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[Qemu-devel] Re: [PATCH] migration: Issue 'cont' only on successful inco


From: Laine Stump
Subject: [Qemu-devel] Re: [PATCH] migration: Issue 'cont' only on successful incoming migration
Date: Mon, 26 Jul 2010 11:27:59 -0400
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.4) Gecko/20100624 Fedora/3.1-1.fc13 Thunderbird/3.1

 On 07/26/2010 10:23 AM, Luiz Capitulino wrote:
On Sat, 24 Jul 2010 13:01:24 +0530
Amit Shah<address@hidden>  wrote:

On (Fri) Jul 23 2010 [15:08:18], Luiz Capitulino wrote:
diff --git a/monitor.c b/monitor.c
index 45fd482..d12a7b5 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1056,6 +1056,10 @@ static int do_cont(Monitor *mon, const QDict *qdict, 
QObject **ret_data)
  {
      struct bdrv_iterate_context context = { mon, 0 };

+    if (incoming_expected&&  !incoming_done) {
+        autostart = 1;
Why do we need to set autostart? We should just fail if we're unable to run.

+        return 1; /* Waiting for incoming migration */
You should return -1 and use qerror_report(), so that we have a meaningful
error in the user Monitor and QMP (otherwise we'll get UndefinedError).
That would mean old/existing libvirt will be confused on why guests
wouldn't start even though it issued cont.
Yes, although delaying to start could cause a problem too and this is
also introducing an new error in QMP already.

I really would like to avoid adding weird semantics, specially in QMP where
cont will return an error but will put the VM to run later. We could fix this
there only, but then it will get complex w/o reason.

We should fix it properly right now, IMO.

If it's not a problem for the libvirt folks, I can do that.
Laine, could you please check that?

That should really be answered by someone who better understands the implications (I'm a newcomer to that part of the code). Dan Berrange or Chris Lalancette maybe?

(I am setting up to test the current version of the patch on the system where I can reproduce the problem. Haven't flipped the switch yet, though.)



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