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

[Darrick J. Wong]

On Fri, Jul 25, 2025 at 09:39:42AM +0100, John Garry wrote:
> 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.

I think that's reasonable for mkfs since reflink=1 has been the default
for quite a long while now.

--D

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