ip: Support IFLA_TXQLEN in ip link command

Eric Dumazet a écrit :
> We currently use an expensive ioctl() to get device txqueuelen, while
> rtnetlink gave it to us for free. This patch speeds up ip link operation
> when many devices are registered.
>

Here is a 2nd version od this patch, not displaying "qlen 0" useless info

[PATCH iproute2] ip: Support IFLA_TXQLEN in ip link show command

We currently use an expensive ioctl() to get device txqueuelen, while
rtnetlink gave it to us for free. This patch speeds up ip link operation
when many devices are registered.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>

ip/ipaddress.c

@@ -130,26 +130,31 @@ static void print_operstate(FILE *f, __u8 state)
 		fprintf(f, "state %s ", oper_states[state]);
 }
 
-static void print_queuelen(FILE *f, const char *name)
+static void print_queuelen(FILE *f, struct rtattr *tb[IFLA_MAX + 1])
 {
-	struct ifreq ifr;
-	int s;
-
-	s = socket(AF_INET, SOCK_STREAM, 0);
-	if (s < 0)
-		return;
-
-	memset(&ifr, 0, sizeof(ifr));
-	strcpy(ifr.ifr_name, name);
-	if (ioctl(s, SIOCGIFTXQLEN, &ifr) < 0) {
-		fprintf(f, "ioctl(SIOCGIFXQLEN) failed: %s\n", strerror(errno));
+	int qlen;
+
+	if (tb[IFLA_TXQLEN])
+		qlen = *(int *)RTA_DATA(tb[IFLA_TXQLEN]);
+	else {
+		struct ifreq ifr;
+		int s = socket(AF_INET, SOCK_STREAM, 0);
+
+		if (s < 0)
+			return;
+
+		memset(&ifr, 0, sizeof(ifr));
+		strcpy(ifr.ifr_name, (char *)RTA_DATA(tb[IFLA_IFNAME]));
+		if (ioctl(s, SIOCGIFTXQLEN, &ifr) < 0) {
+			fprintf(f, "ioctl(SIOCGIFXQLEN) failed: %s\n", strerror(errno));
+			close(s);
+			return;
+		}
 		close(s);
-		return;
+		qlen = ifr.ifr_qlen;
 	}
-	close(s);
-
-	if (ifr.ifr_qlen)
-		fprintf(f, "qlen %d", ifr.ifr_qlen);
+	if (qlen)
+		fprintf(f, "qlen %d", qlen);
 }
 
 static void print_linktype(FILE *fp, struct rtattr *tb)
@@ -286,7 +291,7 @@ int print_linkinfo(const struct sockaddr_nl *who,
 		print_operstate(fp, *(__u8 *)RTA_DATA(tb[IFLA_OPERSTATE]));
 		
 	if (filter.showqueue)
-		print_queuelen(fp, (char*)RTA_DATA(tb[IFLA_IFNAME]));
+		print_queuelen(fp, tb);
 
 	if (!filter.family || filter.family == AF_PACKET) {
 		SPRINT_BUF(b1);