Re: qemu-nbd CMD_BLOCK_STATUS returns one extent in CentOS 8.0, all extents in 4.1.0 - is this a bug?

[Eric Blake]

On 11/27/19 12:43 PM, Richard W.M. Jones wrote:
> On Wed, Nov 27, 2019 at 08:06:43PM +0200, Nir Soffer wrote:
> > I have a failing test[1] of ovirt-imageio nbd client[2], getting
> > base:allocation from qemu-nbd.

> > The test fails because on CentOS 8, qemu-nbd returns:
> >
> >      {'base:allocation': [Extent(length=4096, zero=False)]}
> >
> > We send CMD_BLOCK_STATUS with flags=0 (NBD_CMD_FLAG_REQ_ONE not set).
> >
> > The tests fail with:
> > qemu-img-2.12.0-65.module_el8.0.0+189+f9babebb.5.x86_64
> >
> > And work with:
> > qemu-img-4.1.0-5.fc30.x86_64
>
> Could it be this fix which appeared in 3.1.0?
>
> commit fb7afc797e071f2616e1ccc849b39fe43e7033bf
> Author: Vladimir Sementsov-Ogievskiy <address@hidden>
> Date:   Wed Jul 4 14:23:02 2018 +0300
>
>      nbd/server: send more than one extent of base:allocation context
>      
>      This is necessary for efficient block-status export, for clients which
>      support it.  (qemu is not yet such a client, but could become one.)

Yes, that sounds very plausible.

> No idea if we're going to or even if we can fix this in RHEL non-AV or
> CentOS.

For backports, you're better off opening a bugzilla and letting Red 
Hat's process deal with the decision on whether to make the backport 
(here on the upstream list, the answer is obvious: use qemu 4.2 when it 
comes out ;)

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org