traceroute: properly reduce poll timeout

This removes the problem where during the time we wait to declare
a target as unresponsive we receive an unrelated ICMP packet.
If there is enough traffic, this can make traceroute hang as
it never declares the target as unresponsive.

function                                             old     new   delta
common_traceroute_main                              4196    4261     +65

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/networking/traceroute.c b/networking/traceroute.c
index 96f9d3472da1f0943c9f85f71d4d2374993b175b..85181ab8d77a8d4b54f7e11080daff4e1e5f0321 100644 (file)
--- a/networking/traceroute.c
+++ b/networking/traceroute.c
@@ -398,18 +398,23 @@ static len_and_sockaddr* dup_sockaddr(const len_and_sockaddr *lsa)
 
 
 static int
-wait_for_reply(len_and_sockaddr *from_lsa, struct sockaddr *to)
+wait_for_reply(len_and_sockaddr *from_lsa, struct sockaddr *to, unsigned *timestamp_us, int *left_ms)
 {
        struct pollfd pfd[1];
        int read_len = 0;
 
        pfd[0].fd = rcvsock;
        pfd[0].events = POLLIN;
-       if (safe_poll(pfd, 1, waittime * 1000) > 0) {
+       if (*left_ms >= 0 && safe_poll(pfd, 1, *left_ms) > 0) {
+               unsigned t;
+
                read_len = recv_from_to(rcvsock,
                                recv_pkt, sizeof(recv_pkt),
-                               /*flags:*/ 0,
+                               /*flags:*/ MSG_DONTWAIT,
                                &from_lsa->u.sa, to, from_lsa->len);
+               t = monotonic_us();
+               *left_ms -= (t - *timestamp_us) / 1000;
+               *timestamp_us = t;
        }
 
        return read_len;
@@ -730,7 +735,7 @@ packet_ok(int read_len, len_and_sockaddr *from_lsa,
                        type, pr_type(type), icp->icmp6_code);
 
                read_len -= sizeof(struct icmp6_hdr);
-               for (i = 0; i < read_len ; i++) {
+               for (i = 0; i < read_len; i++) {
                        if (i % 16 == 0)
                                printf("%04x:", i);
                        if (i % 4 == 0)
@@ -819,7 +824,6 @@ print_delta_ms(unsigned t1p, unsigned t2p)
 static int
 common_traceroute_main(int op, char **argv)
 {
-       int i;
        int minpacket;
        int tos = 0;
        int max_ttl = 30;
@@ -973,6 +977,7 @@ common_traceroute_main(int op, char **argv)
 #if ENABLE_FEATURE_TRACEROUTE_SOURCE_ROUTE && defined IP_OPTIONS
                if (lsrr > 0) {
                        unsigned char optlist[MAX_IPOPTLEN];
+                       unsigned size;
 
                        /* final hop */
                        gwlist[lsrr] = dest_lsa->u.sin.sin_addr.s_addr;
@@ -982,14 +987,14 @@ common_traceroute_main(int op, char **argv)
                        optlist[0] = IPOPT_NOP;
                        /* loose source route option */
                        optlist[1] = IPOPT_LSRR;
-                       i = lsrr * sizeof(gwlist[0]);
-                       optlist[2] = i + 3;
+                       size = lsrr * sizeof(gwlist[0]);
+                       optlist[2] = size + 3;
                        /* pointer to LSRR addresses */
                        optlist[3] = IPOPT_MINOFF;
-                       memcpy(optlist + 4, gwlist, i);
+                       memcpy(optlist + 4, gwlist, size);
 
                        if (setsockopt(sndsock, IPPROTO_IP, IP_OPTIONS,
-                                       (char *)optlist, i + sizeof(gwlist[0])) < 0) {
+                                       (char *)optlist, size + sizeof(gwlist[0])) < 0) {
                                bb_perror_msg_and_die("IP_OPTIONS");
                        }
                }
@@ -1103,28 +1108,34 @@ common_traceroute_main(int op, char **argv)
                int unreachable = 0; /* counter */
                int gotlastaddr = 0; /* flags */
                int got_there = 0;
-               int first = 1;
 
                printf("%2d", ttl);
                for (probe = 0; probe < nprobes; ++probe) {
                        int read_len;
                        unsigned t1;
                        unsigned t2;
+                       int left_ms;
                        struct ip *ip;
 
-                       if (!first && pausemsecs > 0)
-                               usleep(pausemsecs * 1000);
                        fflush_all();
+                       if (probe != 0 && pausemsecs > 0)
+                               usleep(pausemsecs * 1000);
 
-                       t1 = monotonic_us();
                        send_probe(++seq, ttl);
+                       t2 = t1 = monotonic_us();
+
+                       left_ms = waittime * 1000;
+                       while ((read_len = wait_for_reply(from_lsa, to, &t2, &left_ms)) != 0) {
+                               int icmp_code;
+
+                               /* Recv'ed a packet, or read error */
+                               /* t2 = monotonic_us() - set by wait_for_reply */
 
-                       first = 0;
-                       while ((read_len = wait_for_reply(from_lsa, to)) != 0) {
-                               t2 = monotonic_us();
-                               i = packet_ok(read_len, from_lsa, to, seq);
+                               if (read_len < 0)
+                                       continue;
+                               icmp_code = packet_ok(read_len, from_lsa, to, seq);
                                /* Skip short packet */
-                               if (i == 0)
+                               if (icmp_code == 0)
                                        continue;
 
                                if (!gotlastaddr
@@ -1143,10 +1154,10 @@ common_traceroute_main(int op, char **argv)
                                                printf(" (%d)", ip->ip_ttl);
 
                                /* time exceeded in transit */
-                               if (i == -1)
+                               if (icmp_code == -1)
                                        break;
-                               i--;
-                               switch (i) {
+                               icmp_code--;
+                               switch (icmp_code) {
 #if ENABLE_TRACEROUTE6
                                case ICMP6_DST_UNREACH_NOPORT << 8:
                                        got_there = 1;
@@ -1219,16 +1230,18 @@ common_traceroute_main(int op, char **argv)
                                        ++unreachable;
                                        break;
                                default:
-                                       printf(" !<%d>", i);
+                                       printf(" !<%d>", icmp_code);
                                        ++unreachable;
                                        break;
                                }
                                break;
-                       }
+                       } /* while (wait and read a packet) */
+
                        /* there was no packet at all? */
                        if (read_len == 0)
                                printf("  *");
-               }
+               } /* for (nprobes) */
+
                bb_putchar('\n');
                if (got_there
                 || (unreachable > 0 && unreachable >= nprobes - 1)