Use separate QubesVmCollection instance when running a task in background (#986)

QubesVmCollection is not thread safe. If for example update_table() will
be called during some long-running task (like creating or removing VM),
it will try to reload qubes.xml (so get read lock first), but the thread
already holds a lock on this file. This would result in "Lock already
taken" exception.

Fixes qubesos/qubes-issues#986

qubesmanager/create_new_vm.py

@@ -250,39 +250,40 @@ class NewVmDlg (QDialog, Ui_NewVMDlg):
 
         self.done(0)
 
-
-
-    def do_create_vm (self, vmclass, vmname, label, template_vm, netvm, standalone, allow_networking, thread_monitor):
+    @staticmethod
+    def do_create_vm(vmclass, vmname, label, template_vm, netvm,
+                     standalone, allow_networking, thread_monitor):
         vm = None
+        qc = QubesVmCollection()
+        qc.lock_db_for_writing()
+        qc.load()
         try:
-            self.qvm_collection.lock_db_for_writing()
-            self.qvm_collection.load()
-
             if not standalone:
-                vm = self.qvm_collection.add_new_vm(vmclass, name=vmname, template=template_vm, label=label)
+                vm = qc.add_new_vm(vmclass, name=vmname, template=template_vm,
+                                   label=label)
             else:
-                vm = self.qvm_collection.add_new_vm(vmclass, name=vmname, template=None, label=label)
-            vm.create_on_disk(verbose=False, source_template = template_vm)
+                vm = qc.add_new_vm(vmclass, name=vmname, template=None,
+                                   label=label)
+            vm.create_on_disk(verbose=False, source_template=template_vm)
 
-            if allow_networking == False:
+            if not allow_networking:
                 vm.uses_default_netvm = False
                 vm.netvm = None
             else:
                 vm.netvm = netvm
-                if vm.netvm == self.qvm_collection.get_default_netvm():
+                if vm.netvm.qid == qc.get_default_netvm().qid:
                     vm.uses_default_netvm = True
                 else:
                     vm.uses_default_netvm = False
 
-            self.qvm_collection.save()
-
+            qc.save()
         except Exception as ex:
-            thread_monitor.set_error_msg (str(ex))
+            thread_monitor.set_error_msg(str(ex))
             if vm:
                 vm.remove_from_disk()
-                self.qvm_collection.pop(vm.qid)
+                qc.pop(vm.qid)
         finally:
-            self.qvm_collection.unlock_db()
+            qc.unlock_db()
 
         thread_monitor.set_finished()
 

qubesmanager/main.py

@@ -1000,28 +1000,30 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
                                     "ERROR: {0}".format(
                                         thread_monitor.error_msg))
 
-    def do_remove_vm(self, vm, thread_monitor):
+    @staticmethod
+    def do_remove_vm(vm, thread_monitor):
+        qc = QubesVmCollection()
+        qc.lock_db_for_writing()
         try:
-            self.qvm_collection.lock_db_for_writing()
-            self.qvm_collection.load()
-            vm = self.qvm_collection[vm.qid]
+            qc.load()
+            vm = qc[vm.qid]
 
             # TODO: the following two conditions should really be checked
             # by qvm_collection.pop() overload...
             if vm.is_template() and \
-                    self.qvm_collection.default_template_qid == vm.qid:
-                self.qvm_collection.default_template_qid = None
+                    qc.default_template_qid == vm.qid:
+                qc.default_template_qid = None
             if vm.is_netvm() and \
-                    self.qvm_collection.default_netvm_qid == vm.qid:
-                self.qvm_collection.default_netvm_qid = None
+                    qc.default_netvm_qid == vm.qid:
+                qc.default_netvm_qid = None
 
-            self.qvm_collection.pop(vm.qid)
-            self.qvm_collection.save()
+            qc.pop(vm.qid)
+            qc.save()
             vm.remove_from_disk()
         except Exception as ex:
             thread_monitor.set_error_msg(str(ex))
         finally:
-            self.qvm_collection.unlock_db()
+            qc.unlock_db()
 
         thread_monitor.set_finished()
 
@@ -1066,28 +1068,30 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
                                 "Exception while cloning:<br>{0}".format(
                                     thread_monitor.error_msg))
 
-    def do_clone_vm(self, vm, dst_name, thread_monitor):
+    @staticmethod
+    def do_clone_vm(vm, dst_name, thread_monitor):
         dst_vm = None
+        qc = QubesVmCollection()
+        qc.lock_db_for_writing()
+        qc.load()
         try:
-            self.qvm_collection.lock_db_for_writing()
-            self.qvm_collection.load()
-            src_vm = self.qvm_collection[vm.qid]
+            src_vm = qc[vm.qid]
 
-            dst_vm = self.qvm_collection.add_new_vm(src_vm.__class__.__name__,
-                                                    name=dst_name,
-                                                    template=src_vm.template,
-                                                    installed_by_rpm=False)
+            dst_vm = qc.add_new_vm(src_vm.__class__.__name__,
+                                   name=dst_name,
+                                   template=src_vm.template,
+                                   installed_by_rpm=False)
 
             dst_vm.clone_attrs(src_vm)
             dst_vm.clone_disk_files(src_vm=src_vm, verbose=False)
-            self.qvm_collection.save()
-            self.qvm_collection.unlock_db()
+            qc.save()
         except Exception as ex:
             if dst_vm:
-                self.qvm_collection.pop(dst_vm.qid)
+                qc.pop(dst_vm.qid)
                 dst_vm.remove_from_disk()
-            self.qvm_collection.unlock_db()
             thread_monitor.set_error_msg(str(ex))
+        finally:
+            qc.unlock_db()
         thread_monitor.set_finished()
 
     @pyqtSlot(name='on_action_resumevm_triggered')
@@ -1126,8 +1130,8 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
             self.set_error(vm.qid,
                            "Error starting VM: %s" % thread_monitor.error_msg)
 
-    # noinspection PyMethodMayBeStatic
-    def do_start_vm(self, vm, thread_monitor):
+    @staticmethod
+    def do_start_vm(vm, thread_monitor):
         try:
             vm.verify_files()
             vm.start()
@@ -1347,7 +1351,8 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
                                     "ERROR: {0}".format(
                                         thread_monitor.error_msg))
 
-    def do_update_vm(self, vm, thread_monitor):
+    @staticmethod
+    def do_update_vm(vm, thread_monitor):
         try:
             if vm.qid == 0:
                 subprocess.check_call(
@@ -1393,7 +1398,8 @@ class VmManagerWindow(Ui_VmManagerWindow, QMainWindow):
                                 "Exception while running command:<br>{0}".format(
                                     thread_monitor.error_msg))
 
-    def do_run_command_in_vm(self, vm, command_to_run, thread_monitor):
+    @staticmethod
+    def do_run_command_in_vm(vm, command_to_run, thread_monitor):
         try:
             vm.run(command_to_run, verbose=False, autostart=True,
                    notify_function=lambda lvl, msg: trayIcon.showMessage(