dhcp: Add function for sending a raw packet

Open a packet socket, create a link level header, send packet and
close socket. Adding it to a separate file makes testing of the
DHCP sending much easier, as the test program can supply any socket
to the DHCP client code.

src/libsystemd-dhcp/dhcp-internal.h

@@ -25,6 +25,8 @@
 
 #include "dhcp-protocol.h"
 
+int dhcp_network_send_raw_packet(int index, const void *packet, size_t len);
+
 int dhcp_option_append(uint8_t **buf, size_t *buflen, uint8_t code,
                        size_t optlen, const void *optval);
 

src/libsystemd-dhcp/dhcp-network.c

@@ -0,0 +1,55 @@
+/***
+  This file is part of systemd.
+
+  Copyright (C) 2013 Intel Corporation. All rights reserved.
+
+  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 <errno.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <string.h>
+#include <linux/if_packet.h>
+#include <net/ethernet.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include "socket-util.h"
+
+#include "dhcp-internal.h"
+
+int dhcp_network_send_raw_packet(int index, const void *packet, size_t len)
+{
+        _cleanup_close_ int s;
+        union sockaddr_union link = {};
+
+        s = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC, htons(ETH_P_IP));
+        if (s < 0)
+                return -errno;
+
+        link.ll.sll_family = AF_PACKET;
+        link.ll.sll_protocol = htons(ETH_P_IP);
+        link.ll.sll_ifindex =  index;
+        link.ll.sll_halen = ETH_ALEN;
+        memset(&link.ll.sll_addr, 0xff, ETH_ALEN);
+
+        if (bind(s, &link.sa, sizeof(link.ll)) < 0)
+                return -errno;
+
+        if (sendto(s, packet, len, 0, &link.sa, sizeof(link.ll)) < 0)
+                return -errno;
+
+        return 0;
+}