Generate udev rules files to rename devices

Due to a systemd issue[1], using link files to rename interfaces
doesn't work as expected. Link files will not rename an interface
if it was already renamed, and interfaces are renamed in initrd.

However, rules files will cause a renaming, even if the interface
has been renamed in initrd.

So, if we have a driver and/or a mac address and set-name, generate
a udev rules file in /run/udev/rules.d/70-netplan-<interface>.rules

This is at least a temporary fix to LP: #1770082

[1] systemd/systemd#9006

Signed-off-by: Daniel Axtens <dja@axtens.net>

src/networkd.c

@@ -394,6 +394,40 @@ write_network_file(net_definition* def, const char* rootdir, const char* path)
     g_string_free_to_file(s, rootdir, path, ".network");
 }
 
+static void
+write_rules_file(net_definition* def, const char* rootdir)
+{
+    GString* s = NULL;
+    g_autofree char* path = g_strjoin(NULL, "run/udev/rules.d/70-netplan-", def->id, ".rules", NULL);
+
+    /* do we need to write a .rules file?
+     * It's only required for reliably setting the name of a physical device
+     * until systemd issue #9006 is resolved. */
+    if (def->type >= ND_VIRTUAL)
+        return;
+
+    if (!def->set_name || (!def->match.mac && !def->match.driver))
+        return;
+
+    /* build file contents */
+    s = g_string_sized_new(200);
+
+    g_string_append(s, "SUBSYSTEM==\"net\", ACTION==\"add\", ");
+
+    if (def->match.driver) {
+        g_string_append_printf(s,"DRIVERS==\"%s\", ", def->match.driver);
+    } else {
+        g_string_append(s, "DRIVERS==\"?*\", ");
+    }
+
+    if (def->match.mac)
+        g_string_append_printf(s, "ATTR{address}==\"%s\", ", def->match.mac);
+
+    g_string_append_printf(s, "NAME=\"%s\"\n", def->set_name);
+
+    g_string_free_to_file(s, rootdir, path, NULL);
+}
+
 static void
 write_wpa_conf(net_definition* def, const char* rootdir)
 {
@@ -443,9 +477,10 @@ write_networkd_conf(net_definition* def, const char* rootdir)
 {
     g_autofree char* path_base = g_strjoin(NULL, "run/systemd/network/10-netplan-", def->id, NULL);
 
-    /* We want this for all backends when renaming, as *.link files are
+    /* We want this for all backends when renaming, as *.link and *.rules files are
      * evaluated by udev, not networkd itself or NetworkManager. */
     write_link_file(def, rootdir, path_base);
+    write_rules_file(def, rootdir);
 
     if (def->backend != BACKEND_NETWORKD) {
         g_debug("networkd: definition %s is not for us (backend %i)", def->id, def->backend);