On 03/18/2013 08:13 AM, Osier Yang wrote:
I added a disk to virtio-scsi bus through the VM's XML file like this: <disk type='block' device='disk'> <driver name='qemu' type='raw' io='threads'/> <source dev='/mnt/test.raw'/> <target dev='sdb' bus='scsi'/> <shareable/> </disk>
Then when I started the VM, I met the error. [root@build SOURCES]# virsh start pan64ga error: Failed to start domain pan64ga error: Unable to get minor number of device '/mnt/test.raw': Invalid argument
It's not reasonable. As the disk source you use is /mnt/test.raw, I believe it's not a block device. However, you used disk type='block'. Libvirt honors what you specified, and tries to grab the device IDs of the disk source (it expects the disk source is block, but it's not).
This inspires me thinking of we should validate the disk source type somewhere (when parsing or in the driver, as it's general for all drivers).
Any opinions on should we validate whether the disk type and the specified source matches?
Just realized that validating when parsing doesn't make sense, because the validation can imply the checking of whether the disk source existing or not, however, for a inactive domain, it's normal that its disk source may not existing.
So the only way to do the validation is inside driver. But does it imply we will have regression if doing so? As yuxh said, the guest can actually be started successfully with block disk has a plain file source, not sure if it's expected result of qemu though.
I think we are safe arguing that most users have not mixed type='block' with non-block files. The fact that it previously worked was a bug in our level of validation; since we did not document that it should work, I'm okay if we keep the new behavior of erroring out when a file is not a block device. A nicer error than 'Unable to get minor number of device '/mnt/test.raw':' would be appropriate, but I don't think that we are introducing too much of a regression by rejecting an unusual combination that was never documented to work. Still, just to be safe, I'd like to get DV or danpb's opinion. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org