[PATCH v16 07/28] xfsprogs: Check for extent overflow when renaming dir entries

From: Allison Henderson <allison.henderson@oracle.com>
To: linux-xfs@vger.kernel.org
Subject: [PATCH v16 07/28] xfsprogs: Check for extent overflow when renaming dir entries
Date: Thu, 25 Mar 2021 17:31:10 -0700	[thread overview]
Message-ID: <20210326003131.32642-8-allison.henderson@oracle.com> (raw)
In-Reply-To: <20210326003131.32642-1-allison.henderson@oracle.com>

From: Chandan Babu R <chandanrlinux@gmail.com>

Source kernel commit: 02092a2f034fdeabab524ae39c2de86ba9ffa15a

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.

Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
---
 libxfs/xfs_bmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libxfs/xfs_bmap.c b/libxfs/xfs_bmap.c
index e3c6b0b..e9c9f45 100644
--- a/libxfs/xfs_bmap.c
+++ b/libxfs/xfs_bmap.c
@@ -5153,6 +5153,9 @@ 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) {
-- 
2.7.4

