Execute pygrub using nova-rootwrap in xenapi

Preserve the behavior where, if pygrub fails, compute attempts
to spawn the VM in HVM mode.

Fixes bug #1091628

Change-Id: Ia462964ebb1fc21d8e289de32557a2e7867f1257

etc/nova/rootwrap.d/compute.filters

@@ -92,6 +92,9 @@ iscsiadm: CommandFilter, iscsiadm, root
 # nova/virt/xenapi/vm_utils.py: 'parted', '--script', dev_path, ..*.
 parted: CommandFilter, parted, root
 
+# nova/virt/xenapi/vm_utils.py: 'pygrub', '-qn', dev_path
+pygrub: CommandFilter, /usr/bin/pygrub, root
+
 # nova/virt/xenapi/vm_utils.py: fdisk %(dev_path)s
 fdisk: CommandFilter, /sbin/fdisk, root
 

nova/virt/xenapi/vm_utils.py

@@ -1910,14 +1910,21 @@ def _get_this_vm_ref(session):
 def _is_vdi_pv(dev):
     LOG.debug(_("Running pygrub against %s"), dev)
     dev_path = utils.make_dev_path(dev)
-    output = os.popen('pygrub -qn %s' % dev_path)
-    for line in output.readlines():
-        #try to find kernel string
-        m = re.search('(?<=kernel:)/.*(?:>)', line)
-        if m and m.group(0).find('xen') != -1:
-            LOG.debug(_("Found Xen kernel %s") % m.group(0))
-            return True
-    LOG.debug(_("No Xen kernel found.  Booting HVM."))
+    try:
+        out, err = utils.execute('pygrub', '-qn', dev_path, run_as_root=True)
+        for line in out:
+            # try to find kernel string
+            m = re.search('(?<=kernel:)/.*(?:>)', line)
+            if m and m.group(0).find('xen') != -1:
+                LOG.debug(_("Found Xen kernel %s") % m.group(0))
+                return True
+        LOG.debug(_("No Xen kernel found.  Booting HVM."))
+    except exception.ProcessExecutionError:
+        LOG.exception(_("Error while executing pygrub! Please, ensure the "
+                        "binary is installed correctly, and available in your "
+                        "PATH; on some Linux distros, pygrub may be installed "
+                        "in /usr/lib/xen-X.Y/bin/pygrub. Attempting to boot "
+                        "in HVM mode."))
     return False