[libvirt] [PATCH v2] qemu_migration: Avoid crashing if domain dies too quickly

[Wangyufei (A)]

> -----Original Message-----
> From: Michal Privoznik [mailto:mprivozn at redhat.com]
> Sent: Friday, October 18, 2013 2:37 PM
> To: Wangyufei (A)
> Cc: libvir-list at redhat.com; Wangrui (K)
> Subject: Re: [libvirt] [PATCH v2] qemu_migration: Avoid crashing if domain
> dies too quickly
> 
> On 18.10.2013 08:22, Wangyufei (A) wrote:
> > I'm sorry. I didn't get what you mean.
> >
> > In virQEMUCapsInitQMP
> >
> >     if (!(xmlopt = virDomainXMLOptionNew(NULL, NULL, NULL)) ||
> >         !(vm = virDomainObjNew(xmlopt)))
> >         goto cleanup;
> >
> >     vm->pid = pid;   //Apparently vm is not NULL here.
> >
> >     if (!(mon = qemuMonitorOpen(vm, &config, true, &callbacks, NULL)))
> {  //If qemuMonitorOpen returns NULL here, but not do mon->vm =
> virObjectRef(vm); in qemuMonitorOpenInternal.
> >         ret = 0;
> >         goto cleanup;  // We go to cleanup here.
> >     }
> >
> >     virObjectLock(mon);
> >
> >     if (virQEMUCapsInitQMPMonitor(qemuCaps, mon) < 0)
> >         goto cleanup;
> >
> >     ret = 0;
> >
> > cleanup:
> >     if (mon)
> >         virObjectUnlock(mon);
> >     qemuMonitorClose(mon);
> >     virCommandAbort(cmd);
> >     virCommandFree(cmd);
> >     VIR_FREE(monarg);
> >     VIR_FREE(monpath);
> >     virObjectUnref(vm);    //vm is not NULL here, and we'll do
> something about vm->refs, right?
> 
> Yes. In fact we dispose @vm as we are the only one holding reference to
> it and we don't longer need it. If qemuMonitorOpenInternal would do
> virObjectRef(vm), then vm->refs = 2 before executing this line. After

If qemuMonitorOpenInternal did not do virObjectRef(vm) and return NULL before it, then vm->refs = 1 before executing this line. Right?
Now we do virObjectUnref(vm), vm will be disposed here, and that's we expected. Fine, I've got you. Thanks a lot.

> the execution, the refs is decremented to 1 as @mon is the only one
> holding reference to @vm.
> 
> >     virObjectUnref(xmlopt);