storage: volume.import_volume now expect create()d volume

This is much more logical for *import*_volume function.

QubesOS/qubes-issues#2256

qubes/storage/__init__.py

@@ -177,7 +177,11 @@ class Volume(object):
 
     def import_volume(self, src_volume):
         ''' Imports data from a different volume (possibly in a different
-        pool '''
+        pool.
+
+        The needs to be create()d first.
+
+        This can be implemented as a coroutine. '''
         # pylint: disable=unused-argument
         raise self._not_implemented("import_volume")
 
@@ -448,16 +452,9 @@ class Storage(object):
         dst_pool = self.vm.app.get_pool(config['pool'])
         dst = dst_pool.init_volume(self.vm, config)
         src_volume = src_vm.volumes[name]
-        src_pool = src_volume.pool
-        if dst_pool == src_pool:
-            msg = "Cloning volume {!s} from vm {!s}"
-            self.vm.log.info(msg.format(src_volume.name, src_vm.name))
-            clone_op_ret = dst_pool.clone(src_volume, dst)
-        else:
-            msg = "Importing volume {!s} from vm {!s}"
-            self.vm.log.info(msg.format(src_volume.name, src_vm.name))
-            clone_op_ret = dst_pool.import_volume(
-                dst_pool, dst, src_pool, src_volume)
+        msg = "Importing volume {!s} from vm {!s}"
+        self.vm.log.info(msg.format(src_volume.name, src_vm.name))
+        clone_op_ret = dst.import_volume(src_volume)
 
         # clone/import functions may be either synchronous or asynchronous
         # in the later case, we need to wait for them to finish

qubes/storage/file.py

@@ -261,6 +261,7 @@ class FileVolume(qubes.storage.Volume):
         msg = msg.format(src_volume, self)
         assert not src_volume.snap_on_start, msg
         if self.save_on_stop:
+            _remove_if_exists(self.path)
             copy_file(src_volume.export(), self.path)
         return self
 

qubes/storage/lvm.py

@@ -310,10 +310,11 @@ class ThinVolume(qubes.storage.Volume):
         # pylint: disable=line-too-long
         if isinstance(src_volume.pool, ThinPool) and \
                 src_volume.pool.thin_pool == self.pool.thin_pool:  # NOQA
+            cmd = ['remove', self.vid]
+            qubes_lvm(cmd, self.log)
             cmd = ['clone', str(src_volume), str(self)]
             qubes_lvm(cmd, self.log)
         else:
-            self.create()
             src_path = src_volume.export()
             cmd = ['sudo', 'dd', 'if=' + src_path, 'of=/dev/' + self.vid,
                 'conv=sparse']