Add default_qrexec_timeout to qubes-prefs

When a VM (or its template) does not explicitly set a qrexec_timeout,
fall back to a global default_qrexec_timeout (with default value 60),
instead of hardcoding the fallback value to 60.

This makes it easy to set a higher timeout for the whole system, which
helps users who habitually launch applications from several (not yet
started) VMs at the same time. 60 seconds can be too short for that.

qubes/app.py

@@ -718,6 +718,13 @@ class Qubes(qubes.PropertyHolder):
         setter=_setter_pool,
         doc='Default storage pool for kernel volumes')
 
+    default_qrexec_timeout = qubes.property('default_qrexec_timeout',
+        load_stage=3,
+        default=60,
+        type=int,
+        doc='''Default time in seconds after which qrexec connection attempt is
+            deemed failed''')
+
     stats_interval = qubes.property('stats_interval',
         default=3,
         type=int,

qubes/tests/vm/__init__.py

@@ -88,6 +88,7 @@ class TestApp(qubes.tests.TestEmitter):
         self.default_pool_root = 'default'
         self.default_pool_private = 'default'
         self.default_pool_kernel = 'linux-kernel'
+        self.default_qrexec_timeout = 60
         self.default_netvm = None
         self.domains = TestVMsCollection()
         #: jinja2 environment for libvirt XML templates

qubes/tests/vm/qubesvm.py

@@ -459,6 +459,15 @@ class TC_90_QubesVM(QubesVMTestsMixin, qubes.tests.QubesTestCase):
         self.assertPropertyInvalidValue(vm, 'qrexec_timeout', '-2')
         self.assertPropertyInvalidValue(vm, 'qrexec_timeout', '')
 
+    def test_272_qrexec_timeout_global_changed(self):
+        self.app.default_qrexec_timeout = 123
+        vm = self.get_vm()
+        self.assertPropertyDefaultValue(vm, 'qrexec_timeout', 123)
+        self.assertPropertyValue(vm, 'qrexec_timeout', 3, 3, '3')
+        del vm.qrexec_timeout
+        self.assertPropertyDefaultValue(vm, 'qrexec_timeout', 123)
+        self.assertPropertyValue(vm, 'qrexec_timeout', '3', 3, '3')
+
     def test_280_autostart(self):
         vm = self.get_vm()
         # FIXME any better idea to not involve systemctl call at this stage?

qubes/vm/qubesvm.py

@@ -510,7 +510,8 @@ class QubesVM(qubes.vm.mix.net.NetVMMixin, qubes.vm.BaseVM):
 #           return self._default_user
 
     qrexec_timeout = qubes.property('qrexec_timeout', type=int,
-        default=_default_with_template('qrexec_timeout', 60),
+        default=_default_with_template('qrexec_timeout',
+            lambda self: self.app.default_qrexec_timeout),
         setter=_setter_positive_int,
         doc='''Time in seconds after which qrexec connection attempt is deemed
             failed. Operating system inside VM should be able to boot in this