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

["James (song wei)" <jsong@novell.com>]

Blktapctl thread will use qemu-dm connection instead of tapdisk-ioemu in the
case of FV VM. We found the resource like memory allocated for this Guest
can't be free for backend driver couldn't be closed in qemu-dm. 
This patch would  remove the backend of tapdisk device earlier in xenstore
to triger qemu-dm to notify the backend driver to release the resource
allocated.
I have tested this patch at the case of
1, save && restore 
2, destory && shutdown
3, snapshot

regards,

-James (Song Wei)



Signed-off-by: James ( Song Wei ) <jsong@novell.com> 
diff -r fadf63ab49e7 tools/python/xen/xend/XendDomainInfo.py
--- 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);
                                                                  
http://old.nabble.com/file/p28325456/tapdisk-close.patch tapdisk-close.patch 
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