[libvirt PATCH v2 4/5] qemu_migration: get migration blockers before hardcoded checks

[Eugenio Perez Martin]

On Wed, Jul 20, 2022 at 12:31 PM Jiri Denemark <jdenemar at redhat.com> wrote:
>
> On Wed, Jul 20, 2022 at 11:11:53 +0200, Eugenio Pérez wrote:
> > since qemu 6.0, if migration is blocked for some reason, 'query-migrate'
> > will return an array of error strings describing the migration blockers.
> > This can be used to check whether there are any devices blocking
> > migration, etc.
> >
> > Enable qemuMigrationSrcIsAllowed to query it.
> >
> > Signed-off-by: Eugenio Pérez <eperezma at redhat.com>
> > ---
> >  src/qemu/qemu_migration.c | 33 +++++++++++++++++++++++++++++++++
> >  1 file changed, 33 insertions(+)
> >
> > diff --git a/src/qemu/qemu_migration.c b/src/qemu/qemu_migration.c
> > index b12cb518ee..4224339f39 100644
> > --- a/src/qemu/qemu_migration.c
> > +++ b/src/qemu/qemu_migration.c
> > @@ -1414,6 +1414,20 @@ qemuMigrationSrcIsAllowedHostdev(const virDomainDef *def)
> >      return true;
> >  }
> >
> > +static int
> > +qemuDomainGetMigrationBlockers(virQEMUDriver *driver,
> > +                               virDomainObj *vm,
> > +                               char ***blockers)
> > +{
> > +    qemuDomainObjPrivate *priv = vm->privateData;
> > +    int rc;
> > +
> > +    qemuDomainObjEnterMonitor(driver, vm);
> > +    rc = qemuMonitorGetMigrationBlockers(priv->mon, blockers);
> > +    qemuDomainObjExitMonitor(vm);
> > +
> > +    return rc;
> > +}
> >
> >  /**
> >   * qemuMigrationSrcIsAllowed:
> > @@ -1439,6 +1453,25 @@ qemuMigrationSrcIsAllowed(virQEMUDriver *driver,
> >      int nsnapshots;
> >      int pauseReason;
> >      size_t i;
> > +    int r;
> > +
> > +    /* Ask qemu if it have a migration blocker */
> > +    if (virQEMUCapsGet(priv->qemuCaps, QEMU_CAPS_MIGRATION_BLOCKED_REASONS)) {
> > +        g_auto(GStrv) blockers = NULL;
> > +        r = qemuDomainGetMigrationBlockers(driver, vm, &blockers);
> > +        if (r != 0) {
> > +            virReportError(VIR_ERR_OPERATION_INVALID,
> > +                           _("cannot migrate domain, %s"),
> > +                           _("error getting blockers"));
>
> If qemuDomainGetMigrationBlockers returned -1 a better error message
> should already be set and you would overwrite it here. Also with your
> current patch you would report this error even in case there was no
> migration blocker reported by QEMU. But this part would be fixed by
> letting qemuDomainGetMigrationBlockers return 0 when the blocked-reasons
> field is missing.
>

Got it.

> > +            return false;
> > +        }
> > +
> > +        if (blockers[0]) {
>
> blockers && blockers[0]
>
> > +            virReportError(VIR_ERR_OPERATION_INVALID,
> > +                           _("cannot migrate domain, %s"), blockers[0]);
>
> I would prefer a colon there: "cannot migrate domain: %s". And we got a
> list of blockers from QEMU, but only use the first one? Please, join
> them with g_strjoinv().
>

So the resulting message should be:
"cannot migrate domain: <error1>, <error2>, ..., <errorN>", right?

Thanks!

> > +            return false;
> > +        }
> > +    }
> >
> >      /* perform these checks only when migrating to remote hosts */
> >      if (remote) {
>
> Jirka
>