[PATCH][1] xend: avoid tapdisk2 not exit for tap-ctl list failed

[yili <yilikernel@gmail.com>]

Process a is closing tapdisk2 for vm1.
Process b is starting to close vm2.
Process b maybe cannot get the tapdisk info of vm2 using tap-ctl list.
Signed-off-by: Yi Li <peteryili@tencent.com>
---
 tools/python/xen/xend/server/BlktapController.py | 31 ++++++++++++++++++++----
 1 file changed, 26 insertions(+), 5 deletions(-)

diff --git a/tools/python/xen/xend/server/BlktapController.py b/tools/python/xen/xend/server/BlktapController.py
index 60079eb..0bff247 100644
--- a/tools/python/xen/xend/server/BlktapController.py
+++ b/tools/python/xen/xend/server/BlktapController.py
@@ -206,6 +206,8 @@ class TapdiskController(object):
 
     TAP_CTL = 'tap-ctl'
     TAP_DEV = '/dev/xen/blktap-2/tapdev'
+    TAPDISK_SYSFS   = '/sys/class/blktap2'
+    TAPDISK_CONTROL = TAPDISK_SYSFS + '/blktap'
 
     class Tapdisk(object):
         def __init__(self, pid=None, minor=-1, state=None,
@@ -274,11 +276,30 @@ class TapdiskController(object):
     @staticmethod
     def fromDevice(device):
         if device.startswith(TapdiskController.TAP_DEV):
-            minor = os.minor(os.stat(device).st_rdev)
-            tapdisks = filter(lambda x: x.minor == minor,
-                              TapdiskController.list())
-            if len(tapdisks) == 1:
-                return tapdisks[0]
+            tapdisk = TapdiskController.Tapdisk()
+            pattern = re.compile(TapdiskController.TAP_DEV + '(\d+)$')
+            groups  = pattern.search(device)
+            if not groups:
+                raise Exception, 'malformed tap device: ' + device
+            minor   = groups.group(1)
+            control = TapdiskController.TAPDISK_CONTROL + minor
+
+            tapdisk.minor = int(minor)
+            if tapdisk.minor >= 0:
+                tapdisk.device = '%s%s' % \
+                    (TapdiskController.TAP_DEV, tapdisk.minor)
+
+            pid_file = open(control + '/task')
+            tapdisk.pid = int(pid_file.readline())
+            pid_file.close()
+
+            args_file = open(control + '/name')
+            value = args_file.readline()
+            args_file.close()
+            if value.find(':') != -1:
+                tapdisk.dtype, tapdisk.image = value.split(':', 1)
+
+            return tapdisk
         return None
 
     @staticmethod
-- 
1.7.12.4