udev: add network link configuration tool

This tool applies hardware specific settings to network devices before they
are announced via libudev.

Settings that will probably eventually be supported are MTU, Speed,
DuplexMode, WakeOnLan, MACAddress, MACAddressPolicy (e.g., 'hardware',
'synthetic' or 'random'), Name and NamePolicy (replacing our current
interface naming logic). This patch only introduces support for
Description, as a proof of concept.

Some of these settings may later be overriden by a network management
daemon/script. However, these tools should always listen and wait on libudev
before touching a device (listening on netlink is not enough). This is no
different from how things used to be, as we always supported changing the
network interface name from udev rules, which does not work if someone
has already started using it.

The tool is configured by .link files in /etc/net/links/ (with the usual
overriding logic in /run and /lib). The first (in lexicographical order)
matching .link file is applied to a given device, and all others are ignored.

The .link files contain a [Match] section with (currently) the keys
MACAddress, Driver, Type (see DEVTYPE in udevadm info) and Path (this
matches on the stable device path as exposed as ID_PATH, and not the
unstable DEVPATH). A .link file matches a given device if all of the
specified keys do. Currently the keys are treated as plain strings,
but some limited globbing may later be added to the keys where it
makes sense.

Example:

/etc/net/links/50-wireless.link
[Match]
MACAddress=98:f2:e4:42:c6:92
Path=pci-0000:02:00.0-bcma-0
Type=wlan

[Link]
Description=The wireless link

1 files changed, 96 insertions, 0 deletions

diff --git a/src/udev/udev-builtin-net_link.c b/src/udev/udev-builtin-net_link.c
new file mode 100644
index 0000000000..d7cbe6a016
--- /dev/null
+++ b/src/udev/udev-builtin-net_link.c
@@ -0,0 +1,96 @@
+/*-*- Mode: C; c-basic-offset: 8; indent-tabs-mode: nil -*-*/
+
+/***
+  This file is part of systemd.
+
+  Copyright 2013 Tom Gundersen
+
+  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.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include "link-config.h"
+#include "udev.h"
+#include "log.h"
+
+link_config_ctx *ctx;
+
+static int builtin_net_link(struct udev_device *dev, int argc, char **argv, bool test) {
+        link_config *link;
+        int r;
+
+        if (argc > 1) {
+                log_error("This program takes no arguments.");
+                return EXIT_FAILURE;
+        }
+
+        r = link_config_get(ctx, dev, &link);
+        if (r < 0) {
+                if (r == -ENOENT) {
+                        log_info("No matching link configuration found");
+                        return EXIT_SUCCESS;
+                } else {
+                        log_error("Could not get link config");
+                        return EXIT_FAILURE;
+                }
+        }
+
+        r = link_config_apply(ctx, link, dev);
+        if (r < 0) {
+                log_error("Could not apply link config");
+                return EXIT_FAILURE;
+        }
+
+        return EXIT_SUCCESS;
+}
+
+static int builtin_net_link_init(struct udev *udev) {
+        int r;
+
+        if (ctx)
+                return 0;
+
+        r = link_config_ctx_new(&ctx);
+        if (r < 0)
+                return r;
+
+        r = link_config_load(ctx);
+        if (r < 0)
+                return r;
+
+        log_debug("Created link configuration context");
+        return 0;
+}
+
+static void builtin_net_link_exit(struct udev *udev) {
+        link_config_ctx_free(ctx);
+        log_debug("Unloaded link configuration context");
+}
+
+static bool builtin_net_link_validate(struct udev *udev) {
+        log_debug("Check if link configuration needs reloading");
+        if (!ctx)
+                return false;
+
+        return link_config_should_reload(ctx);
+}
+
+const struct udev_builtin udev_builtin_net_link = {
+        .name = "net_link",
+        .cmd = builtin_net_link,
+        .init = builtin_net_link_init,
+        .exit = builtin_net_link_exit,
+        .validate = builtin_net_link_validate,
+        .help = "configure network link",
+        .run_once = false,
+};