Re: [PATCH v8 5/7] xfs: Support atomic write for statx

[John Garry]

On 15/10/2024 13:15, Christoph Hellwig wrote:
> On Tue, Oct 15, 2024 at 09:01:40AM +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. As for
> > max, we limit also at FS block size, as there is no current method to
> > guarantee extent alignment or granularity for regular files.
> >
> > Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
> > Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
> > ---
> >   fs/xfs/xfs_buf.c   |  7 +++++++
> >   fs/xfs/xfs_buf.h   |  3 +++
> >   fs/xfs/xfs_inode.h | 15 +++++++++++++++
> >   fs/xfs/xfs_iops.c  | 25 +++++++++++++++++++++++++
> >   4 files changed, 50 insertions(+)
> >
> > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
> > index aa4dbda7b536..e279e5e139ff 100644
> > --- a/fs/xfs/xfs_buf.c
> > +++ b/fs/xfs/xfs_buf.c
> > @@ -2115,6 +2115,13 @@ xfs_alloc_buftarg(
> >   	btp->bt_daxdev = fs_dax_get_by_bdev(btp->bt_bdev, &btp->bt_dax_part_off,
> >   					    mp, ops);
> >   
> > +	if (bdev_can_atomic_write(btp->bt_bdev)) {
> > +		struct request_queue *q = bdev_get_queue(btp->bt_bdev);
> > +
> > +		btp->bt_bdev_awu_min = queue_atomic_write_unit_min_bytes(q);
> > +		btp->bt_bdev_awu_max = queue_atomic_write_unit_max_bytes(q);
>
> Consumers of the block layer should never see request_queue.  While there
> is a few leftovers still I've cleaned most of this up.  Please add
> bdev_atomic_write_unit_min_bytes and bdev_atomic_write_unit_max_bytes
> helpers for use by file systems and stacking drivers, similar to the
> other queue limits.

ok, fine

> > +	/* Atomic write unit values */
> > +	unsigned int		bt_bdev_awu_min, bt_bdev_awu_max;
>
> Nit: While having two struct members declare on the same line using the
> same type specification is perfectly valid C, it looks odd and we avoid
> it in XFS (and most of the kernel).  Please split this into two lines.

sure

> > +	struct xfs_mount	*mp = ip->i_mount;
> > +	struct xfs_sb		*sbp = &mp->m_sb;
> > +
> > +	if (!xfs_inode_can_atomicwrite(ip)) {
> > +		*unit_min = *unit_max = 0;
> > +		return;
> > +	}
> > +
> > +	*unit_min = *unit_max = sbp->sb_blocksize;
>
> Nit: I'd do with the single use sbp local variable here.

I think that you mean do without.

> > +}
> > +
> >   STATIC int
> >   xfs_vn_getattr(
> >   	struct mnt_idmap	*idmap,
> > @@ -643,6 +660,14 @@ 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;
>
> Nit: XFS (unlike the rest of the kernel) uses tab alignments for
> variables.

ok

> Otherwise this looks good:
>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>

cheers