Add bridge command

New tool to allow manipulating forwarding entries and monitoring
bridge events.
diff --git a/bridge/monitor.c b/bridge/monitor.c
new file mode 100644
index 0000000..37468e6
--- /dev/null
+++ b/bridge/monitor.c
@@ -0,0 +1,138 @@
+/*
+ * brmonitor.c		"br monitor"
+ *
+ *		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:	Stephen Hemminger <shemminger@vyatta.com>
+ *
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <time.h>
+#include <sys/socket.h>
+#include <sys/time.h>
+#include <net/if.h>
+#include <netinet/in.h>
+#include <linux/if_bridge.h>
+#include <linux/neighbour.h>
+#include <string.h>
+
+#include "utils.h"
+#include "br_common.h"
+
+
+static void usage(void) __attribute__((noreturn));
+int prefix_banner;
+
+static void usage(void)
+{
+	fprintf(stderr, "Usage: br monitor\n");
+	exit(-1);
+}
+
+static int show_mark(FILE *fp, const struct nlmsghdr *n)
+{
+	char *tstr;
+	time_t secs = ((__u32*)NLMSG_DATA(n))[0];
+	long usecs = ((__u32*)NLMSG_DATA(n))[1];
+	tstr = asctime(localtime(&secs));
+	tstr[strlen(tstr)-1] = 0;
+	fprintf(fp, "Timestamp: %s %lu us\n", tstr, usecs);
+	return 0;
+}
+
+int accept_msg(const struct sockaddr_nl *who,
+	       struct nlmsghdr *n, void *arg)
+{
+	FILE *fp = arg;
+
+	if (timestamp)
+		print_timestamp(fp);
+
+	switch (n->nlmsg_type) {
+	case RTM_NEWLINK:
+	case RTM_DELLINK:
+		if (prefix_banner)
+			fprintf(fp, "[LINK]");
+
+		return print_linkinfo(who, n, arg);
+
+	case RTM_NEWNEIGH:
+	case RTM_DELNEIGH:
+		if (prefix_banner)
+			fprintf(fp, "[NEIGH]");
+		return print_fdb(who, n, arg);
+
+	case 15:
+		return show_mark(fp, n);
+
+	default:
+		return 0;
+	}
+	
+
+}
+
+int do_monitor(int argc, char **argv)
+{
+	char *file = NULL;
+	unsigned groups = ~RTMGRP_TC;
+	int llink=0;
+	int lneigh=0;
+
+	rtnl_close(&rth);
+
+	while (argc > 0) {
+		if (matches(*argv, "file") == 0) {
+			NEXT_ARG();
+			file = *argv;
+		} else if (matches(*argv, "link") == 0) {
+			llink=1;
+			groups = 0;
+		} else if (matches(*argv, "fdb") == 0) {
+			lneigh = 1;
+			groups = 0;
+		} else if (strcmp(*argv, "all") == 0) {
+			groups = ~RTMGRP_TC;
+			prefix_banner=1;
+		} else if (matches(*argv, "help") == 0) {
+			usage();
+		} else {
+			fprintf(stderr, "Argument \"%s\" is unknown, try \"br monitor help\".\n", *argv);
+			exit(-1);
+		}
+		argc--;	argv++;
+	}
+
+	if (llink)
+		groups |= nl_mgrp(RTNLGRP_LINK);
+
+	if (lneigh) {
+		groups |= nl_mgrp(RTNLGRP_NEIGH);
+	}
+
+	if (file) {
+		FILE *fp;
+		fp = fopen(file, "r");
+		if (fp == NULL) {
+			perror("Cannot fopen");
+			exit(-1);
+		}
+		return rtnl_from_file(fp, accept_msg, stdout);
+	}
+
+	if (rtnl_open(&rth, groups) < 0)
+		exit(1);
+	ll_init_map(&rth);
+
+	if (rtnl_listen(&rth, accept_msg, stdout) < 0)
+		exit(2);
+
+	return 0;
+}
+