bond: T8023: validate member interface min/max MTU

It is impossible to set the bond interface MTU to be larger or lower then the
limits of the underlaying interface MTU. Add proper commit validation and
smoketest.

Author: c-po

smoketest/scripts/cli/test_interfaces_bonding.py

@@ -20,6 +20,7 @@
 from base_interfaces_test import BasicInterfaceTest
 from base_vyostest_shim import VyOSUnitTestSHIM
 
+from vyos.ethtool import Ethtool
 from vyos.ifconfig import Section
 from vyos.ifconfig.interface import Interface
 from vyos.configsession import ConfigSessionError
@@ -334,5 +335,35 @@ def test_bonding_evpn_multihoming(self):
 
             id = int(id) + 1
 
+    def test_bonding_member_mtu(self):
+        # This Smoketest only works on systems running virtio drivers
+        for interface in self._interfaces:
+            for option in self._options.get(interface, []):
+                self.cli_set(self._base_path + [interface] + option.split())
+
+            self.cli_set(self._base_path + [interface, 'mtu', '10000'])
+
+        is_virtio = False
+        for member in self._members:
+            if Ethtool(member).get_driver_name() == 'virtio_net':
+                is_virtio = True
+                break
+
+        if not is_virtio:
+            self.cli_discard()
+            self.skipTest('Test requires virtio NIC drivers')
+
+        # check validate() - MTU of bond higher then virtio max MTU
+        with self.assertRaises(ConfigSessionError):
+            self.cli_commit()
+
+        for interface in self._interfaces:
+            for option in self._options.get(interface, []):
+                self.cli_set(self._base_path + [interface] + option.split())
+
+            self.cli_delete(self._base_path + [interface, 'mtu'])
+
+        self.cli_commit()
+
 if __name__ == '__main__':
     unittest.main(verbosity=2, failfast=VyOSUnitTestSHIM.TestCase.debug_on())

src/conf_mode/interfaces_bonding.py

@@ -248,6 +248,17 @@ def verify(bond):
                         continue
                     raise ConfigError(error_msg + f'it has a "{option_path.replace(".", " ")}" assigned!')
 
+            if mtu := bond.get('mtu'):
+                mtu = int(mtu)
+                max_mtu = int(EthernetIf(interface).get_max_mtu())
+                min_mtu = int(EthernetIf(interface).get_min_mtu())
+                if mtu > max_mtu:
+                    raise ConfigError('Configured MTU is greater then member '\
+                                      f'interface "{interface}" maximum of {max_mtu}!')
+                if mtu < min_mtu:
+                    raise ConfigError('Configured MTU is less then member '\
+                                      f'interface "{interface}" minimum of {min_mtu}!')
+
     if 'primary' in bond:
         if bond['primary'] not in bond['member']['interface']:
             raise ConfigError(f'Primary interface of bond "{bond_name}" must be a member interface')