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

Darrick J. Wong
2021-01-12T01:38:18Z

On Sun, Jan 10, 2021 at 09:37:10PM +0530, Chandan Babu R wrote:
> 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>

Looks good,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D

> ---
> 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
>