[libvirt] [PATCH v2] libxl: free ifname on libxlDomainMigrationPrepareDef

[Jim Fehlig]

On 12/06/2015 10:04 AM, Jim Fehlig wrote:
> On 12/04/2015 12:45 PM, Joao Martins wrote:
>> Commit d2e5538b1 changes virDomainDef to include ifnames
>> that autogenerated by libxl, and that are also cleared
>> on domain cleanup. One place that's missing is on
>> migration, when domain xml is sent to dst libvirtd and
>> would contain ifnames from the source libvirtd. This
>> would lead to erronous behaviour (as seen in osstest CI)
>> such as failing to migrate when a vif with the same name
>> existed (belonging to another domain) on destination.
> Your patch is certainly one way to fix this issue, but I wonder if we should be
> adding the generated ifname to the XML that is sent to the destination.
> virDomainNetDefFormat() has this interesting piece of logic
>
>     if (def->ifname &&
>         !((flags & VIR_DOMAIN_DEF_FORMAT_INACTIVE) &&
>           (STRPREFIX(def->ifname, VIR_NET_GENERATED_PREFIX)))) {
>         /* Skip auto-generated target names for inactive config. */
>         virBufferEscapeString(buf, "<target dev='%s'/>\n", def->ifname);
>     }
>
> In the Begin phase, we format the XML that will be sent to the destination based
> on current vm->def of the machine running on the source. Calling
> virDomainDefFormat() with VIR_DOMAIN_DEF_FORMAT_INACTIVE doesn't seem right. I
> tried to see how this is handled in the qemu driver, but couldn't quite figure
> it out. Jirka is one of the experts of the qemu migration code, adding him to cc
> to see if he has any insights.

I think this is actually handled on the destination when parsing the incoming
XML in the Prepare phase. Something like the below patch may be a better solution.

Regards,
Jim

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