Re: [libvirt] [FOR 1.3.0 PATCH] conf: add net device prefix for Xen

[Joao Martins <joao.m.martins@oracle.com>]

On 12/08/2015 04:06 PM, Jim Fehlig wrote:
> Daniel P. Berrange wrote:
>> On Mon, Dec 07, 2015 at 10:59:32PM -0700, Jim Fehlig wrote:
>>> On 12/07/2015 11:52 AM, Daniel P. Berrange wrote:
>>>> On Mon, Dec 07, 2015 at 09:42:21AM -0700, Jim Fehlig wrote:
>>>>> In commit d2e5538b1, the libxl driver was changed to copy interface
>>>>> names autogenerated by libxl to the corresponding network def in the
>>>>> domain's virDomainDef object. The copied name is freed when the domain
>>>>> transitions to the shutoff state. But when migrating a domain, the
>>>>> autogenerated name is included in the XML sent to the destination host.
>>>>> It is possible an interface with the same name already exists on the
>>>>> destination host, causing migration to fail. Indeed the Xen project's
>>>>> OSSTEST CI already encountered such a failure.
>>>>>
>>>>> This patch defines another VIR_NET_GENERATED_PREFIX for Xen, allowing
>>>>> the autogenerated names to be excluded when parsing and formatting
>>>>> inactive config.
>>>>>
>>>>> Signed-off-by: Jim Fehlig <jfehlig@suse.com>
>>>>> ---
>>>>>
>>>>> This is an alternative approach to Joao's fix for this regression
>>>>>
>>>>> https://www.redhat.com/archives/libvir-list/2015-December/msg00197.html
>>>>>
>>>>> I think it is the same approach used by the qemu driver. My only
>>>>> reservation is that it expands the potential for clashes with
>>>>> user-defined names. I.e. with this change both 'vnet' and 'vif' are
>>>>> reserved prefixes.
>>>> Hmm, yes, tricky one.
>>>>
>>>> If we only care about XML parsing, then you could register a post
>>>> parse callback instead to do this.
>>> AFAIK, XML parsing is all that's in play here.
>>>
>>>> I'm not clear why we also have it in the virDomainNetDefFormat
>>>> method - and we can't solve that with a post-parse callback.
>>>>
>>>>
>>>> The other option would be to make the reserved prefix be a
>>>> capability that the parser/formatter could read.
>>> This seems like the best option, since a post-parse callback doesn't solve the
>>> problem in virDomainNetDefFormat. It also has the upshot of making the prefix
>>> visible and known to users. But I doubt such a change is suitable during 1.3.0
>>> freeze.  With the freeze in mind, seems the best solution to the libxl migration
>>> regression is revert d2e5538b1. It can be added again post-1.3.0 release, after
>>> adding the prefix to capabilities.
>>>
>>> DV, since you may be making the release soon, feel free to revert d2e5538b1 if
>>> you agree.
>>
>> Yeah, just go ahead & revert it Jim,  DV isn't doing the releae until
>> tomorrow morning
> 
> I've pushed the revert.
> 
> Joao, sorry for yanking this for 1.3.0. We can get it in 1.3.1, after exposing
> the prefix in capabilities.
> 
Hey Jim,

I had the impression we had pushed this back in (i.e. cherry-picking d2e5538)
but I was double checking and that's doesn't seem to be case. In adding support
for the prefix in capabilities I found out one issue on the migration failure
path leading to dereferencing a NULL pointer on the destination. If you agree
could we squash the following chunk in addition to the cherry-pick of d2e5538:

diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
index 63c5b24..f73bfb3 100644
--- a/src/libxl/libxl_domain.c
+++ b/src/libxl/libxl_domain.c
@@ -768,7 +768,7 @@ libxlDomainCleanup(libxlDriverPrivatePtr driver,
         for (i = 0; i < vm->def->nnets; i++) {
             virDomainNetDefPtr net = vm->def->nets[i];

-            if (STRPREFIX(net->ifname, "vif"))
+            if (net->ifname && STRPREFIX(net->ifname, "vif"))
                 VIR_FREE(net->ifname);
         }
     }
diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
index 3f4457f..5479441 100644
--- a/src/libxl/libxl_driver.c
+++ b/src/libxl/libxl_driver.c
@@ -5590,7 +5590,7 @@ static virHypervisorDriver libxlHypervisorDriver = {
     .domainGetJobStats = libxlDomainGetJobStats, /* 1.3.1 */
     .domainMemoryStats = libxlDomainMemoryStats, /* 1.3.0 */
     .domainGetCPUStats = libxlDomainGetCPUStats, /* 1.3.0 */
-    .domainInterfaceStats = libxlDomainInterfaceStats, /* 1.3.0 */
+    .domainInterfaceStats = libxlDomainInterfaceStats, /* 1.3.2 */
     .connectDomainEventRegister = libxlConnectDomainEventRegister, /* 0.9.0 */
     .connectDomainEventDeregister = libxlConnectDomainEventDeregister, /* 0.9.0 */
     .domainManagedSave = libxlDomainManagedSave, /* 0.9.2 */


Or do you think it should be deferred to 1.3.3 ?

Thanks,
Joao

> Regards,
> Jim
> 
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