linux: use CLOCK_BOOTTIME if available

Use CLOCK_BOOTTIME to calculate the system uptime. Fall back to CLOCK_MONOTONIC if CLOCK_BOOTTIME is not available (all pre-2.6.39 kernels). The problem with CLOCK_MONOTONIC is that it doesn't increase when the system is suspended, making the uptime differ from what the uptime(1) tool reports.
joyent · Mar 19, 2012 · 49d4e18 · 49d4e18
1 parent 379ca42
commit 49d4e18
Showing 1 changed file with 26 additions and 12 deletions.
diff --git a/src/unix/linux/core.c b/src/unix/linux/core.c
@@ -48,6 +48,14 @@
 #undef NANOSEC
 #define NANOSEC 1000000000
 
+/* This is rather annoying: CLOCK_BOOTTIME lives in <linux/time.h> but we can't
+ * include that file because it conflicts with <time.h>. We'll just have to
+ * define it ourselves.
+ */
+#ifndef CLOCK_BOOTTIME
+# define CLOCK_BOOTTIME 7
+#endif
+
 static char buf[MAXPATHLEN + 1];
 
 static struct {
@@ -267,22 +275,28 @@ uv_err_t uv_resident_set_memory(size_t* rss) {
 
 
 uv_err_t uv_uptime(double* uptime) {
-#ifdef CLOCK_MONOTONIC
+  static volatile int no_clock_boottime;
   struct timespec now;
-  if (0 == clock_gettime(CLOCK_MONOTONIC, &now)) {
-    *uptime = now.tv_sec;
-    *uptime += (double)now.tv_nsec / 1000000000.0;
-    return uv_ok_;
+  int r;
+
+  /* Try CLOCK_BOOTTIME first, fall back to CLOCK_MONOTONIC if not available
+   * (pre-2.6.39 kernels). CLOCK_MONOTONIC doesn't increase when the system
+   * is suspended.
+   */
+  if (no_clock_boottime) {
+    retry: r = clock_gettime(CLOCK_MONOTONIC, &now);
   }
-  return uv__new_sys_error(errno);
-#else
-  struct sysinfo info;
-  if (sysinfo(&info) < 0) {
-    return uv__new_sys_error(errno);
+  else if ((r = clock_gettime(CLOCK_BOOTTIME, &now)) && errno == EINVAL) {
+    no_clock_boottime = 1;
+    goto retry;
   }
-  *uptime = (double)info.uptime;
+
+  if (r)
+    return uv__new_sys_error(errno);
+
+  *uptime = now.tv_sec;
+  *uptime += (double)now.tv_nsec / 1000000000.0;
   return uv_ok_;
-#endif
 }