storage/lvm: allow starting a VM even if not all its volumes are active

Normally, VM gets snapshots of its volumes anyway, so it makes little
sense to enforce they are already active. This requires several changes:
1. Including inactive volumes in the size_cache (those will have 0 as
   usage, because inactive do not report usage).
2. Do not check if volume is active in the verify() function.
3. With the above changed, adjust checking for volume existence by
   looking at size_cache instead of /dev/ node existence. For now do
   this in code paths related to VM startup.
4. In the rare case of not using snapshot (or new volatile volume) do
   activate the volume if needed.

Do not deactivate volumes on stop to not lose information about usage.

All that should solve an issue when qubesd (and possibly some VMs) are
started while LVM is still activating volumes. A simpler (and more
reliable) solution would be to order qubesd.service after activating all
(present at boot) volumes, but unfortunately current LVM + systemd
integration doesn't provide anything to set such ordering.

qubes/storage/lvm.py

@@ -221,14 +221,17 @@ def _parse_lvm_cache(lvm_output):
             size, usage_percent = row['lv_size'], row['data_percent']
         except KeyError:
             continue
-        if '' in [pool_name, name, size, usage_percent]:
+        if '' in [pool_name, name, size]:
             continue
         pool_lv, attr, origin = row['pool_lv'], row['lv_attr'], row['origin']
         metadata_size = row['lv_metadata_size']
         metadata_percent = row['metadata_percent']
         name = pool_name + "/" + name
         size = int(size[:-1])  # Remove 'B' suffix
-        usage = int(size / 100 * float(usage_percent))
+        if usage_percent:
+            usage = int(size / 100 * float(usage_percent))
+        else:
+            usage = 0
         if metadata_size:
             metadata_size = int(metadata_size[:-1])
             metadata_usage = int(metadata_size / 100 * float(metadata_percent))
@@ -384,6 +387,18 @@ async def _remove_revisions(self, revisions=None):
             except qubes.storage.StoragePoolException:
                 pass
 
+    async def _activate(self):
+        """
+        Ensure the volume is active.
+
+        :return: None
+        """
+        vol_info = size_cache[self._vid_current]
+        if vol_info['attr'][4] == 'a':
+            return
+        cmd = ["activate", self._vid_current]
+        await qubes_lvm_coro(cmd, self.log)
+
     async def _commit(self, vid_to_commit=None, keep=False):
         '''
         Commit temporary volume into current one. By default
@@ -407,7 +422,7 @@ async def _commit(self, vid_to_commit=None, keep=False):
             vid_to_commit = self._vid_snap
 
         assert self._lock.locked()
-        if not os.path.exists('/dev/' + vid_to_commit):
+        if vid_to_commit not in size_cache:
             # nothing to commit
             return False
 
@@ -453,7 +468,7 @@ async def create(self):
     async def remove(self):
         assert self.vid
         try:
-            if os.path.exists('/dev/' + self._vid_snap):
+            if self._vid_snap in size_cache:
                 cmd = ['remove', self._vid_snap]
                 await qubes_lvm_coro(cmd, self.log)
         except AttributeError:
@@ -558,8 +573,7 @@ async def import_data_end(self, success):
 
     def abort_if_import_in_progress(self):
         try:
-            devpath = '/dev/' + self._vid_import
-            if os.path.exists(devpath):
+            if self._vid_import in size_cache:
                 raise qubes.storage.StoragePoolException(
                     'Import operation in progress on {}'.format(self.vid))
         except AttributeError:  # self._vid_import
@@ -568,7 +582,7 @@ def abort_if_import_in_progress(self):
 
     def is_dirty(self):
         if self.save_on_stop:
-            return os.path.exists('/dev/' + self._vid_snap)
+            return self._vid_snap in size_cache
         return False
 
     def is_outdated(self):
@@ -673,6 +687,8 @@ async def start(self):
             if self.snap_on_start or self.save_on_stop:
                 if not self.save_on_stop or not self.is_dirty():
                     await self._snapshot()
+                else:
+                    await self._activate()
             else:
                 await self._reset()
         finally:
@@ -707,9 +723,6 @@ async def verify(self):
             vid = self._vid_current
         try:
             vol_info = size_cache[vid]
-            if vol_info['attr'][4] != 'a':
-                raise qubes.storage.StoragePoolException(
-                    'volume {} not active'.format(vid))
         except KeyError:
             raise qubes.storage.StoragePoolException(
                 'volume {} missing'.format(vid))