Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/6] rbd: Switch to byte-based callbacks

[Kevin Wolf <kwolf@redhat.com>]

Am 24.04.2018 um 21:53 hat Jason Dillaman geschrieben:
> On Tue, Apr 24, 2018 at 3:25 PM, Eric Blake <eblake@redhat.com> wrote:
> > We are gradually moving away from sector-based interfaces, towards
> > byte-based.  Make the change for the last few sector-based callbacks
> > in the rbd driver.
> >
> > Note that the driver was already using byte-based calls for
> > performing actual I/O, so this just gets rid of a round trip
> > of scaling; however, as I don't know if RBD is tolerant of
> > non-sector AIO operations, I went with the conservate approach
> > of adding .bdrv_refresh_limits to override the block layer
> > defaults back to the pre-patch value of 512.
> >
> > Signed-off-by: Eric Blake <eblake@redhat.com>
> >
> > ---
> > v2: override new block layer default alignment [Kevin]
> > ---
> >  block/rbd.c | 44 ++++++++++++++++++++++++--------------------
> >  1 file changed, 24 insertions(+), 20 deletions(-)
> >
> > diff --git a/block/rbd.c b/block/rbd.c
> > index c9359d0ad84..638ecf8d986 100644
> > --- a/block/rbd.c
> > +++ b/block/rbd.c
> > @@ -231,6 +231,13 @@ done:
> >  }
> >
> >
> > +static void qemu_rbd_refresh_limits(BlockDriverState *bs, Error **errp)
> > +{
> > +    /* XXX Does RBD support AIO on less than 512-byte alignment? */
> 
> Yes, librbd internally supports 1-byte alignment for IO, but the
> optimal alignment/length would be object size * stripe count.

Would you like to post a follow-up patch to this series that removes the
.bdrv_refresh_limits implementation again with a commit message
explaining that RBD does support byte alignment?

Kevin