Fix the LV NotFound situation for thin-type LVM

If the logical volume is not found, LVM displays on the error output
that the volumes could not be found. So here, we filter on this very
specific situation, and let all the other cases go through the stack.

Added a test for this new code path, which raises an exception of the
proper type to be caught by the new code.

Change-Id: I703af8ccd87c6332d9f88eff63fcf26ebed234f4
Closes-Bug: #1390081

cinder/brick/local_dev/lvm.py

@@ -25,9 +25,12 @@ import time
 from cinder.brick import exception
 from cinder.brick import executor
 from cinder.i18n import _
+from cinder.openstack.common import excutils
+from cinder.openstack.common.gettextutils import _LW
 from cinder.openstack.common import log as logging
 from cinder.openstack.common import processutils as putils
 
+
 LOG = logging.getLogger(__name__)
 
 
@@ -284,10 +287,22 @@ class LVM(executor.Executor):
         :returns: dict representation of Logical Volume if exists
 
         """
-        ref_list = self.get_volumes(name)
-        for r in ref_list:
-            if r['name'] == name:
-                return r
+        try:
+            ref_list = self.get_volumes(name)
+            for r in ref_list:
+                if r['name'] == name:
+                    return r
+        except putils.ProcessExecutionError as err:
+            # NOTE(joachim): Catch the "notfound" case from the stderr
+            # in order to let the other errors through.
+            with excutils.save_and_reraise_exception(reraise=True) as ctx:
+                if "not found" in err.stderr:
+                    ctx.reraise = False
+                    LOG.warning(
+                        _LW("Caught exception for lvs 'LV not found': %s")
+                        % (name)
+                    )
+        return None
 
     @staticmethod
     def get_all_physical_volumes(root_helper, vg_name=None):

cinder/tests/brick/test_brick_lvm.py

@@ -89,6 +89,10 @@ class BrickLvmTestCase(test.TestCase):
                     "mXzbuX-dKpG-Rz7E-xtKY-jeju-QsYU-SLG8Z3\n"
         elif ('env, LC_ALL=C, lvs, --noheadings, '
               '--unit=g, -o, vg_name,name,size' in cmd_string):
+            if 'fake-unknown' in cmd_string:
+                raise processutils.ProcessExecutionError(
+                    stderr="One of more volume(s) not found."
+                )
             data = "  fake-vg fake-1 1.00g\n"
             data += "  fake-vg fake-2 1.00g\n"
         elif ('env, LC_ALL=C, lvdisplay, --noheading, -C, -o, Attr' in
@@ -147,6 +151,9 @@ class BrickLvmTestCase(test.TestCase):
     def test_get_volume(self):
         self.assertEqual(self.vg.get_volume('fake-1')['name'], 'fake-1')
 
+    def test_get_volume_none(self):
+        self.assertEqual(self.vg.get_volume('fake-unknown'), None)
+
     def test_get_all_physical_volumes(self):
         # Filtered VG version
         pvs = self.vg.get_all_physical_volumes('sudo', 'fake-vg')