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

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(a)suse.com&gt; >> --- >> >> 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.