networkd: support socket activation

Still keep the non-socket activation code around for starting from the commandline, but
will likely drop that too in the future.

Makefile.am

@@ -5668,9 +5668,11 @@ tests += \
 
 nodist_systemunit_DATA += \
 	units/systemd-networkd.service \
+	units/systemd-networkd.socket \
 	units/systemd-networkd-wait-online.service
 
 GENERAL_ALIASES += \
+	$(systemunitdir)/systemd-networkd.socket $(pkgsysconfdir)/system/sockets.target.wants/systemd-networkd.socket \
 	$(systemunitdir)/systemd-networkd.service $(pkgsysconfdir)/system/multi-user.target.wants/systemd-networkd.service \
 	$(systemunitdir)/systemd-networkd-wait-online.service $(pkgsysconfdir)/system/network-online.target.wants/systemd-networkd-wait-online.service
 

src/libsystemd/sd-rtnl/sd-rtnl.c

@@ -74,7 +74,7 @@ int sd_rtnl_new_from_netlink(sd_rtnl **ret, int fd) {
 
         assert_return(ret, -EINVAL);
 
-        r = sd_rtnl_new(ret);
+        r = sd_rtnl_new(&rtnl);
         if (r < 0)
                 return r;
 

src/network/networkd-manager.c

@@ -35,6 +35,7 @@
 #include "virt.h"
 
 #include "sd-rtnl.h"
+#include "sd-daemon.h"
 
 /* use 8 MB for receive socket kernel queue. */
 #define RCVBUF_SIZE    (8*1024*1024)
@@ -75,9 +76,33 @@ static int setup_default_address_pool(Manager *m) {
         return 0;
 }
 
+static int systemd_netlink_fd(int *ret) {
+        int n, fd, rtnl_fd = -1;
+
+        n = sd_listen_fds(true);
+        if (n <= 0)
+                return -EINVAL;
+
+        for (fd = SD_LISTEN_FDS_START; fd < SD_LISTEN_FDS_START + n; fd ++) {
+                if (sd_is_socket(fd, AF_NETLINK, SOCK_RAW, -1) > 0) {
+                        if (rtnl_fd >= 0)
+                                return -EINVAL;
+
+                        rtnl_fd = fd;
+                }
+        }
+
+        if (rtnl_fd < 0)
+                return -EINVAL;
+
+        *ret = rtnl_fd;
+
+        return 0;
+}
+
 int manager_new(Manager **ret) {
         _cleanup_manager_free_ Manager *m = NULL;
-        int r;
+        int r, fd;
 
         m = new0(Manager, 1);
         if (!m)
@@ -96,14 +121,20 @@ int manager_new(Manager **ret) {
         sd_event_add_signal(m->event, NULL, SIGTERM, NULL, NULL);
         sd_event_add_signal(m->event, NULL, SIGINT, NULL, NULL);
 
-        r = sd_rtnl_open(&m->rtnl, 3, RTNLGRP_LINK, RTNLGRP_IPV4_IFADDR,
-                         RTNLGRP_IPV6_IFADDR);
-        if (r < 0)
-                return r;
+        if (systemd_netlink_fd(&fd) < 0) {
+                r = sd_rtnl_open(&m->rtnl, 3, RTNLGRP_LINK, RTNLGRP_IPV4_IFADDR,
+                                 RTNLGRP_IPV6_IFADDR);
+                if (r < 0)
+                        return r;
 
-        r = sd_rtnl_inc_rcvbuf(m->rtnl, RCVBUF_SIZE);
-        if (r < 0)
-                return r;
+                r = sd_rtnl_inc_rcvbuf(m->rtnl, RCVBUF_SIZE);
+                if (r < 0)
+                        return r;
+        } else {
+                r = sd_rtnl_new_from_netlink(&m->rtnl, fd);
+                if (r < 0)
+                        return r;
+        }
 
         r = sd_bus_default_system(&m->bus);
         if (r < 0 && r != -ENOENT) /* TODO: drop when we can rely on kdbus */

units/systemd-networkd.service.in

@@ -29,3 +29,4 @@ WatchdogSec=1min
 
 [Install]
 WantedBy=multi-user.target
+Also=systemd-networkd.socket

units/systemd-networkd.socket

@@ -0,0 +1,20 @@
+#  This file is part of systemd.
+#
+#  systemd is free software; you can redistribute it and/or modify it
+#  under the terms of the GNU Lesser General Public License as published by
+#  the Free Software Foundation; either version 2.1 of the License, or
+#  (at your option) any later version.
+
+[Unit]
+Description=networkd rtnetlink socket
+Documentation=man:systemd-networkd.service(8) man:rtnetlink(7)
+DefaultDependencies=no
+Before=sockets.target
+
+[Socket]
+ReceiveBuffer=8M
+ListenNetlink=route 273
+PassCredentials=yes
+
+[Install]
+WantedBy=sockets.target