Re: incorrect disk numbering with qemu

[Olaf Hering <olaf@aepfle.de>]

On Wed, Jan 15, Ian Campbell wrote:

> On Wed, 2014-01-15 at 18:12 +0100, Olaf Hering wrote:
> > It seems qemu does not enumerate the configured disks correctly with a
> > config like this:
> > 
> > disk=[  
> >         'raw:/some.iso,hda:cdrom,r',
> >         'raw:/some.raw,xvda,w',
> > ]
> > 
> > With a PV guest it works fine, the guest has a hda and xvda device. 
> > But a HVM guest fails to start:
> > qemu-system-i386: -drive file=/some.raw,if=ide,index=0,media=disk,format=raw,cache=writeback: drive with bus=0, unit=0 (index=0) exists
> > 
> > I think that kind of config used to work with xend.
> 
> Did it? I thought xvda and hda were effectively considered two faces of
> the same device, so I'm not so sure. I'd be particularly surprised if
> this worked by design rather than coincidence.

Putting a 'device_model_version="qemu-xen-traditional"' into the config
fixes it for me.

So the question is how it is supposed to work. My understanding is that
for HVM some sort of IDE is (or was?) required to let it boot from a
block device. Thats why I have hd[abcd] as device name. In addition to
that one could have as many disks named xvd[abc..], which are PV only.

After some testing it seems that today the guest will boot from xvda,
even with qemu-xen-traditional. So either that got fixed with libxl, or
xend from 4.2 got it all wrong.

So what should be done with such configs, if they really exist in the
wild? The obvious workaround is device_model_version="qemu-xen-traditional".

Olaf