[libvirt] Reproducible live disk detach bug

[Frank Schreuder]

Hey guys,

I am currently running into a reproducible libvirt bug when I detach a 
disk from a running VM using libvirt 1.2.18 and qemu 2.3.0.

I can attach a disk to a running VM without any problems.
During the attach operation I don't create a disk alias name, which 
results in libvirt generating an unique alias.
Using virsh dumpxml I get the following output(snippet):

<disk type='file' device='disk'>
       <driver name='qemu' type='raw' cache='none'/>
       <source file='/var/local/mnt/test-storage/test-storage.raw'/>
       <backingStore/>
       <target dev='vde' bus='virtio'/>
       <iotune>
         <read_bytes_sec>94371840</read_bytes_sec>
         <write_bytes_sec>31457280</write_bytes_sec>
         <read_iops_sec>1000</read_iops_sec>
         <write_iops_sec>200</write_iops_sec>
       </iotune>
       <alias name='virtio-disk4'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x09' function='0x0'/>
</disk>

As you can see, libvirt generates 'virtio-disk4' as an alias. But as 
soon as I try to detach the disk from the running VM, I will receive the 
following two errors in my libvirt log:

2015-08-06 10:48:59.943+0000: 11657: warning : 
qemuMonitorJSONHandleDeviceDeleted:939 : missing device in device 
deleted event
2015-08-06 10:48:59.945+0000: 11662: error : 
qemuMonitorTextDriveDel:2594 : operation failed: deleting 
drive-virtio-disk4 drive failed: 2015-08-06T10:48:59.945058Z Device 
'drive-virtio-disk4' not found

Apparently libvirt tries to detach the disk with a drive- prefix, which 
doesn't exist? The drive seems to detach correctly though.

I hope somebody with more extensive knowledge about libvirt can help me 
solve this issue. If more information is needed, feel free to contact me.

Thanks,
Frank