done;
-		}
-
 		old = got;
 
 		got.br_blockcount = del->br_startoff - got.br_startoff;

fs/xfs/libxfs/xfs_da_btree.h

@@ -30,6 +30,7 @@ struct xfs_da_geometry {
 	unsigned int	free_hdr_size;	/* dir2 free header size */
 	unsigned int	free_max_bests;	/* # of bests entries in dir2 free */
 	xfs_dablk_t	freeblk;	/* blockno of free data v2 */
+	xfs_extnum_t	max_extents;	/* Max. extents in corresponding fork */
 
 	xfs_dir2_data_aoff_t data_first_offset;
 	size_t		data_entry_offset;

fs/xfs/libxfs/xfs_da_format.h

@@ -277,6 +277,7 @@ xfs_dir2_sf_firstentry(struct xfs_dir2_sf_hdr *hdr)
  * Directory address space divided into sections,
  * spaces separated by 32GB.
  */
+#define	XFS_DIR2_MAX_SPACES	3
 #define	XFS_DIR2_SPACE_SIZE	(1ULL << (32 + XFS_DIR2_DATA_ALIGN_LOG))
 #define	XFS_DIR2_DATA_SPACE	0
 #define	XFS_DIR2_DATA_OFFSET	(XFS_DIR2_DATA_SPACE * XFS_DIR2_SPACE_SIZE)

fs/xfs/libxfs/xfs_dir2.c

@@ -150,6 +150,8 @@ xfs_da_mount(
 	dageo->freeblk = xfs_dir2_byte_to_da(dageo, XFS_DIR2_FREE_OFFSET);
 	dageo->node_ents = (dageo->blksize - dageo->node_hdr_size) /
 				(uint)sizeof(xfs_da_node_entry_t);
+	dageo->max_extents = (XFS_DIR2_MAX_SPACES * XFS_DIR2_SPACE_SIZE) >>
+					mp->m_sb.sb_blocklog;
 	dageo->magicpct = (dageo->blksize * 37) / 100;
 
 	/* set up attribute geometry - single fsb only */
@@ -161,6 +163,12 @@ xfs_da_mount(
 	dageo->node_hdr_size = mp->m_dir_geo->node_hdr_size;
 	dageo->node_ents = (dageo->blksize - dageo->node_hdr_size) /
 				(uint)sizeof(xfs_da_node_entry_t);
+
+	if (xfs_has_large_extent_counts(mp))
+		dageo->max_extents = XFS_MAX_EXTCNT_ATTR_FORK_LARGE;
+	else
+		dageo->max_extents = XFS_MAX_EXTCNT_ATTR_FORK_SMALL;
+
 	dageo->magicpct = (dageo->blksize * 37) / 100;
 	return 0;
 }

fs/xfs/libxfs/xfs_format.h

@@ -915,6 +915,19 @@ enum xfs_dinode_fmt {
  *
  * Rounding up 47 to the nearest multiple of bits-per-byte results in 48. Hence
  * 2^48 was chosen as the maximum data fork extent count.
+ *
+ * The maximum file size that can be represented by the data fork extent counter
+ * in the worst case occurs when all extents are 1 block in length and each
+ * block is 1KB in size.
+ *
+ * With XFS_MAX_EXTCNT_DATA_FORK_SMALL representing maximum extent count and
+ * with 1KB sized blocks, a file can reach upto,
+ * 1KB * (2^31) = 2TB
+ *
+ * This is much larger than the theoretical maximum size of a directory
+ * i.e. XFS_DIR2_SPACE_SIZE * XFS_DIR2_MAX_SPACES = ~96GB.
+ *
+ * Hence, a directory inode can never overflow its data fork extent counter.
  */
 #define XFS_MAX_EXTCNT_DATA_FORK_LARGE	((xfs_extnum_t)((1ULL << 48) - 1))
 #define XFS_MAX_EXTCNT_ATTR_FORK_LARGE	((xfs_extnum_t)((1ULL << 32) - 1))

fs/xfs/libxfs/xfs_inode_buf.c

@@ -491,6 +491,9 @@ xfs_dinode_verify(
 	if (mode && nextents + naextents > nblocks)
 		return __this_address;
 
+	if (S_ISDIR(mode) && nextents > mp->m_dir_geo->max_extents)
+		return __this_address;
+
 	if (mode && XFS_DFORK_BOFF(dip) > mp->m_sb.sb_inodesize)
 		return __this_address;
 

fs/xfs/libxfs/xfs_inode_fork.h

@@ -39,19 +39,6 @@ struct xfs_ifork {
  */
 #define XFS_IEXT_PUNCH_HOLE_CNT		(1)
 
-/*
- * Directory entry addition can cause the following,
- * 1. Data block can be added/removed.
- *    A new extent can cause extent count to increase by 1.
- * 2. Free disk block can be added/removed.
- *    Same behaviour as described above for Data block.
- * 3. Dabtree blocks.
- *    XFS_DA_NODE_MAXDEPTH blocks can be added. Each of these can be new
- *    extents. Hence extent count can increase by XFS_DA_NODE_MAXDEPTH.
- */
-#define XFS_IEXT_DIR_MANIP_CNT(mp) \
-	((XFS_DA_NODE_MAXDEPTH + 1 + 1) * (mp)->m_dir_geo->fsbcount)
-
 /*
  * Adding/removing an xattr can cause XFS_DA_NODE_MAXDEPTH extents to
  * be added. One extra extent for dabtree in case a local attr is

fs/xfs/xfs_inode.c

@@ -1024,11 +1024,6 @@ xfs_create(
 	xfs_ilock(dp, XFS_ILOCK_EXCL | XFS_ILOCK_PARENT);
 	unlock_dp_on_error = true;
 
-	error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
-			XFS_IEXT_DIR_MANIP_CNT(mp));
-	if (error)
-		goto out_trans_cancel;
-
 	/*
 	 * A newly created regular or special file just has one directory
 	 * entry pointing to them, but a directory also the "." entry
@@ -1242,11 +1237,6 @@ xfs_link(
 	if (error)
 		goto std_return;
 
-	error = xfs_iext_count_may_overflow(tdp, XFS_DATA_FORK,
-			XFS_IEXT_DIR_MANIP_CNT(mp));
-	if (error)
-		goto error_return;
-
 	/*
 	 * If we are using project inheritance, we only allow hard link
 	 * creation in our tree when the project IDs are the same; else
@@ -3210,35 +3200,6 @@ xfs_rename(
 	/*
 	 * Check for expected errors before we dirty the transaction
 	 * so we can return an error without a transaction abort.
-	 *
-	 * Extent count overflow check:
-	 *
-	 * From the perspective of src_dp, a rename operation is essentially a
-	 * directory entry remove operation. Hence the only place where we check
-	 * for extent count overflow for src_dp is in
-	 * xfs_bmap_del_extent_real(). xfs_bmap_del_extent_real() returns
-	 * -ENOSPC when it detects a possible extent count overflow and in
-	 * response, the higher layers of directory handling code do the
-	 * following:
-	 * 1. Data/Free blocks: XFS lets these blocks linger until a
-	 *    future remove operation removes them.
-	 * 2. Dabtree blocks: XFS swaps the blocks with the last block in the
-	 *    Leaf space and unmaps the last block.
-	 *
-	 * For target_dp, there are two cases depending on whether the
-	 * destination directory entry exists or not.
-	 *
-	 * When destination directory entry does not exist (i.e. target_ip ==
-	 * NULL), extent count overflow check is performed only when transaction
-	 * has a non-zero sized space reservation associated with it.  With a
-	 * zero-sized space reservation, XFS allows a rename operation to
-	 * continue only when the directory has sufficient free space in its
-	 * data/leaf/free space blocks to hold the new entry.
-	 *
-	 * When destination directory entry exists (i.e. target_ip != NULL), all
-	 * we need to do is change the inode number associated with the already
-	 * existing entry. Hence there is no need to perform an extent count
-	 * overflow check.
 	 */
 	if (target_ip == NULL) {
 		/*
@@ -3249,12 +3210,6 @@ xfs_rename(
 			error = xfs_dir_canenter(tp, target_dp, target_name);
 			if (error)
 				goto out_trans_cancel;
-		} else {
-			error = xfs_iext_count_may_overflow(target_dp,
-					XFS_DATA_FORK,
-					XFS_IEXT_DIR_MANIP_CNT(mp));
-			if (error)
-				goto out_trans_cancel;
 		}
 	} else {
 		/*
@@ -3422,18 +3377,12 @@ xfs_rename(
 	 * inode number of the whiteout inode rather than removing it
 	 * altogether.
 	 */
-	if (wip) {
+	if (wip)
 		error = xfs_dir_replace(tp, src_dp, src_name, wip->i_ino,
 					spaceres);
-	} else {
-		/*
-		 * NOTE: We don't need to check for extent count overflow here
-		 * because the dir remove name code will leave the dir block in
-		 * place if the extent count would overflow.
-		 */
+	else
 		error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
 					   spaceres);
-	}
 
 	if (error)
 		goto out_trans_cancel;

fs/xfs/xfs_symlink.c

@@ -226,11 +226,6 @@ xfs_symlink(
 		goto out_trans_cancel;
 	}
 
-	error = xfs_iext_count_may_overflow(dp, XFS_DATA_FORK,
-			XFS_IEXT_DIR_MANIP_CNT(mp));
-	if (error)
-		goto out_trans_cancel;
-
 	/*
 	 * Allocate an inode for the symlink.
 	 */