networkd: Add bridge port priority setting (#5545)

Allow setting bridge port priority in the Bridge section of the network file,
similar to e.g. port path cost setting.

Set the default to an invalid value of 128, and only set the port priority when
it's not 128. Unlike e.g. path cost, zero is a valid priority value.

Add a networkd-test.py to check that bridge port priority is correctly set.

Incidently, fix bridge port cost type and document valid ranges.

test/networkd-test.py

@@ -96,10 +96,20 @@ class NetworkdTestingUtilities:
         dropin_path = os.path.join(dropin_dir, "%s.conf" % dropin_name)
 
         os.makedirs(dropin_dir, exist_ok=True)
+        self.addCleanup(os.rmdir, dropin_dir)
         with open(dropin_path, 'w') as dropin:
             dropin.write(contents)
         self.addCleanup(os.remove, dropin_path)
 
+    def read_attr(self, link, attribute):
+        """Read a link attributed from the sysfs."""
+        # Note we we don't want to check if interface `link' is managed, we
+        # want to evaluate link variable and pass the value of the link to
+        # assert_link_states e.g. eth0=managed.
+        self.assert_link_states(**{link:'managed'})
+        with open(os.path.join('/sys/class/net', link, attribute)) as f:
+            return f.readline().strip()
+
     def assert_link_states(self, **kwargs):
         """Match networkctl link states to the given ones.
 
@@ -140,6 +150,74 @@ class NetworkdTestingUtilities:
             self.fail("Missing links in status output: %s" % interfaces)
 
 
+class BridgeTest(NetworkdTestingUtilities, unittest.TestCase):
+    """Provide common methods for testing networkd against servers."""
+
+    def setUp(self):
+        self.write_network('port1.netdev', '''\
+[NetDev]
+Name=port1
+Kind=dummy
+MACAddress=12:34:56:78:9a:bc''')
+        self.write_network('port2.netdev', '''\
+[NetDev]
+Name=port2
+Kind=dummy
+MACAddress=12:34:56:78:9a:bd''')
+        self.write_network('mybridge.netdev', '''\
+[NetDev]
+Name=mybridge
+Kind=bridge''')
+        self.write_network('port1.network', '''\
+[Match]
+Name=port1
+[Network]
+Bridge=mybridge''')
+        self.write_network('port2.network', '''\
+[Match]
+Name=port2
+[Network]
+Bridge=mybridge''')
+        self.write_network('mybridge.network', '''\
+[Match]
+Name=mybridge
+[Network]
+DNS=192.168.250.1
+Address=192.168.250.33/24
+Gateway=192.168.250.1''')
+        subprocess.check_call(['systemctl', 'start', 'systemd-networkd'])
+
+    def tearDown(self):
+        subprocess.check_call(['systemctl', 'stop', 'systemd-networkd'])
+        subprocess.check_call(['ip', 'link', 'del', 'mybridge'])
+        subprocess.check_call(['ip', 'link', 'del', 'port1'])
+        subprocess.check_call(['ip', 'link', 'del', 'port2'])
+
+    def test_bridge_init(self):
+        self.assert_link_states(
+            port1='managed',
+            port2='managed',
+            mybridge='managed')
+
+    def test_bridge_port_priority(self):
+        self.assertEqual(self.read_attr('port1', 'brport/priority'), '32')
+        self.write_network_dropin('port1.network', 'priority', '''\
+[Bridge]
+Priority=28
+''')
+        subprocess.check_call(['systemctl', 'restart', 'systemd-networkd'])
+        self.assertEqual(self.read_attr('port1', 'brport/priority'), '28')
+
+    def test_bridge_port_priority_set_zero(self):
+        """It should be possible to set the bridge port priority to 0"""
+        self.assertEqual(self.read_attr('port2', 'brport/priority'), '32')
+        self.write_network_dropin('port2.network', 'priority', '''\
+[Bridge]
+Priority=0
+''')
+        subprocess.check_call(['systemctl', 'restart', 'systemd-networkd'])
+        self.assertEqual(self.read_attr('port2', 'brport/priority'), '0')
+
 class ClientTestBase(NetworkdTestingUtilities):
     """Provide common methods for testing networkd against servers."""