[libvirt PATCH 54/80] qemu: Implement VIR_MIGRATE_POSTCOPY_RESUME for Begin phase

[Jiri Denemark]

On Wed, May 18, 2022 at 15:59:46 +0200, Peter Krempa wrote:
> On Wed, May 18, 2022 at 15:40:18 +0200, Jiri Denemark wrote:
> > On Thu, May 12, 2022 at 14:14:15 +0200, Peter Krempa wrote:
> > > > +static char *
> > > > +qemuMigrationSrcBeginResume(virQEMUDriver *driver,
> > > > +                            virDomainObj *vm,
> > > > +                            const char *xmlin,
> > > > +                            char **cookieout,
> > > > +                            int *cookieoutlen,
> > > > +                            unsigned long flags)
> > > > +{
> > > > +    virDomainJobStatus status;
> > > > +
> > > > +    if (qemuMigrationAnyRefreshStatus(driver, vm, VIR_ASYNC_JOB_MIGRATION_OUT,
> > > > +                                      &status) < 0)
> > > > +        return NULL;
> > > > +
> > > > +    if (status != VIR_DOMAIN_JOB_STATUS_POSTCOPY_PAUSED) {
> > > > +        virReportError(VIR_ERR_OPERATION_INVALID, "%s",
> > > > +                       _("QEMU reports migration is still running"));
> > > > +        return NULL;
> > > > +    }
> > > > +
> > > > +    return qemuMigrationSrcBeginXML(driver, vm, xmlin,
> > > > +                                    cookieout, cookieoutlen, 0, NULL, 0, flags);
> > > 
> > > Certain steps here around the non-shared-storage migration are redundant
> > > at this point and IMO should be skipped.
> > 
> > Which is what happens in qemuMigrationSrcBegin:
> > 
> >     if (flags & VIR_MIGRATE_POSTCOPY_RESUME) {
> >         xml = qemuMigrationSrcBeginResumePhase(...);
> >         goto cleanup;
> >     }
> > 
> >     ...
> > 
> > Or did I miss anything?
> 
> In 'qemuMigrationSrcBeginXML'
> qemuMigrationSrcBeginPhaseBlockDirtyBitmaps is called which does a bunch
> of setup for bitmap migration which is pointless when recovering as
> storage is copied already if the CPUs are running on the destination.

Oh I see. This part is actually skipped, although it is not easily
visible. The function is only called when QEMU_MIGRATION_COOKIE_NBD is
set in cookieFlags and qemuMigrationSrcBeginResume calls
qemuMigrationSrcBeginXML with cookieFlags == 0.

Jirka