Re: [libvirt] [PATCH v2 01/15] Add event and state details for post-copy

On Fri, Jan 22, 2016 at 04:17:42PM +0100, Jiri Denemark wrote: > On Fri, Jan 22, 2016 at 15:07:04 +0000, Daniel P. Berrange wrote: > > On Thu, Jan 21, 2016 at 11:20:46AM +0100, Jiri Denemark wrote: > > > VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY and VIR_DOMAIN_PAUSED_POSTCOPY are > > > used on the source host once migration enters post-copy mode (which > > > means the domain gets paused on the source. After the destination host > > > takes over the execution of the domain, its virtual CPUs are resumed and > > > the domain enters VIR_DOMAIN_RUNNING_POSTCOPY state and > > > VIR_DOMAIN_EVENT_RESUMED_POSTCOPY event is emitted. > > > > > > In case migration fails during post-copy mode and none of the hosts have > > > complete state of the domain, both domains will remain paused with > > > VIR_DOMAIN_PAUSED_POSTCOPY_FAILED reason and an upper layer may decide > > > what to do. > > > > > > Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; > > > > > @@ -2380,6 +2383,8 @@ typedef enum { > > > VIR_DOMAIN_EVENT_SUSPENDED_RESTORED = 4, /* Restored from paused state file */ > > > VIR_DOMAIN_EVENT_SUSPENDED_FROM_SNAPSHOT = 5, /* Restored from paused snapshot */ > > > VIR_DOMAIN_EVENT_SUSPENDED_API_ERROR = 6, /* suspended after failure during libvirt API call */ > > > + VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY = 7, /* suspended for post-copy migration */ > > > + VIR_DOMAIN_EVENT_SUSPENDED_POSTCOPY_FAILED = 8, /* suspended after failed post-copy */ > > > > Presumably the POSTCOPY_FAILED event can only be emitted > > on the target, since the source will already be suspended > > when we see a failure, and it doesn't make sense to issue > > a suspended event when we're already suspended. > > But would it cause any harm? I figured it might be better to emit the > event and set the state to POSTCOPY_FAILED even on the source so that > apps/users don't have to guess whether POSTCOPY means it's still running > or if it already failed. The lifecycle events are supposed to be implementing a state machine, and we're not changing state in this case. I think applications that are currently using libvirt would reasonably consider it an error if libvirt issues an event for a state it is already in, and I could see it causing them to mistakenly run some logic twice if they get two SUSPEND events for the same domain in a row.