[libvirt] libxl: Issues with virt-manager when used to manager Xen domains

[Daniel P. Berrange]

On Tue, Mar 25, 2014 at 04:42:25PM +0100, Stefan Bader wrote:
> On 25.03.2014 16:36, Daniel P. Berrange wrote:
> > On Tue, Mar 25, 2014 at 04:22:54PM +0100, Stefan Bader wrote:
> >> This started off with some regression testing after going forward to Xen-4.4. We
> >> currently would pair that with a libvirt version 1.2.2 and right now operations
> >> through virsh seem to be working (mostly) well. But when using virt-manager (not
> >> the most up-to-date versions but some combinations that quite likely will occur
> >> (0.9.1 and 0.9.5)) there are some issues.
> >>
> >> Two symptoms seem to be caused by the same underlying problem which is caused by
> >> the way virt-manager interacts with libvirt. That seems to be that virt-manager
> >> acquires a reference to virDomainPtr only once and then uses that for subsequent
> >> call. This is a problem because both virDomainPtr object and virDomainObjPtr
> >> objects contains a domid but only the latter gets updated.
> >>
> >> So both, creating a new guest (which must be a define step and then use the
> >> handle to start the guest) as well as rebooting a guest cause problems for
> >> virt-manager. Mainly because of libxlDomainGetInfo() which retrieves the
> >> virDomainObjPtr for a given virDommainPtr. Then checks the domain object to be
> >> active or not but uses the domid from the domain to call into libxl:
> >>
> >>     if (!(vm = libxlDomObjFromDomain(dom)))
> >>         goto cleanup;
> >>     ...
> >>     if (!virDomainObjIsActive(vm)) {
> >>         info->cpuTime = 0;
> >>         info->memory = vm->def->mem.cur_balloon;
> >>         info->maxMem = vm->def->mem.max_balloon;
> >>     } else {
> >>         if (libxl_domain_info(priv->ctx, &d_info, dom->id) != 0) {
> >>
> >> This fails either with dom->id being -1 (still) or using the old id from before
> >> the reboot. A dirty hack seems to avoid this:
> > 
> > Yep, this is a pretty commonly hit problem. The solution is to *never*
> > access dom->id in the driver code at all. eg In this code snippet above
> > you could use  vm->def->id instead which should be up to date.
> 
> OK, it just seems for something that should not be done, it is done plenty of
> times in the libxl_driver codebase right now. At least pause and unpause seem to
> do the same...

I expect those pretty much all need to be fixed

Regards,
Daniel
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