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

[Jim Fehlig]

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 at 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.

Regards,
Jim