libvirt 0.7.7 and Lucid

Scott Moser smoser at
Thu Apr 1 18:01:12 UTC 2010

On Wed, 31 Mar 2010, Dustin Kirkland wrote:
> On Thu, Mar 25, 2010 at 1:09 PM, Jamie Strandboge <jamie at> wrote:
> > 3. libvirt seems to try to guard against hypervisor issues regarding
> > detach-device and detach-disk. Specifically, these can be hot-plugged,
> > but not hot-unplugged (libvirt claims the qemu-kvm hypervisor doesn't
> > support detach of these):
> >    <disk type='block' device='disk'>
> >      <driver name='phy'/>
> >      <source dev='...path.../device_disk.img'/>
> >      <target dev='sdb' bus='scsi'/>
> >      <alias name='scsi0-0-1'/>
> >      <address type='drive' controller='0' bus='0' unit='1'/>
> >    </disk>

hotplug attach and detach of scsi driver disks is an absolute requirement
for UEC with Eucalyptus 1.6.2.  It is the basis of the "EBS" (Elastic
Block Store) functionality (euca-attach-volume, euca-detach-volume).

Our kernel team recently fixed bug 458201 so the user no longer sees scary
messages in dmesg when they *do* detach.  In my [limited]
experience/discussion with kvm folks it is generally accepted that scsi
device emulation is to be avoided.  However, we're stuck with it for now.

> As for virtio, we're planning to file a blueprint for Lucid+1 and try
> to get UEC using virtio for networking and disks.

Heres to hoping we can do something here.

> > 4. libvirt chown's the disk files to root:root for people using
> > qemu:///system. I don't know why it is doing this, but it is likely
> > related to upstream changes (and assumptions) made for the DAC security
> > driver. This seems like someone will need to at least investigate if not
> > patch.
> Hmm, okay, I think this is okay.  Looking at
> /var/lib/eucalyptus/instances/admin/*/disk, these are owned by
> root:root right now with libvirt 0.7.5-5ubuntu15 and eucalyptus
> 1.6.2-0ubuntu26, which is working.

Could this be related to apparmor ? As I found in (but I guess
I ddin't comment there).  If you chown root:root the qemu source and qemu
backing device of a qcow image it will work.  If either is user-owned, it
will not.

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