[libvirt] [frankschreuder at outlook.com: Fwd: Reproducible live disk detach bug]

[Frank Schreuder]

Hi Laine,

I'm sorry for starting 3 threads with the same topic, seems like my mail 
was heavily delayed yesterday.

[ removing personal mail ]

Op 8/7/2015 om 12:24 AM schreef Laine Stump:
>>> Subject: Reproducible live disk detach bug
>>>
>>> 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?
> I can't tell you right off why the failure message is there, but the
> alias with the added "drive-" is easily explained.
>
> Each <disk> element in the libvirt config corresponds to two entities in
> the qemu virtual machine - a "device" component (what is seen by the
> guest) and a "drive" component (what resources are used on the host to
> back up that device). Each of these corresponds to a separate qemu
> commandline argument (named "-device" and "-drive"), and each of those
> must have a different, unique "id" option. For example, this is what is
> added to my qemu commandline when I add a virtio disk named
> "rawhide.qcow2" to my virtual machine:
>
> -drive
> file=/var/lib/libvirt/images/rawhide.qcow2,if=none,id=drive-virtio-disk0,format=qcow2
> -device
> virtio-blk-pci,scsi=off,bus=pci.2,addr=0x5,drive=drive-virtio-disk0,id=virtio-disk0,bootindex=1
>
>
> If you look at the status XML of the domain while it is running, you'll
> see that the <alias> for the disk element is "virtio-disk0", and that's
> what is given to the -device half of the disk as its qemu id. The -drive
> half uses "drive-$alias" as its qemu id though (you'll notice that the
> -device half references that id with its "drive" option - that's how the
> two halves are tied together by qemu).
>
> So, there is nothing unusual about qemu wanting to delete something
> called drive-virtio-disk4 when you have a <disk> with
> alias='virtio-disk4'. It obviously isn't right that an error message is
> being logged. Something sounds familiar about the "missing device in
> device deleted event" message, but I can't recall details. Does anyone
> else have a better memory? Frank - would it be possible for you to try
> this same sequence of events with the same libvirt and an older qemu
> (and/or vice-versa)?
>

I have some more interesting debug information.

I'm -not- able to reproduce it on libvirt 1.2.11 - qemu 2.3.0 and 
libvirt 1.2.11 - qemu 1.7.1 using a FreeBSD VM.
I'm able to reproduce the errors with libvirt 1.2.11 - qemu 2.3.0 and 
libvirt 1.2.18 - qemu 2.3.0 using a Debian VM.
Seems like the error triggers depending on the guest OS?

During hot-unplugging of network interfaces libvirt also triggers the 
same error on a Debian VM:

2015-08-06 10:48:59.945+0000: 11662: error : qemuMonitorJSONHandleDeviceDeleted:939 : missing device in device deleted event


I gathered some logging information with info level logging enabled 
while detaching a disk:
http://pastebin.com/raw.php?i=vVLuavG2

Debug level logging output was too big for a pastebin, contact me if you 
are interested in the debug level output logging.

Hope this will help solving this issue, if there is more information I 
can provide or tests I can execute, please let me know.

Thanks,
Frank