net: option to force MAC address prefix

By default, QEMU sets the first NIC's MAC address to 52:54:00:12:34:56,
and increments the last octet for the next ones. When different VMs need
to discuss between each others via the same bridge, that can cause
conflicts.

A new option has been added to set a different prefix, e.g.

  --mac-address-prefix 52:54:00:12:34

Which will assign 52:54:00:12:34:00 to the fist NIC, and increment the
last octet for the next one, etc.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Author: matttbe

virtme/commands/run.py

@@ -123,6 +123,12 @@ def make_parser() -> argparse.ArgumentParser:
         nargs="?",
         help="Enable basic network access: user, bridge(=<br>), loop.",
     )
+    g.add_argument(
+        "--mac-address-prefix",
+        action="store",
+        default=None,
+        help="The MAC address, excluding the last octet, to assign to the NIC interface, e.g. 52:54:00:12:34",
+    )
     g.add_argument(
         "--balloon",
         action="store_true",
@@ -1329,11 +1335,17 @@ def do_script(shellcmd: str, ret_path=None, show_boot_console=False) -> None:
         if video_args:
             qemuargs.extend(video_args)
 
+    def get_mac(index):
+        if args.mac_address_prefix is None:
+            return ""
+        return ",mac=%s:%02d" % (args.mac_address_prefix, index)
+
     if args.net:
         extend_dhcp = False
         index = 0
         for net in args.net:
-            qemuargs.extend(["-device", "%s,netdev=n%d" % (arch.virtio_dev_type("net"), index)])
+            qemuargs.extend(["-device", "%s,netdev=n%d%s" %
+                            (arch.virtio_dev_type("net"), index, get_mac(index))])
             if net == "user":
                 qemuargs.extend(["-netdev", "user,id=n%d" % index])
                 extend_dhcp = True
@@ -1348,7 +1360,8 @@ def do_script(shellcmd: str, ret_path=None, show_boot_console=False) -> None:
                 hubid = index
                 qemuargs.extend(["-netdev", "hubport,id=n%d,hubid=%d" % (index, hubid)])
                 index += 1
-                qemuargs.extend(["-device", "%s,netdev=n%d" % (arch.virtio_dev_type("net"), index)])
+                qemuargs.extend(["-device", "%s,netdev=n%d%s" %
+                                (arch.virtio_dev_type("net"), index, get_mac(index))])
                 qemuargs.extend(["-netdev", "hubport,id=n%d,hubid=%d" % (index, hubid)])
             else:
                 arg_fail("--net: invalid choice: '%s' (choose from user, bridge(=<br>), loop)" % net)

virtme_ng/run.py

@@ -352,6 +352,13 @@ def make_parser():
         help="Enable network access: user, bridge(=<br>), loop",
     )
 
+    parser.add_argument(
+        "--mac-address-prefix",
+        "-M",
+        action="store",
+        help="The MAC address, excluding the last octet, to assign to the NIC interface, e.g. 52:54:00:12:34",
+    )
+
     parser.add_argument(
         "--disk",
         "-D",
@@ -934,6 +941,12 @@ def _get_virtme_network(self, args):
         else:
             self.virtme_param["network"] = ""
 
+    def _get_virtme_mac_address_prefix(self, args):
+        if args.mac_address_prefix is not None:
+            self.virtme_param["mac_address_prefix"] = "--mac-address-prefix " + args.mac_address_prefix
+        else:
+            self.virtme_param["mac_address_prefix"] = ""
+
     def _get_virtme_disk(self, args):
         if args.disk is not None:
             disk_str = ""
@@ -1088,6 +1101,7 @@ def run(self, args):
         self._get_virtme_no_virtme_ng_init(args)
         self._get_virtme_mods(args)
         self._get_virtme_network(args)
+        self._get_virtme_mac_address_prefix(args)
         self._get_virtme_disk(args)
         self._get_virtme_sound(args)
         self._get_virtme_disable_microvm(args)
@@ -1126,6 +1140,7 @@ def run(self, args):
             + f'{self.virtme_param["no_virtme_ng_init"]} '
             + f'{self.virtme_param["mods"]} '
             + f'{self.virtme_param["network"]} '
+            + f'{self.virtme_param["mac_address_prefix"]} '
             + f'{self.virtme_param["disk"]} '
             + f'{self.virtme_param["sound"]} '
             + f'{self.virtme_param["disable_microvm"]} '