ss: display interface name as zone index when needed

This change enable the ss command to display the interface name as zone index
for local addresses when needed.

For this enhanced display *_diag stuff is needed.

It is based on a first version by Bernd Eckenfels.

example:
Netid  State   Recv-Q Send-Q                 Local Address:Port    Peer Address:Port
udp    UNCONN  0      0      fe80::20c:29ff:fe1f:7406%eth1:9999              :::*
udp    UNCONN  0      0                                 :::domain            :::*
tcp    LISTEN  0      3                                 :::domain            :::*
tcp    LISTEN  0      5      fe80::20c:29ff:fe1f:7410%eth2:99                :::*
Signed-off-by: Francois-Xavier Le Bail <fx.lebail@yahoo.com>

misc/ss.c

@@ -640,7 +640,7 @@ static const char *resolve_service(int port)
 	return buf;
 }
 
-static void formatted_print(const inet_prefix *a, int port)
+static void formatted_print(const inet_prefix *a, int port, unsigned int ifindex)
 {
 	char buf[1024];
 	const char *ap = buf;
@@ -663,7 +663,14 @@ static void formatted_print(const inet_prefix *a, int port)
 		else
 			est_len = addr_width + ((est_len-addr_width+3)/4)*4;
 	}
-	printf("%*s:%-*s ", est_len, ap, serv_width, resolve_service(port));
+	if (ifindex) {
+		const char *ifname = ll_index_to_name(ifindex);
+		const int len = strlen(ifname) + 1;  /* +1 for percent char */
+
+		printf("%*s%%%s:%-*s ", est_len - len, ap, ifname, serv_width,
+		       resolve_service(port));
+	} else
+		printf("%*s:%-*s ", est_len, ap, serv_width, resolve_service(port));
 }
 
 struct aafilter
@@ -1254,8 +1261,8 @@ static int tcp_show_line(char *line, const struct filter *f, int family)
 
 	printf("%-6d %-6d ", s.rq, s.wq);
 
-	formatted_print(&s.local, s.lport);
-	formatted_print(&s.remote, s.rport);
+	formatted_print(&s.local, s.lport, 0);
+	formatted_print(&s.remote, s.rport, 0);
 
 	if (show_options) {
 		if (s.timer) {
@@ -1507,8 +1514,8 @@ static int inet_show_sock(struct nlmsghdr *nlh, struct filter *f, int protocol)
 
 	printf("%-6d %-6d ", r->idiag_rqueue, r->idiag_wqueue);
 
-	formatted_print(&s.local, s.lport);
-	formatted_print(&s.remote, s.rport);
+	formatted_print(&s.local, s.lport, r->id.idiag_if);
+	formatted_print(&s.remote, s.rport, 0);
 
 	if (show_options) {
 		if (r->idiag_timer) {
@@ -2006,8 +2013,8 @@ static int dgram_show_line(char *line, const struct filter *f, int family)
 
 	printf("%-6d %-6d ", s.rq, s.wq);
 
-	formatted_print(&s.local, s.lport);
-	formatted_print(&s.remote, s.rport);
+	formatted_print(&s.local, s.lport, 0);
+	formatted_print(&s.remote, s.rport, 0);
 
 	if (show_users) {
 		char ubuf[4096];