Fix various timer-related issues

Changes:

    * Replace usage of gettimeofday() with clock_gettime() in the main
      event loop, patty_ax25_server_run(), as gettimeofday() apparently
      goes backwards in time occasionally, as per:

        https://bugzilla.redhat.com/show_bug.cgi?id=174390

      Thanks Iain MM0ROR!

    * Fix patty_timer_expired() to properly return true if the
      remaining number of seconds is zero, but the remaining higher
      precision time is less than zero

    * Implement patty_timer_sub() to subtract two struct timespec
      values, as glibc lacks timespecsub()

include/patty/timer.h

@@ -9,7 +9,7 @@ enum patty_timer_flags {
 };
 
 typedef struct _patty_timer {
-    struct timeval t;
+    struct timespec t;
     uint32_t flags;
 } patty_timer;
 
@@ -24,7 +24,11 @@ void patty_timer_start(patty_timer *timer,
 
 void patty_timer_stop(patty_timer *timer);
 
+void patty_timer_sub(struct timespec *a,
+                     struct timespec *b,
+                     struct timespec *c);
+
 void patty_timer_tick(patty_timer *timer,
-                      struct timeval *elapsed);
+                      struct timespec *elapsed);
 
 #endif /* _PATTY_TIMER_H */

src/server.c

@@ -3,6 +3,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <fcntl.h>
+#include <time.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/socket.h>
@@ -20,7 +21,7 @@ struct _patty_ax25_server {
     int fd,     /* fd of UNIX domain socket */
         fd_max;
 
-    struct timeval elapsed;
+    struct timespec elapsed;
 
     fd_set fds_watch, /* fds to monitor with select() */
            fds_r;     /* fds select()ed for reading */
@@ -2018,14 +2019,15 @@ int patty_ax25_server_run(patty_ax25_server *server) {
     while (1) {
         int nready;
 
-        struct timeval timeout = { 1, 0 },
+        struct timeval timeout = { 1, 0 };
-                       before,
+
-                       after;
+        struct timespec before,
+                        after;
 
         memcpy(&server->fds_r, &server->fds_watch, sizeof(server->fds_r));
 
-        if (gettimeofday(&before, NULL) < 0) {
+        if (clock_gettime(CLOCK_MONOTONIC, &before) < 0) {
-            goto error_gettimeofday;
+            goto error_clock_gettime;
         }
 
         if ((nready = select( server->fd_max,
@@ -2036,11 +2038,11 @@ int patty_ax25_server_run(patty_ax25_server *server) {
             goto error_io;
         }
 
-        if (gettimeofday(&after, NULL) < 0) {
+        if (clock_gettime(CLOCK_MONOTONIC, &after) < 0) {
-            goto error_gettimeofday;
+            goto error_clock_gettime;
         }
 
-        timersub(&after, &before, &server->elapsed);
+        patty_timer_sub(&after, &before, &server->elapsed);
 
         if (handle_socks(server) < 0) {
             goto error_io;
@@ -2065,7 +2067,7 @@ int patty_ax25_server_run(patty_ax25_server *server) {
 
     return 0;
 
-error_gettimeofday:
+error_clock_gettime:
 error_io:
     close(server->fd);
 

src/timer.c

@@ -5,12 +5,17 @@ int patty_timer_running(patty_timer *timer) {
 }
 
 int patty_timer_expired(patty_timer *timer) {
-    return (timer->flags & PATTY_TIMER_RUNNING) && timer->t.tv_sec <= 0? 1: 0;
+    if (!(timer->flags & PATTY_TIMER_RUNNING)) {
+        return 0;
+    }
+
+    return timer->t.tv_sec < 0
+       || (timer->t.tv_sec == 0 && timer->t.tv_nsec <= 0)? 1: 0;
 }
 
 void patty_timer_clear(patty_timer *timer) {
     timer->t.tv_sec  = 0;
-    timer->t.tv_usec = 0;
+    timer->t.tv_nsec = 0;
 
     timer->flags &= ~PATTY_TIMER_RUNNING;
 }
@@ -18,7 +23,7 @@ void patty_timer_clear(patty_timer *timer) {
 void patty_timer_start(patty_timer *timer,
                        time_t ms) {
     timer->t.tv_sec  =  ms / 1000;
-    timer->t.tv_usec = (ms % 1000) * 1000;
+    timer->t.tv_nsec = (ms % 1000) * 1000000;
 
     timer->flags |= PATTY_TIMER_RUNNING;
 }
@@ -27,16 +32,24 @@ void patty_timer_stop(patty_timer *timer) {
     timer->flags &= ~PATTY_TIMER_RUNNING;
 }
 
+void patty_timer_sub(struct timespec *a,
+                     struct timespec *b,
+                     struct timespec *c) {
+    c->tv_nsec  = a->tv_nsec - b->tv_nsec;
+    c->tv_sec   = a->tv_sec  - b->tv_sec - (c->tv_nsec / 1000000000);
+    c->tv_nsec %= 1000000000;
+}
+
 void patty_timer_tick(patty_timer *timer,
-                      struct timeval *elapsed) {
+                      struct timespec *elapsed) {
-    struct timeval res;
+    struct timespec res;
 
     if (!(timer->flags & PATTY_TIMER_RUNNING)) {
         return;
     }
 
-    timersub(&timer->t, elapsed, &res);
+    patty_timer_sub(&timer->t, elapsed, &res);
 
     timer->t.tv_sec  = res.tv_sec;
-    timer->t.tv_usec = res.tv_usec;
+    timer->t.tv_nsec = res.tv_nsec;
 }