Re: [PATCH v3 3/3] xfs: reject max_atomic_write mount option for no reflink

[John Garry]

On 24/07/2025 17:32, Darrick J. Wong wrote:
> On Thu, Jul 24, 2025 at 08:12:15AM +0000, John Garry wrote:
> > If the FS has no reflink, then atomic writes greater than 1x block are not
> > supported. As such, for no reflink it is pointless to accept setting
> > max_atomic_write when it cannot be supported, so reject max_atomic_write
> > mount option in this case.
> >
> > It could be still possible to accept max_atomic_write option of size 1x
> > block if HW atomics are supported, so check for this specifically.
> >
> > Fixes: 4528b9052731 ("xfs: allow sysadmins to specify a maximum atomic write limit at mount time")
> > Signed-off-by: John Garry<john.g.garry@xxxxxxxxxx>
> /me wonders if "mkfs: allow users to configure the desired maximum
> atomic write size" needs a similar filter?

Yeah, probably. But I am wondering if we should always require reflink 
for setting that max atomic mkfs option, and not have a special case of 
HW atomics available for 1x blocksize atomic writes.

> Reviewed-by: "Darrick J. Wong"<djwong@xxxxxxxxxx>

cheers