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

["Darrick J. Wong" <djwong@kernel.org>]

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
>