Use POSIX timers if available.

This protects against clock stepping if CLOCK_MONOTONIC is implemented.

Makefile

@@ -6,6 +6,8 @@ DEFINES = $(PLATFORM_DEFINES)
 
 CFLAGS = $(CDEBUGFLAGS) $(DEFINES) $(EXTRA_DEFINES)
 
+LDLIBS = -lrt
+
 SRCS = babel.c net.c kernel.c util.c network.c source.c neighbour.c \
        route.c xroute.c message.c resend.c filter.c
 

util.c

@@ -68,6 +68,32 @@ seqno_plus(unsigned short s, int plus)
 int
 gettime(struct timeval *tv)
 {
+#if defined(_POSIX_TIMERS) && _POSIX_TIMERS > 0 && defined(CLOCK_MONOTONIC)
+    static int have_posix_clocks = -1;
+
+    if(have_posix_clocks < 0) {
+        struct timespec ts;
+        int rc;
+        rc = clock_gettime(CLOCK_MONOTONIC, &ts);
+        if(rc < 0) {
+            have_posix_clocks = 0;
+        } else {
+            have_posix_clocks = 1;
+        }
+    }
+
+    if(have_posix_clocks) {
+        struct timespec ts;
+        int rc;
+        rc = clock_gettime(CLOCK_MONOTONIC, &ts);
+        if(rc < 0)
+            return rc;
+        tv->tv_sec = ts.tv_sec;
+        tv->tv_usec = ts.tv_nsec / 1000;
+        return rc;
+    }
+#endif
+
     return gettimeofday(tv, NULL);
 }