remus: proper cleanup on checkpoint failure.

While running remus, when an error occurs during checkpointing
(e.g., timeouts on primary, failing to checkpoint network buffer
or disk or even communication failure) the domU is sometimes
left in suspended state on primary. Instead of blindly closing
the checkpoint file handle, attempt to resume the domain before
the close.

Signed-off-by: Shriram Rajagopalan <rshriram@cs.ubc.ca>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/lowlevel/checkpoint/checkpoint.c

@@ -80,6 +80,9 @@ static PyObject* pycheckpoint_close(PyObject* obj, PyObject* args)
 {
   CheckpointObject* self = (CheckpointObject*)obj;
 
+  if (checkpoint_resume(&self->cps) < 0)
+    fprintf(stderr, "%s\n", checkpoint_error(&self->cps));
+
   checkpoint_close(&self->cps);
 
   Py_XDECREF(self->suspend_cb);

tools/python/xen/remus/save.py

@@ -158,9 +158,13 @@ class Saver(object):
             self.checkpointer.open(self.vm.domid)
             self.checkpointer.start(self.fd, self.suspendcb, self.resumecb,
                                     self.checkpointcb, self.interval)
-            self.checkpointer.close()
         except xen.lowlevel.checkpoint.error, e:
             raise CheckpointError(e)
+        finally:
+            try: #errors in checkpoint close are not critical atm.
+                self.checkpointer.close()
+            except:
+                pass
 
     def _resume(self):
         """low-overhead version of XendDomainInfo.resumeDomain"""