storage: add Pool.import_data to the API

Allow importing not only from another volume, but also raw data. In
practice, for all currently implemented storage pools, this is the same
as Pool.export, because path returned there is read-write. But lets not
abuse this fact, some future implementation may need different methods.

QubesOS/qubes-issues#2622
QubesOS/qubes-issues#2256

qubes/storage/__init__.py

@@ -544,6 +544,15 @@ class Storage(object):
 
         return self.pools[volume].export(self.vm.volumes[volume])
 
+    def import_data(self, volume):
+        ''' Helper function to import volume data (pool.import_data(volume))'''
+        assert isinstance(volume, (Volume, str)), \
+            "You need to pass a Volume or pool name as str"
+        if isinstance(volume, Volume):
+            return self.pools[volume.name].import_data(volume)
+
+        return self.pools[volume].import_data(self.vm.volumes[volume])
+
 
 class Pool(object):
     ''' A Pool is used to manage different kind of volumes (File
@@ -614,6 +623,15 @@ class Pool(object):
         ''' Returns an object that can be `open()`. '''
         raise self._not_implemented("export")
 
+    def import_data(self, volume):
+        ''' Returns an object that can be `open()`.
+
+        Storage implementation may register for
+        `domain-volume-import-end` event to cleanup after this. The
+        event will have also success=True|False information.
+        '''
+        raise self._not_implemented("import")
+
     def import_volume(self, dst_pool, dst_volume, src_pool, src_volume):
         ''' Imports data to a volume in this pool '''
         raise self._not_implemented("import_volume")

qubes/storage/file.py

@@ -198,6 +198,9 @@ class FilePool(qubes.storage.Pool):
     def export(self, volume):
         return volume.path
 
+    def import_data(self, volume):
+        return volume.path
+
     def reset(self, volume):
         ''' Remove and recreate a volatile volume '''
         assert volume._is_volatile, "Not a volatile volume"

qubes/storage/lvm.py

@@ -114,10 +114,11 @@ class ThinPool(qubes.storage.Pool):
     def export(self, volume):
         ''' Returns an object that can be `open()`. '''
         devpath = '/dev/' + volume.vid
-        if not os.access(devpath, os.R_OK):
+        return devpath
-            # FIXME: convert to udev rules, and drop after introducing qubesd
+
-            subprocess.check_call(['sudo', 'chgrp', 'qubes', devpath])
+    def import_data(self, volume):
-            subprocess.check_call(['sudo', 'chmod', 'g+rw', devpath])
+        ''' Returns an object that can be `open()`. '''
+        devpath = '/dev/' + volume.vid
         return devpath
 
     def init_volume(self, vm, volume_config):