[libvirt] [PATCH 2/5] qemu: Store supported migration capabilities in a bitmap

[Jiri Denemark]

On Thu, Oct 19, 2017 at 18:30:53 -0400, John Ferlan wrote:
> 
> 
> On 10/18/2017 07:29 AM, Jiri Denemark wrote:
> > Each time we need to check whether a given migration capability is
> > supported by QEMU, we call query-migrate-capabilities QMP command and
> > lookup the capability in the returned list. Asking for the list of
> > supported capabilities once when we connect to QEMU and storing the
> > result in a bitmap is much better and we don't need to enter a monitor
> > just to check whether a migration capability is supported.
> > 
> > Signed-off-by: Jiri Denemark <jdenemar at redhat.com>
> > ---
> >  src/qemu/qemu_domain.c  | 68 +++++++++++++++++++++++++++++++++++++++++++++++++
> >  src/qemu/qemu_domain.h  |  9 +++++++
> >  src/qemu/qemu_process.c | 13 +---------
> >  3 files changed, 78 insertions(+), 12 deletions(-)
> > 
> 
> There's no corresponding adjustment to qemuDomainObjPrivateXMLFormat and
> qemuDomainObjPrivateXMLParse in order to handle the restart scenario.
> 
> The rest of this looks OK, but do you need the Format/Parse logic for
> the bitmap?

No. The migration capabilities are rechecked every time libvirt connects
to QEMU as said in the commit message and in qemu_domain.h:

> > diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
> > index 5201c6a0ac..fb20d8ea63 100644
> > --- a/src/qemu/qemu_domain.h
> > +++ b/src/qemu/qemu_domain.h
> > @@ -323,6 +323,10 @@ struct _qemuDomainObjPrivate {
> >  
> >      /* Tracks blockjob state for vm. Valid only while reconnecting to qemu. */
> >      virTristateBool reconnectBlockjobs;
> > +
> > +    /* Migration capabilities. Rechecked on reconnect, not to be saved in
> > +     * private XML. */
> > +    virBitmapPtr migrationCaps;
> >  };

Jirka