Detect when HVM guest ejects CDs
This is really a bug for upstream, but tracking it here seems like a good idea.
When an HVM finishes installing an OS or something, it typically tries to eject the CD in the CDROM drive. Xen/qemu-dm doesn't seem to detect this, with the result being that it turns around and boots right back into the CD until you actually power the VM off and then back on.
It seems like it shouldn't be too hard to detect ejects in the device driver and use that to trigger detaching the block device.