[PATCH V15 06/16] xfs: Check for extent overflow when renaming dir entries

[Chandan Babu R <chandanrlinux@gmail.com>]

A rename operation is essentially a directory entry remove operation
from the perspective of parent directory (i.e. src_dp) of rename's
source. 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.

Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
---
 fs/xfs/libxfs/xfs_bmap.c |  3 +++
 fs/xfs/xfs_inode.c       | 44 +++++++++++++++++++++++++++++++++++++++-
 2 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index 6c8f17a0e247..8ebe5f13279c 100644
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -5160,6 +5160,9 @@ xfs_bmap_del_extent_real(
 		 * 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) {
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 4cc787cc4eee..f0a6d528cbc4 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3116,6 +3116,35 @@ 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) {
 		/*
@@ -3126,6 +3155,12 @@ 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 {
 		/*
@@ -3283,9 +3318,16 @@ xfs_rename(
 	if (wip) {
 		error = xfs_dir_replace(tp, src_dp, src_name, wip->i_ino,
 					spaceres);
-	} else
+	} 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.
+		 */
 		error = xfs_dir_removename(tp, src_dp, src_name, src_ip->i_ino,
 					   spaceres);
+	}
+
 	if (error)
 		goto out_trans_cancel;
 
-- 
2.29.2