[libvirt] [PATCH] Add --downtime option to virsh migrate command

[Jiri Denemark]

> > @@ -2794,6 +2799,19 @@ cmdMigrate (vshControl *ctl, const vshCmd *cmd)
> >     if (vshCommandOptBool (cmd, "suspend"))
> >         flags |= VIR_MIGRATE_PAUSED;
> >
> > +    downtime = vshCommandOptFloat(cmd, "downtime", &found);
> > +    if (found) {
> > +        unsigned long long nanoseconds = downtime * 1e9;
> > +
> > +        if (nanoseconds <= 0) {
> > +            vshError(ctl, "%s", _("migrate: Invalid downtime"));
> > +            goto done;
> > +        }
> > +
> > +        if (virDomainMigrateSetDowntime(dom, nanoseconds))
> 
> Is this persistent, or only valid for the next migration? For example,
> I do a migration with --downtime and afterwards I do another migration
> with the same domain, but this time I don't specify a downtime. Would
> the first downtime still apply to the second migration?

Actually, this is a very good question since it reveals the API wasn't
designed well enough. Current implementation doesn't do much with the value
passed to virDomainMigrateSetDowntime, it just sends it to the appropriate
hypervisor (if it supports such functionality). In other words, the behavior
may differ for different hypervisors. Which doesn't seem to be a good thing
for a libvirt's public API. So we should decide whether the effect of calling
this API should be one-time or persistent and emulate that behavior for
hypervisors which don't support it. We also need flags parameter so that we
can change that behavior in the future.

Opinions?

Jirka