qubes/storage: misc fixes for VM-exposed block devices handling

Add 'backenddomain' element when source (not target) domain is not dom0.
Fix XML elemenet name. Actually set volume.domain when listing
VM-exposed devices.

QubesOS/qubes-issues#2256

qubes/storage/__init__.py

@@ -255,9 +255,9 @@ class Storage(object):
         if not rw:
             lxml.etree.SubElement(disk, 'readonly')
 
-        if self.vm.qid != 0:
+        if volume.domain is not None:
             lxml.etree.SubElement(disk, 'backenddomain').set(
-                'name', volume.pool.split('p_')[1])
+                'name', volume.domain.name)
 
         xml_string = lxml.etree.tostring(disk, encoding='utf-8')
         self.vm.libvirt_domain.attachDevice(xml_string)

qubes/storage/domain.py

@@ -86,7 +86,7 @@ class DomainPool(Pool):
 
             devices[name][atr] = value
 
-        return [DomainVolume(n, self.name, **atrs)
+        return [DomainVolume(n, self.vm, self.name, **atrs)
                 for n, atrs in devices.items()]
 
     def clone(self, source, target):
@@ -99,11 +99,12 @@ class DomainPool(Pool):
 class DomainVolume(Volume):
     ''' A volume provided by a block device in an domain '''
 
-    def __init__(self, name, pool, desc, mode, **kwargs):
+    def __init__(self, vm, name, pool, desc, mode, **kwargs):
         rw = (mode == 'w')
 
         super(DomainVolume, self).__init__(desc, pool, vid=name, removable=True,
                                            rw=rw, **kwargs)
+        self.domain = vm
 
     @property
     def revisions(self):

qubes/storage/file.py

@@ -31,6 +31,7 @@ import os.path
 import re
 import subprocess
 
+import qubes.devices
 import qubes.storage
 
 BLKSIZE = 512

templates/libvirt/xen.xml

@@ -81,7 +81,7 @@
                 {% endif %}
 
                 {% if device.domain %}
-                    <domain name="{{ domain }}" />
+                    <backenddomain name="{{ domain }}" />
                 {% endif %}
 
                 {% if device.script %}