Re: [PATCH v5 5/7] xfs: Support atomic write for statx

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

On Sat, Aug 17, 2024 at 09:47:58AM +0000, John Garry wrote:
> Support providing info on atomic write unit min and max for an inode.
> 
> For simplicity, currently we limit the min at the FS block size, but a
> lower limit could be supported in future. This is required by iomap
> DIO.
> 
> The atomic write unit min and max is limited by the guaranteed extent
> alignment for the inode.
> 
> Signed-off-by: John Garry <john.g.garry@oracle.com>
> ---
>  fs/xfs/xfs_iops.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
> index 6e017aa6f61d..c20becd3a7c9 100644
> --- a/fs/xfs/xfs_iops.c
> +++ b/fs/xfs/xfs_iops.c
> @@ -570,6 +570,27 @@ xfs_stat_blksize(
>  	return PAGE_SIZE;
>  }
>  
> +static void
> +xfs_get_atomic_write_attr(
> +	struct xfs_inode	*ip,
> +	unsigned int		*unit_min,
> +	unsigned int		*unit_max)
> +{
> +	struct xfs_buftarg	*target = xfs_inode_buftarg(ip);
> +	struct xfs_mount	*mp = ip->i_mount;
> +	struct xfs_sb		*sbp = &mp->m_sb;
> +	unsigned int		extsz_bytes = XFS_FSB_TO_B(mp, ip->i_extsize);
> +
> +	if (!xfs_inode_has_atomicwrites(ip)) {

Here's where you might want to check that DIFLAG2_ATOMICWRITES is sset
and stripe alignment still makes sense before handing out nonzero
STATX_WRITE_ATOMIC information.  The rest of the patch looks ok to me.

--D

> +		*unit_min = 0;
> +		*unit_max = 0;
> +		return;
> +	}
> +
> +	*unit_min = sbp->sb_blocksize;
> +	*unit_max = min(target->bt_bdev_awu_max, extsz_bytes);
> +}
> +
>  STATIC int
>  xfs_vn_getattr(
>  	struct mnt_idmap	*idmap,
> @@ -643,6 +664,13 @@ xfs_vn_getattr(
>  			stat->dio_mem_align = bdev_dma_alignment(bdev) + 1;
>  			stat->dio_offset_align = bdev_logical_block_size(bdev);
>  		}
> +		if (request_mask & STATX_WRITE_ATOMIC) {
> +			unsigned int unit_min, unit_max;
> +
> +			xfs_get_atomic_write_attr(ip, &unit_min, &unit_max);
> +			generic_fill_statx_atomic_writes(stat,
> +				unit_min, unit_max);
> +		}
>  		fallthrough;
>  	default:
>  		stat->blksize = xfs_stat_blksize(ip);
> -- 
> 2.31.1
> 
>