Re: earlier remove the backend of tapdisk device in xenstore to release the resource allocated in backend driver lies in dom0'kernel

[Jim Fehlig <jfehlig@novell.com>]

Jan Beulich wrote:
>>>> "James (song wei)" <jsong@novell.com> 22.04.10 10:08 >>>
>>>>         
>> --- a/tools/python/xen/xend/XendDomainInfo.py   Mon Apr 19 17:57:28 2010 +0100
>> +++ b/tools/python/xen/xend/XendDomainInfo.py   Thu Apr 22 15:54:01 2010 +0800
>> @@ -2406,8 +2406,13 @@
>>
>>     def _releaseDevices(self, suspend = False):
>>         """Release all domain's devices.  Nothrow guarantee."""
>> +        t = xstransact("%s/device" % self.vmpath)
>>         if self.image:
>>             try:
>> +                for dev in t.list('tap'):
>> +                    log.debug("Early removing %s", dev);
>> +                    self.getDeviceController('tap').destroyDevice(dev, True)
>> +                time.sleep(0.1)
>>                 log.debug("Destroying device model")
>>                 self.image.destroyDeviceModel()
>>             except Exception, e:
>> @@ -2416,9 +2421,10 @@
>>             log.debug("No device model")
>>
>>         log.debug("Releasing devices")
>> -        t = xstransact("%s/device" % self.vmpath)
>>         try:
>>             for devclass in XendDevices.valid_devices():
>> +                if devclass is 'tap':
>> +                    continue
>>                 for dev in t.list(devclass):
>>                     try:
>>                         log.debug("Removing %s", dev);
>>     
>                                                                   
> This seems more like a hack than a solution: Surely qemu-dm gets
> sent some sort of signal to shut down and clean up. The question
> thus really is why that cleanup doesn't include cleaning up blktap
> related resources. That is, I would expect the fix to be in qemu-dm,
> or at most in the xend code that reaps qemu-dm.
>   

Agreed.  qemu-dm should clean up these resources on shutdown.  AFAICT,
it currently relies on receiving CTRMSG_CLOSE from blktapctrl (see
ioemu-dir/hw/xen_blktap.c), which it may never receive before exiting.

Regards,
Jim