[Libvir] Supporting new Xen 3.0.3 blktap backend for file devices

[Daniel P. Berrange]

On Wed, Sep 27, 2006 at 01:16:17PM -0400, Daniel Veillard wrote:
> On Wed, Sep 27, 2006 at 07:05:38PM +0200, Karel Zak wrote:
> > On Tue, Sep 26, 2006 at 08:08:33PM +0100, Daniel P. Berrange wrote:
> > > 
> > > This means the easy option of just making all file devices use blktap in
> > > 3.0.3 is not practical. This in turns means we need to  come up with a
> > > way to express the new driver methods in libvirt XML. There are a few
> > > options I can think of :
> > > 
> > >  - Allow more values in the 'type' attribute, eg file, block, blktap:aio,
> > >    blktap:qcow, etc. This feels wrong because the blktap:* entries are
> > >    really still 'file' types.
> > > 
> > >  - Introduce a new attribute  'driver'  where you can specify 'loop',
> > >    'blktap:aio', 'blktap:qcow', etc
> > > 
> > >  - Introduce a new element 'driver' where you can specify the same
> > > 
> > >        <disk type="file">
> > >           <driver type='blktap:aio'/>
> > >        </disk>
> > > 
> > >  - Same as above, but normalize the driver type further
> > > 
> > >        <disk type="file">
> > >          <driver type='blktap' backend='aio' />
> > >        </disk>
> > > 
> > > My preference is probably option 3 or 4.
> > 
> >  My preference is definitely 4.
> >  
> >  (well, I'm affected by Database Normalization where it's bad merge
> >  two information into one attribute -- so 'blktap:aio' is wrong way
> >  ;-)
> 
>   I would agree that rather than glueing it's better to separate the 2 strings
> as separate attributes. But should the second be named 'backend' or something
> more generic like 'subtype'. That's the only slight concern I have but it's
> probably better to be explicit about and the suggested form is just fine.
> Let's go for 4/ :-)

Ok, looks like we have total agreement. I'll knock up a patch implementing
option #4 and post it for review.

Dan.
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