Re: [Qemu-devel] [PATCH] block: Set cdrom device read only flag

[Kevin Shanahan]

On Thu, Aug 02, 2012 at 11:46:13AM +0930, Kevin Shanahan wrote:
> On Thu, Aug 02, 2012 at 11:02:42AM +0930, Kevin Shanahan wrote:
> > Set the block driver read_only flag for cdrom devices so that
> > qmp_change_blockdev does not attempt to open cdrom files in read-write
> > mode when changing media.
> 
> Hrm, this fixes my simple test case using the kvm monitor directly but
> changing media via libvirt still has the same issue (fails for RO
> files, succeeds for writable files).
> 
> $ virsh attach-disk --type cdrom --mode readonly test1 
> /srv/kvm/iso/ubuntu-12.04-server-amd64.iso hdc
> error: Failed to attach disk
> error: internal error unable to execute QEMU command 'change': Could not open 
> '/srv/kvm/iso/ubuntu-12.04-server-amd64.iso'
> 
> I'll keep looking into it.

In the libvirt case, it seems libvirt is failing to add media=cdrom to
the commandline, so in this case qemu is defaulting to media=disk and
my proposed fix has no effect. Diving into libvirt now to see why no
media=disk is getting added...

Common test case has this xml (generated by virt-install):

    <disk type='block' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <alias name='ide0-1-0'/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>

> Cheers,
> Kevin.