network: add support for HSR netdev

Add support for creating HSR/PRP interfaces. HSR (High-availability Seamless
Redundancy) and PRP (Parallel Redundancy Protocol) are two protocols that
provide seamless failover against failure of any single network component. They
are both implemented by the "hsr" kernel driver.

test/test-network/conf/25-hsr.netdev

@@ -0,0 +1,7 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[NetDev]
+Name=hsr99
+Kind=hsr
+
+[HSR]
+Ports=test1 dummy98

test/test-network/conf/25-hsr.network

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+[Match]
+Name=hsr99
+
+[Network]
+IPv6AcceptRA=no

test/test-network/systemd-networkd-tests.py

@@ -2057,6 +2057,39 @@ class NetworkdNetDevTests(unittest.TestCase, Utilities):
                 networkctl_reload()
                 self.wait_online('ipvlan99:degraded', 'test1:degraded')
 
+    @expectedFailureIfModuleIsNotAvailable('hsr')
+    def test_hsr(self):
+        first = True
+        for proto, supervision in [['hsr', 9], ['prp', 127]]:
+            if first:
+                first = False
+            else:
+                self.tearDown()
+
+            print(f'### test_hsr(proto={proto}, supervision={supervision})')
+            with self.subTest(proto=proto, supervision=supervision):
+                copy_network_unit('25-hsr.netdev', '25-hsr.network',
+                                  '11-dummy.netdev', '11-dummy.network',
+                                  '12-dummy.netdev', '12-dummy-no-address.network')
+                with open(os.path.join(network_unit_dir, '25-hsr.netdev'), mode='a', encoding='utf-8') as f:
+                    f.write('Protocol=' + proto + '\nSupervision=' + str(supervision))
+
+                start_networkd()
+                self.wait_online('hsr99:degraded')
+                self.networkctl_check_unit('hsr99', '25-hsr', '25-hsr')
+                self.networkctl_check_unit('test1', '11-dummy', '11-dummy')
+                self.networkctl_check_unit('dummy98', '12-dummy', '12-dummy-no-address')
+
+                output = check_output('ip -d link show hsr99')
+                print(output)
+                self.assertRegex(output, 'hsr slave1 test1 slave2 dummy98')
+                self.assertRegex(output, f'supervision 01:15:4e:00:01:{supervision:02x}')
+                self.assertRegex(output, 'proto ' + ('0' if proto == 'hsr' else '1') + ' ')
+
+                touch_network_unit('25-hsr.netdev')
+                networkctl_reload()
+                self.wait_online('hsr99:degraded')
+
     @expectedFailureIfModuleIsNotAvailable('ipvtap')
     def test_ipvtap(self):
         first = True