[btimed] Use /proc/uptime when available

It turns out the boot time being returned to btimec is has not been
correct for quite a while.  There was probably a change to HZ which
isn't reflected properly in _SC_CLK_TCK.  This needs some more error
checking, but it works for now.

1 files changed, 15 insertions, 2 deletions

diff --git a/btimed.c b/btimed.c
index 68a045a..83a5af6 100644
--- a/btimed.c
+++ b/btimed.c
@@ -112,9 +112,22 @@ get_btime(void)
 {
 	unsigned int btime = 0;
 	long hertz = sysconf(_SC_CLK_TCK);
-	struct tms tms;
 
-	btime = time(0) - (times(&tms) / hertz);
+	btime = time(0);
+
+	if (access("/proc/uptime", F_OK | R_OK) == 0) {
+		FILE *proc_uptime;
+		unsigned long upsec = 0;
+	       	proc_uptime = fopen("/proc/uptime", "r");
+		fscanf(proc_uptime, "%lu.%*u %*u.%*u\n", &upsec);
+		fclose(proc_uptime);
+
+		btime -= upsec;
+	} else {
+		struct tms tms;
+
+		btime -= (times(&tms) / hertz);
+	}
 	btime = btime - (btime % 5) + 5;
 	return btime;
 }