Re: [PATCH v3 2/2] quorum: Implement bdrv_co_pwrite_zeroes()

[Max Reitz]

On 13.11.20 17:07, Alberto Garcia wrote:
> On Fri 13 Nov 2020 12:49:04 PM CET, Max Reitz wrote:
> > On 11.11.20 17:53, Alberto Garcia wrote:
> > > This simply calls bdrv_co_pwrite_zeroes() in all children
> > >
> > > Signed-off-by: Alberto Garcia <berto@igalia.com>
> > > ---
> > >    block/quorum.c             | 18 ++++++++++++++++--
> > >    tests/qemu-iotests/312     |  7 +++++++
> > >    tests/qemu-iotests/312.out |  4 ++++
> > >    3 files changed, 27 insertions(+), 2 deletions(-)
> >
> > Should we set supported_zero_flags to something?  I think we can at
> > least set BDRV_REQ_NO_FALLBACK.  We could also try BDRV_REQ_FUA.
>
> We could set all supported_zero_flags as long as all children support
> them, right?

Sure, I was just thinking that we could set these regardless of whether 
the children support them, because (on zero-writes) the block layer will 
figure out for us whether the child nodes support them. O:)

> > > +    if (acb->flags & BDRV_REQ_ZERO_WRITE) {
> > > +        sacb->ret = bdrv_co_pwrite_zeroes(s->children[i], acb->offset,
> > > +                                          acb->bytes, acb->flags);
> > > +    } else {
> > > +        sacb->ret = bdrv_co_pwritev(s->children[i], acb->offset, acb->bytes,
> > > +                                    acb->qiov, acb->flags);
> > > +    }
> >
> > Seems unnecessary (bdrv_co_pwritev() can handle BDRV_REQ_ZERO_WRITE),
> > but perhaps it’s good to be explicit.
>
> pwrite_zeroes() does this additionaly:
>
>      if (!(child->bs->open_flags & BDRV_O_UNMAP)) {
>          flags &= ~BDRV_REQ_MAY_UNMAP;
>      }

Interesting.  Technically, Quorum doesn’t support that flag (in 
supported_zero_flags O:))), so it shouldn’t appear, but, er, well then.

Max