ip: add support of netconf messages

Example of the output:
$ ip monitor netconf&
[1] 24901
$ echo 0 > /proc/sys/net/ipv6/conf/all/forwarding
ipv6 dev lo forwarding off
ipv6 dev eth0 forwarding off
ipv6 all forwarding off
$ echo 1 > /proc/sys/net/ipv4/conf/eth0/forwarding
ipv4 dev eth0 forwarding on

$ ip -6 netconf
ipv6 all forwarding on mc_forwarding 0
$ ip netconf show dev eth0
ipv4 dev eth0 forwarding on rp_filter off mc_forwarding 1
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>

Minor cleanup of original patch, made sure netconf.h matched
result of santized kernel headers

include/linux/netconf.h

+#ifndef _LINUX_NETCONF_H_
+#define _LINUX_NETCONF_H_
+
+#include <linux/types.h>
+#include <linux/netlink.h>
+
+struct netconfmsg {
+	__u8	ncm_family;
+};
+
+enum {
+	NETCONFA_UNSPEC,
+	NETCONFA_IFINDEX,
+	NETCONFA_FORWARDING,
+	NETCONFA_RP_FILTER,
+	NETCONFA_MC_FORWARDING,
+	__NETCONFA_MAX
+};
+#define NETCONFA_MAX	(__NETCONFA_MAX - 1)
+
+#define NETCONFA_IFINDEX_ALL		-1
+#define NETCONFA_IFINDEX_DEFAULT	-2
+
+#endif /* _LINUX_NETCONF_H_ */

ip/ipnetconf.c

+/*
+ * ipnetconf.c		"ip netconf".
+ *
+ *		This program is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Authors:	Nicolas Dichtel, <nicolas.dichtel@6wind.com>
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <syslog.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/time.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+
+#include "rt_names.h"
+#include "utils.h"
+#include "ip_common.h"
+
+static struct
+{
+	int family;
+	int ifindex;
+} filter;
+
+static void usage(void) __attribute__((noreturn));
+
+static void usage(void)
+{
+	fprintf(stderr, "Usage: ip netconf show [ dev STRING ]\n");
+	exit(-1);
+}
+
+#define NETCONF_RTA(r)	((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct netconfmsg))))
+
+int print_netconf(const struct sockaddr_nl *who, struct nlmsghdr *n, void *arg)
+{
+	FILE *fp = (FILE*)arg;
+	struct netconfmsg *ncm = NLMSG_DATA(n);
+	int len = n->nlmsg_len;
+	struct rtattr *tb[NETCONFA_MAX+1];
+
+	if (n->nlmsg_type == NLMSG_ERROR)
+		return -1;
+	if (n->nlmsg_type != RTM_NEWNETCONF) {
+		fprintf(stderr, "Not RTM_NEWNETCONF: %08x %08x %08x\n",
+			n->nlmsg_len, n->nlmsg_type, n->nlmsg_flags);
+
+		return -1;
+	}
+	len -= NLMSG_SPACE(sizeof(*ncm));
+	if (len < 0) {
+		fprintf(stderr, "BUG: wrong nlmsg len %d\n", len);
+		return -1;
+	}
+
+	if (filter.family && filter.family != ncm->ncm_family)
+		return 0;
+
+	parse_rtattr(tb, NETCONFA_MAX, NETCONF_RTA(ncm),
+		     NLMSG_PAYLOAD(n, sizeof(*ncm)));
+
+	switch (ncm->ncm_family) {
+	case AF_INET:
+		fprintf(fp, "ipv4 ");
+		break;
+	case AF_INET6:
+		fprintf(fp, "ipv6 ");
+		break;
+	default:
+		fprintf(fp, "unknown ");
+		break;
+	}
+
+	if (tb[NETCONFA_IFINDEX]) {
+		int *ifindex = (int *)RTA_DATA(tb[NETCONFA_IFINDEX]);
+
+		switch (*ifindex) {
+		case NETCONFA_IFINDEX_ALL:
+			fprintf(fp, "all ");
+			break;
+		case NETCONFA_IFINDEX_DEFAULT:
+			fprintf(fp, "default ");
+			break;
+		default:
+			fprintf(fp, "dev %s ", ll_index_to_name(*ifindex));
+			break;
+		}
+	}
+
+	if (tb[NETCONFA_FORWARDING])
+		fprintf(fp, "forwarding %s ",
+			*(int *)RTA_DATA(tb[NETCONFA_FORWARDING])?"on":"off");
+	if (tb[NETCONFA_RP_FILTER]) {
+		int rp_filter = *(int *)RTA_DATA(tb[NETCONFA_RP_FILTER]);
+
+		if (rp_filter == 0)
+			fprintf(fp, "rp_filter off ");
+		else if (rp_filter == 1)
+			fprintf(fp, "rp_filter strict ");
+		else if (rp_filter == 2)
+			fprintf(fp, "rp_filter loose ");
+		else
+			fprintf(fp, "rp_filter unknown mode ");
+	}
+	if (tb[NETCONFA_MC_FORWARDING])
+		fprintf(fp, "mc_forwarding %d ",
+			*(int *)RTA_DATA(tb[NETCONFA_MC_FORWARDING]));
+
+	fprintf(fp, "\n");
+	fflush(fp);
+	return 0;
+}
+
+void ipnetconf_reset_filter(void)
+{
+	memset(&filter, 0, sizeof(filter));
+}
+
+int do_show(int argc, char **argv)
+{
+	struct {
+		struct nlmsghdr		n;
+		struct netconfmsg	ncm;
+		char			buf[1024];
+	} req;
+
+	ipnetconf_reset_filter();
+	filter.family = preferred_family;
+	if (filter.family == AF_UNSPEC)
+		filter.family = AF_INET;
+	filter.ifindex = NETCONFA_IFINDEX_ALL;
+
+	while (argc > 0) {
+		if (strcmp(*argv, "dev") == 0) {
+			NEXT_ARG();
+			filter.ifindex = ll_name_to_index(*argv);
+			if (filter.ifindex <= 0) {
+				fprintf(stderr, "Device \"%s\" does not exist.\n",
+					*argv);
+				return -1;
+			}
+		}
+		argv++; argc--;
+	}
+
+	ll_init_map(&rth);
+	memset(&req, 0, sizeof(req));
+	req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct netconfmsg));
+	req.n.nlmsg_flags = NLM_F_REQUEST|NLM_F_ACK;
+	req.n.nlmsg_type = RTM_GETNETCONF;
+	req.ncm.ncm_family = filter.family;
+	addattr_l(&req.n, sizeof(req), NETCONFA_IFINDEX, &filter.ifindex,
+		  sizeof(filter.ifindex));
+
+	rtnl_send(&rth, &req.n, req.n.nlmsg_len);
+	rtnl_listen(&rth, print_netconf, stdout);
+
+	return 0;
+}
+
+int do_ipnetconf(int argc, char **argv)
+{
+	if (argc > 0) {
+		if (matches(*argv, "show") == 0 ||
+		    matches(*argv, "lst") == 0 ||
+		    matches(*argv, "list") == 0)
+			return do_show(argc-1, argv+1);
+		if (matches(*argv, "help") == 0)
+			usage();
+	} else
+		return do_show(0, NULL);
+
+	fprintf(stderr, "Command \"%s\" is unknown, try \"ip netconf help\".\n", *argv);
+	exit(-1);
+}