route: show originator PID in netlink monitor

Replacing rtsock with netlink also means providing similar tracing facilities,
rtsock provides `route -n monitor` interface, where each message can be traced
to the originating PID.
This diff closes the feature gap between rtsock and netlink in that regard.

Netlink works slightly differently from rtsock, as it is a generic message
"broker". It calls some kernel KPIs and returns the result to the caller.
Other Netlink consumers gets notified on the changed kernel state using the
relevant subsystem callbacks. Typically, it is close to impossible to pass
some data through these KPIs to enhance the notification.

This diff approaches the problem by using osd(9) to assign the relevant
socket pointer (`'nlp`) to the per-socket taskqueue execution thread.
This change allows to recover the pointer in the aforementioned notification
callbacks and extract some additional data.
Using `osd(9)` (and adding additional metadata) to the notification receiver
comes with some additional cost attached, so this interface needs to be
enabled explicitly by using a newly-created `NETLINK_MSG_INFO` `SOL_NETLINK`
socket option.

The actual medatadata (which includes the originator PID) is provided via
control messages. To enable extensibility, the control message data is
encoded in the standard netlink(TLV-based) fashion. The list of the
currently-provided properties can be found in `nlmsginfo_attrs`.
snl(3) is extended to enable decoding of netlink messages with metadata
(`snl_read_message_dbg()` stores the parsed structure in the provided buffer).

Differential Revision: https://reviews.freebsd.org/D39391

sbin/route/route_netlink.c

@@ -39,8 +39,11 @@ int flushroutes_fib_nl(int fib, int af);
 void monitor_nl(int fib);
 
 struct nl_helper;
-static void print_getmsg(struct nl_helper *h, struct nlmsghdr *hdr, struct sockaddr *dst);
-static void print_nlmsg(struct nl_helper *h, struct nlmsghdr *hdr);
+struct snl_msg_info;
+static void print_getmsg(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct sockaddr *dst);
+static void print_nlmsg(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct snl_msg_info *cinfo);
 
 #define s6_addr32 __u6_addr.__u6_addr32
 #define	bitcount32(x)	__bitcount32((uint32_t)(x))
@@ -434,9 +437,9 @@ print_prefix(struct nl_helper *h, char *buf, int bufsize, struct sockaddr *sa, i
 		snprintf(buf + sz, bufsize - sz, "/%d", plen);
 }
 
-
 static int
-print_line_prefix(const char *cmd, const char *name)
+print_line_prefix(struct nlmsghdr *hdr, struct snl_msg_info *cinfo,
+    const char *cmd, const char *name)
 {
 	struct timespec tp;
 	struct tm tm;
@@ -446,7 +449,8 @@ print_line_prefix(const char *cmd, const char *name)
 	localtime_r(&tp.tv_sec, &tm);
 
 	strftime(buf, sizeof(buf), "%T", &tm);
-	int len = printf("%s.%03ld %s %s ", buf, tp.tv_nsec / 1000000, cmd, name);
+	int len = printf("%s.%03ld PID %4u %s %s ", buf, tp.tv_nsec / 1000000,
+	    cinfo->process_id, cmd, name);
 
 	return (len);
 }
@@ -498,7 +502,8 @@ print_nlmsg_route_nhop(struct nl_helper *h, struct snl_parsed_route *r,
 }
 
 static void
-print_nlmsg_route(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg_route(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct snl_msg_info *cinfo)
 {
 	struct snl_parsed_route r = { .rtax_weight = RT_DEFAULT_WEIGHT };
 	struct snl_state *ss = &h->ss_cmd;
@@ -509,7 +514,7 @@ print_nlmsg_route(struct nl_helper *h, struct nlmsghdr *hdr)
 	// 20:19:41.333 add route 10.0.0.0/24 gw 10.0.0.1 ifp vtnet0 mtu 1500 table inet.0
 
 	const char *cmd = get_action_name(hdr, RTM_NEWROUTE);
-	int len = print_line_prefix(cmd, "route");
+	int len = print_line_prefix(hdr, cinfo, cmd, "route");
 
 	char buf[128];
 	print_prefix(h, buf, sizeof(buf), r.rta_dst, r.rtm_dst_len);
@@ -564,7 +569,8 @@ static const char *operstate[] = {
 };
 
 static void
-print_nlmsg_link(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg_link(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct snl_msg_info *cinfo)
 {
 	struct snl_parsed_link l = {};
 	struct snl_state *ss = &h->ss_cmd;
@@ -574,7 +580,7 @@ print_nlmsg_link(struct nl_helper *h, struct nlmsghdr *hdr)
 
 	// 20:19:41.333 add iface#3 vtnet0 admin UP oper UP mtu 1500 table inet.0
 	const char *cmd = get_action_name(hdr, RTM_NEWLINK);
-	print_line_prefix(cmd, "iface");
+	print_line_prefix(hdr, cinfo, cmd, "iface");
 
 	printf("iface#%u %s ", l.ifi_index, l.ifla_ifname);
 	printf("admin %s ", (l.ifi_flags & IFF_UP) ? "UP" : "DOWN");
@@ -587,7 +593,8 @@ print_nlmsg_link(struct nl_helper *h, struct nlmsghdr *hdr)
 }
 
 static void
-print_nlmsg_addr(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg_addr(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct snl_msg_info *cinfo)
 {
 	struct snl_parsed_addr attrs = {};
 	struct snl_state *ss = &h->ss_cmd;
@@ -597,7 +604,7 @@ print_nlmsg_addr(struct nl_helper *h, struct nlmsghdr *hdr)
 
 	// add addr 192.168.1.1/24 iface vtnet0
 	const char *cmd = get_action_name(hdr, RTM_NEWADDR);
-	print_line_prefix(cmd, "addr");
+	print_line_prefix(hdr, cinfo, cmd, "addr");
 
 	char buf[128];
 	struct sockaddr *addr = attrs.ifa_local ? attrs.ifa_local : attrs.ifa_address;
@@ -636,7 +643,8 @@ static const char *nudstate[] = {
 
 
 static void
-print_nlmsg_neigh(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg_neigh(struct nl_helper *h, struct nlmsghdr *hdr,
+    struct snl_msg_info *cinfo)
 {
 	struct snl_parsed_neigh attrs = {};
 	struct snl_state *ss = &h->ss_cmd;
@@ -646,7 +654,7 @@ print_nlmsg_neigh(struct nl_helper *h, struct nlmsghdr *hdr)
 
 	// add addr 192.168.1.1 state %s lladdr %s iface vtnet0
 	const char *cmd = get_action_name(hdr, RTM_NEWNEIGH);
-	print_line_prefix(cmd, "neigh");
+	print_line_prefix(hdr, cinfo, cmd, "neigh");
 
 	char buf[128];
 	print_prefix(h, buf, sizeof(buf), attrs.nda_dst, -1);
@@ -694,32 +702,35 @@ print_nlmsg_neigh(struct nl_helper *h, struct nlmsghdr *hdr)
 }
 
 static void
-print_nlmsg_generic(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg_generic(struct nl_helper *h, struct nlmsghdr *hdr, struct snl_msg_info *cinfo)
 {
+	const char *cmd = get_action_name(hdr, 0);
+	print_line_prefix(hdr, cinfo, cmd, "unknown message");
+	printf(" type %u\n", hdr->nlmsg_type);
 }
 
 static void
-print_nlmsg(struct nl_helper *h, struct nlmsghdr *hdr)
+print_nlmsg(struct nl_helper *h, struct nlmsghdr *hdr, struct snl_msg_info *cinfo)
 {
 	switch (hdr->nlmsg_type) {
 	case RTM_NEWLINK:
 	case RTM_DELLINK:
-		print_nlmsg_link(h, hdr);
+		print_nlmsg_link(h, hdr, cinfo);
 		break;
 	case RTM_NEWADDR:
 	case RTM_DELADDR:
-		print_nlmsg_addr(h, hdr);
+		print_nlmsg_addr(h, hdr, cinfo);
 		break;
 	case RTM_NEWROUTE:
 	case RTM_DELROUTE:
-		print_nlmsg_route(h, hdr);
+		print_nlmsg_route(h, hdr, cinfo);
 		break;
 	case RTM_NEWNEIGH:
 	case RTM_DELNEIGH:
-		print_nlmsg_neigh(h, hdr);
+		print_nlmsg_neigh(h, hdr, cinfo);
 		break;
 	default:
-		print_nlmsg_generic(h, hdr);
+		print_nlmsg_generic(h, hdr, cinfo);
 	}
 
 	snl_clear_lb(&h->ss_cmd);
@@ -748,6 +759,10 @@ monitor_nl(int fib)
 #endif
 	};
 
+	int optval = 1;
+	socklen_t optlen = sizeof(optval);
+	setsockopt(ss_event.fd, SOL_NETLINK, NETLINK_MSG_INFO, &optval, optlen);
+
 	for (unsigned int i = 0; i < NL_ARRAY_LEN(groups); i++) {
 		int error;
 		int optval = groups[i];
@@ -758,11 +773,11 @@ monitor_nl(int fib)
 			warn("Unable to subscribe to group %d", optval);
 	}
 
+	struct snl_msg_info attrs = {};
 	struct nlmsghdr *hdr;
-	while ((hdr = snl_read_message(&ss_event)) != NULL)
+	while ((hdr = snl_read_message_dbg(&ss_event, &attrs)) != NULL)
 	{
-		// printf("-- MSG type %d--\n", hdr->nlmsg_type);
-		print_nlmsg(&h, hdr);
+		print_nlmsg(&h, hdr, &attrs);
 		snl_clear_lb(&h.ss_cmd);
 		snl_clear_lb(&ss_event);
 	}
@@ -814,8 +829,10 @@ flushroute_one(struct nl_helper *h, struct snl_parsed_route *r)
 		return (true);
 	};
 
-	if (verbose)
-		print_nlmsg(h, hdr);
+	if (verbose) {
+		struct snl_msg_info attrs = {};
+		print_nlmsg(h, hdr, &attrs);
+	}
 	else {
 		if (r->rta_multipath != NULL) {
 			for (int i = 0; i < r->rta_multipath->num_nhops; i++) {
@@ -863,8 +880,10 @@ flushroutes_fib_nl(int fib, int af)
 
 		if (!snl_parse_nlmsg(&ss, hdr, &snl_rtm_route_parser, &r))
 			continue;
-		if (verbose)
-			print_nlmsg(&h, hdr);
+		if (verbose) {
+			struct snl_msg_info attrs = {};
+			print_nlmsg(&h, hdr, &attrs);
+		}
 		if (r.rta_table != (uint32_t)fib || r.rtm_family != af)
 			continue;
 		if ((r.rta_rtflags & RTF_GATEWAY) == 0)