mtu: write discovered mtu to interface mtu

3 files changed, 110 insertions, 20 deletions

diff --git a/mtu.c b/mtu.c
index e2fb7c3..1ef1bce 100644
--- a/mtu.c
+++ b/mtu.c
@@ -5,6 +5,8 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <linux/if.h>
+#include <linux/sockios.h>
 #include <netinet/ip_icmp.h>
 
 #include "icmp.h"
@@ -17,7 +19,8 @@ static void usage(void)
 	fprintf(stderr,
 		"usage: mtu -i <mtu-size> <host>\n"
 		"       mtu -I <host>\n"
-		"       mtu -d <host>\n");
+		"       mtu -d <host>\n"
+		"       mtu -D <host>\n");
 	exit(3);
 }
 
@@ -58,16 +61,14 @@ static int do_ping(int seq, int size)
 	return -1;
 }
 
-static void do_discover(void)
+static int discover_mtu(void)
 {
 	int seq = 1;
 	int low_mtu, high_mtu, try_mtu;
 
 	/* Check if the host is up */
-	if (do_ping(seq++, 0) < 0) {
-		fprintf(stderr, "Host is not up\n");
-		return;
-	}
+	if (do_ping(seq++, 0) < 0)
+		return -1;
 
 	/* Check if there is no PMTU or if PMTU discovery works */
 	low_mtu = do_ping(seq++, 1500);
@@ -85,7 +86,59 @@ static void do_discover(void)
 		low_mtu = 1500;
 	}
 
-	fprintf(stdout, "%d\n", low_mtu);
+	return low_mtu;
+}
+
+static void do_discover(void)
+{
+	int mtu;
+
+	mtu = discover_mtu();
+	if (mtu > 0)
+		fprintf(stdout, "%d\n", mtu);
+	else
+		fprintf(stderr, "Host is not up\n");
+}
+
+static int set_mtu(const char *dev, int mtu)
+{
+	struct ifreq ifr;
+	int fd;
+
+	fd = socket(PF_INET, SOCK_DGRAM, 0);
+	if (fd < 0)
+		return -1;
+
+	memset(&ifr, 0, sizeof(ifr));
+	strncpy(ifr.ifr_name, dev, IFNAMSIZ);
+	ifr.ifr_mtu = mtu;
+	if (ioctl(fd, SIOCSIFMTU, &ifr) < 0) {
+		perror("SIOCSIFMTU");
+		close(fd);
+		return -1;
+	}
+	close(fd);
+	return 0; 
+}
+
+static void do_discover_and_write(void)
+{
+	int mtu;
+	char iface[IFNAMSIZ];
+
+	mtu = discover_mtu();
+	if (mtu < 0) {
+		fprintf(stderr, "Failed to determine MTU\n");
+		return;
+	}
+
+	if (!netlink_route_get(&to, NULL, iface)) {
+		fprintf(stderr, "Failed to determine route interface\n");
+		return;
+	}
+
+	printf("Writing %d to %s\n", mtu, iface);
+	set_mtu(iface, mtu);
 }
 
 static void do_inject(void)
@@ -121,7 +174,7 @@ static void do_inject_pmtu(void)
 {
 	u_int16_t mtu;
 
-	if (netlink_route_get(&to, &mtu) < 0) {
+	if (!netlink_route_get(&to, &mtu, NULL)) {
 		fprintf(stderr, "Failed to determine Path MTU\n");
 		return;
 	}
@@ -139,8 +192,11 @@ int main(int argc, char **argv)
 	char *target;
 	int opt;
 
-	while ((opt = getopt(argc, argv, "dIi:")) != -1) {
+	while ((opt = getopt(argc, argv, "DdIi:")) != -1) {
 		switch (opt) {
+		case 'D':
+			action = do_discover_and_write;
+			break;
 		case 'd':
 			action = do_discover;
 			break;
diff --git a/netlink.c b/netlink.c
index 3e85e6f..5e43116 100644
--- a/netlink.c
+++ b/netlink.c
@@ -220,16 +220,21 @@ out:
 	return ret;
 }
 
-int netlink_route_get(struct sockaddr *dst, u_int16_t *mtu)
+int netlink_route_get(struct sockaddr *dst, u_int16_t *mtu, char *ifname)
 {
 	struct {
 		struct nlmsghdr 	n;
-		struct rtmsg 		r;
+		union {
+			struct rtmsg		r;
+			struct ifinfomsg	i;
+		};
 		char   			buf[1024];
 	} req;
 	struct rtmsg *r = NLMSG_DATA(&req.n);
 	struct rtattr *rta[RTA_MAX+1];
 	struct rtattr *rtax[RTAX_MAX+1];
+	struct rtattr *ifla[IFLA_MAX+1];
+	int index;
 
 	memset(&req, 0, sizeof(req));
 	req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct rtmsg));
@@ -243,15 +248,44 @@ int netlink_route_get(struct sockaddr *dst, u_int16_t *mtu)
 	if (!netlink_talk(&req.n, sizeof(req), &req.n))
 		return FALSE;
 
-	netlink_parse_rtattr(rta, RTA_MAX, RTM_RTA(r), RTM_PAYLOAD(&req.n));
-	if (rta[RTA_METRICS] == NULL)
-		return FALSE;
+	netlink_parse_rtattr(rta, RTA_MAX, RTM_RTA(r),
+			     RTM_PAYLOAD(&req.n));
 
-	netlink_parse_rtattr(rtax, RTAX_MAX, RTA_DATA(rta[RTA_METRICS]),
-			     RTA_PAYLOAD(rta[RTA_METRICS]));
-	if (rtax[RTAX_MTU] == NULL)
-		return FALSE;
+	if (mtu != NULL) {
+		if (rta[RTA_METRICS] == NULL)
+			return FALSE;
+
+		netlink_parse_rtattr(rtax, RTAX_MAX,
+				     RTA_DATA(rta[RTA_METRICS]),
+				     RTA_PAYLOAD(rta[RTA_METRICS]));
+		if (rtax[RTAX_MTU] == NULL)
+			return FALSE;
+
+		*mtu = *(int*) RTA_DATA(rtax[RTAX_MTU]);
+	}
+
+	if (ifname != NULL) {
+		if (rta[RTA_OIF] == NULL)
+			return FALSE;
+
+		index = *(int*) RTA_DATA(rta[RTA_OIF]);
+
+		memset(&req, 0, sizeof(req));
+		req.n.nlmsg_len = NLMSG_LENGTH(sizeof(struct ifinfomsg));
+		req.n.nlmsg_flags = NLM_F_REQUEST;
+		req.n.nlmsg_type = RTM_GETLINK;
+		req.i.ifi_index = index;
+		if (!netlink_talk(&req.n, sizeof(req), &req.n))
+			return FALSE;
+
+		netlink_parse_rtattr(ifla, IFLA_MAX, IFLA_RTA(r),
+				     IFLA_PAYLOAD(&req.n));
+		if (ifla[IFLA_IFNAME] == NULL)
+			return FALSE;
+
+		memcpy(ifname, RTA_DATA(ifla[IFLA_IFNAME]),
+		       RTA_PAYLOAD(ifla[IFLA_IFNAME]));
+	}
 
-	*mtu = *(int*) RTA_DATA(rtax[RTAX_MTU]);
 	return TRUE;
 }
diff --git a/netlink.h b/netlink.h
index 8c44925..4e2ceb2 100644
--- a/netlink.h
+++ b/netlink.h
@@ -1,6 +1,6 @@
 #ifndef PINGU_NETLINK_H
 #define PINGU_NETLINK_H
 
-int netlink_route_get(struct sockaddr *dst, u_int16_t *mtu);
+int netlink_route_get(struct sockaddr *dst, u_int16_t *mtu, char *ifname);
 
 #endif