CA-392823: ensure no device mapper conflicts in LVHDSR detach

Within the detach operation checks are made that none of the device
mapper devices for the SR volume group have opern handles. The falls
false if operations on other LVM srs happen to call a device mapper
operation such as `lvs` or `vgs` at the point the check is made as
these operations can result in all of the devices managed by the
device mapper subsystem being accessed as part of the scan. this then
gives a false response for the open file handles check.

Signed-off-by: Mark Syms <mark.syms@cloud.com>

drivers/LVHDSR.py

@@ -51,6 +51,7 @@
 from xmlrpc.client import DateTime
 import glob
 from constants import CBTLOG_TAG
+from fairlock import Fairlock
 DEV_MAPPER_ROOT = os.path.join('/dev/mapper', lvhdutil.VG_PREFIX)
 
 geneology = {}
@@ -601,13 +602,15 @@ def detach(self, uuid):
             if util.extractSRFromDevMapper(fileName) != self.uuid:
                 continue
 
-            #   check if any file has open handles
-            if util.doesFileHaveOpenHandles(fileName):
-                #   if yes, log this and signal failure
-                util.SMlog("LVHDSR.detach: The dev mapper entry %s has open " \
-                           "handles" % fileName)
-                success = False
-                continue
+            with Fairlock('devicemapper'):
+                # check if any file has open handles
+                if util.doesFileHaveOpenHandles(fileName):
+                    # if yes, log this and signal failure
+                    util.SMlog(
+                        f"LVHDSR.detach: The dev mapper entry {fileName} has "
+                        "open handles")
+                    success = False
+                    continue
 
             # Now attempt to remove the dev mapper entry
             if not lvutil.removeDevMapperEntry(fileName, False):

tests/test_LVHDSR.py

@@ -104,7 +104,7 @@ def test_undoAllInflateJournals(
     @mock.patch('LVHDSR.Lock', autospec=True)
     @mock.patch('SR.XenAPI')
     @testlib.with_context
-    def test_attach_success(self,
+    def test_srlifecycle_success(self,
                             context,
                             mock_xenapi,
                             mock_lock,
@@ -196,7 +196,35 @@ def get_vdi_by_uuid(vdi_uuid):
         # Arrange (2)
         sr = self.create_LVHDSR(master=True, command='sr_detach',
                                 sr_uuid=sr_uuid)
+
+        # Arrange for detach
+        self.stubout('LVHDSR.Fairlock')
+        mock_remove_device = self.stubout(
+            'LVHDSR.lvutil.removeDevMapperEntry')
+        mock_glob = self.stubout('glob.glob')
+        mock_vdi_uuid = "72101dbd-bd62-4a14-a03c-afca8cceec86"
+        mock_filepath = os.path.join(
+            '/dev/mapper/', 'VG_XenStorage'
+            f'--{sr_uuid.replace("-", "--")}-'
+            f'{mock_vdi_uuid.replace("-", "--")}')
+        mock_glob.return_value = [mock_filepath]
+        mock_open_handles = self.stubout(
+            'LVHDSR.util.doesFileHaveOpenHandles')
+
+        # Act (Detach)
+        with self.assertRaises(Exception):
+            # Fail the first one with busy handles
+            mock_open_handles.return_value = True
+            sr.detach(sr.uuid)
+
+        # Now succeed
+        mock_open_handles.return_value = False
         sr.detach(sr.uuid)
+
+        # Assert for detach
+        mock_remove_device.assert_called_once_with(mock_filepath, False)
+
+        # Create new SR
         mock_lvm_cache.return_value.checkLV.return_value = True
         sr = self.create_LVHDSR(master=True, command='sr_attach',
                                 sr_uuid=sr_uuid)