[libvirt] [PATCH] qemu: Allow empty script path to <interface/>

[Daniel P. Berrange]

On Thu, Feb 02, 2017 at 04:55:29PM +0100, Kashyap Chamarthy wrote:
> On Thu, Feb 02, 2017 at 03:29:15PM +0000, Daniel P. Berrange wrote:
> > On Thu, Feb 02, 2017 at 04:21:39PM +0100, Michal Privoznik wrote:
> > > On 02/02/2017 02:56 PM, Daniel P. Berrange wrote:
> > > > On Thu, Feb 02, 2017 at 02:49:48PM +0100, Michal Privoznik wrote:
> > > >> Before 9c17d665fdc5f (v1.3.2 - I know, right?) it was possible to
> > > >> have the following interface configuration:
> > > >>
> > > >>   <interface type='ethernet'/>
> > > >>     <script path=''/>
> > > >>   </interface>
> > > >>
> > > >> This resulted in -netdev tap,script=,.. Fortunately, qemu helped
> > > >> us to get away with this as it just ignored the empty script
> > > >> path. However, after the commit mentioned above it's libvirtd
> > > >> who is executing the script. Unfortunately without special
> > > >> case-ing empty script path.
> > > >>
> > > >> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> > > > 
> > > > This was always invalid input and the fact that it happened
> > > > to work in the past is just luck. Since this has been broken since
> > > > 1.3.2 there's plenty of libvirt releases that reject this, and so
> > > > any app realistically has to be fixed to omit the <script> entirely
> > > > if they want any portability. As such I don't think we need to "fix"
> > > > this.
> > > 
> > > Fair enough. Although, 1.3.2 was not that long time ago (~a year). BTW:
> > > it's openstack who is still using this.
> > > 
> > > https://bugzilla.redhat.com/show_bug.cgi?id=1412834
> 
> IIUC, this bug was filed to handle the case of _existing_ VMs that were
> not launched with the patch that you point to below.

THat is only a problem if you have a running VM on libvirt < 1.3.2 and
you want to migrate it to libvirt >= 1.3.2. That can be solved by
removing the bogus script element prior to migration - nova already
has code that modifies the XML prior to migration where such a fix
could live

Regards,
Daniel
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