Re: [PATCH V14 05/16] xfs: Check for extent overflow when removing dir entries

Darrick J. Wong
2021-01-12T01:39:09Z

On Sun, Jan 10, 2021 at 09:37:09PM +0530, Chandan Babu R wrote:
> Directory entry removal must always succeed; Hence XFS does the
> following during low disk space scenario:
> 1. Data/Free blocks linger until a future remove operation.
> 2. Dabtree blocks would be swapped with the last block in the leaf space
> and then the new last block will be unmapped.
>
> This facility is reused during low inode extent count scenario i.e. this
> commit causes xfs_bmap_del_extent_real() to return -ENOSPC error code so
> that the above mentioned behaviour is exercised causing no change to the
> directory's extent count.
>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>

Thanks for the minor tweaks since v12,

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

--D

> ---
> fs/xfs/libxfs/xfs_bmap.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 32aeacf6f055..6c8f17a0e247 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5151,6 +5151,24 @@ 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.
> + */
> + 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;
> --
> 2.29.2
>