Re: 4.7 qemu regression: HVM guests fail to boot from xvda

[Wei Liu <wei.liu2@citrix.com>]

On Tue, May 31, 2016 at 01:00:45PM +0100, George Dunlap wrote:
> On Tue, May 31, 2016 at 12:41 PM, Olaf Hering <olaf@aepfle.de> wrote:
> > On Tue, May 31, George Dunlap wrote:
> >
> >> Sorry, can you expand on this a bit?  Are you saying that on SuSE, if
> >> you specify "vdev=xvda" in your config file, that you'll get PV
> >> devices named "/dev/xvda", but that if you specify "vdev=hda", that
> >> you'll get PV devices but named "/dev/hda"?
> >
> > Yes, thats exactly what the xenlinux block frontend does.
> > pvops forces xvda, independent of the name 'vdev' in domU.cfg.
> > Up to xen-4.2 'vdev=hd*' was required to tell qemu to create an emulated
> > disk to boot from. Starting with xen-4.3 qemu also recognized
> > 'vdev=xvd*' for the emulated disk. And starting with xen-4.7 qemu
> > requires 'xvda=hd*' again.
> >
> > I think if some domU.cfg for xen-4.3+ has 'vdev=xvd*' and the domU uses
> > for some reason kernel names in config files and the domU uses a
> > xenlinux kernel, then changing domU.cfg to 'hd*' will allow the guest to
> > boot again. But its userland will miss the /dev/xvd* device nodes.
> > That probably remained unnoticed during testing the referenced commit if
> > a pvops based kernel was used.
> 
> Or if -- as is the case for most of my own test systems -- filesystem
> UUIDs are used rather than device names.  (This means things work the
> same on PV with PV disks, HVM with PV disks, and HVM with emulated
> disks -- for instance, if you're using nested virtualization and your
> L1 dom0 can't access L0 xenbus.)
> 
> Do you have a concrete proposal?
> 
> Anthony, does the OVMF-with-pv-only-drivers actually still work at the moment?
> 

It works. We got pushes to our ovmf tree regularly (only now it fails on
merlot).

Having an extra emulated device shouldn't break OVMF, we've had that for
a long time before that patch was applied.

So I think the safest option now is to revert the said patch and figure
out what to do next.

Anthony and Ian, what do you think?

Wei.

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