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

[Stefan Bader]

On 25.03.2014 16:46, Daniel P. Berrange wrote:
> 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

All-right, thanks for confirming. :) Will work on that.

-Stefan
> 
> Regards,
> Daniel
> 


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