[PATCH V14 06/16] xfs: Check for extent overflow when renaming dir entries

Chandan Babu R
2021-01-10T16:11:14Z

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>
---
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