Libc: support monotonic time without RTC

Use the Timer session duration for CLOCK_MONOTONIC and  CLOCK_UPTIME.
Use the Genode::Duration object for passing internal time, it supports
sub-millisecond time and helps disambiguate units of time.

Fix #3018

repos/libports/src/lib/libc/task.cc

@@ -217,9 +217,9 @@ struct Libc::Timer
 
 	Timer(Genode::Env &env) : _timer(env) { }
 
-	unsigned long curr_time()
+	Genode::Duration curr_time()
 	{
-		return _timer.curr_time().trunc_to_plain_us().value/1000;
+		return _timer.curr_time();
 	}
 
 	static Microseconds microseconds(unsigned long timeout_ms)
@@ -281,22 +281,22 @@ struct Libc::Timeout
 
 	void start(unsigned long timeout_ms)
 	{
-		unsigned long const now = _timer_accessor.timer().curr_time();
+		Milliseconds const now = _timer_accessor.timer().curr_time().trunc_to_plain_ms();
 
 		_expired             = false;
-		_absolute_timeout_ms = now + timeout_ms;
+		_absolute_timeout_ms = now.value + timeout_ms;
 
 		_timeout.schedule(_timer_accessor.timer().microseconds(timeout_ms));
 	}
 
 	unsigned long duration_left() const
 	{
-		unsigned long const now = _timer_accessor.timer().curr_time();
+		Milliseconds const now = _timer_accessor.timer().curr_time().trunc_to_plain_ms();
 
-		if (_expired || _absolute_timeout_ms < now)
+		if (_expired || _absolute_timeout_ms < now.value)
 			return 0;
 
-		return _absolute_timeout_ms - now;
+		return _absolute_timeout_ms - now.value;
 	}
 };
 
@@ -751,7 +751,7 @@ struct Libc::Kernel
 			}
 		}
 
-		unsigned long current_time()
+		Genode::Duration current_time()
 		{
 			return _timer_accessor.timer().curr_time();
 		}
@@ -889,7 +889,7 @@ void Libc::dispatch_pending_io_signals()
 }
 
 
-unsigned long Libc::current_time()
+Genode::Duration Libc::current_time()
 {
 	return kernel->current_time();
 }

repos/libports/src/lib/libc/task.h

@@ -21,6 +21,7 @@
 #ifndef _LIBC__TASK_H_
 #define _LIBC__TASK_H_
 
+#include <os/duration.h>
 #include <util/xml_node.h>
 
 namespace Libc {
@@ -53,7 +54,7 @@ namespace Libc {
 	/**
 	 * Get time since startup in ms
 	 */
-	unsigned long current_time();
+	Genode::Duration current_time();
 
 	/**
 	 * Suspend main user context and the component entrypoint

repos/libports/src/lib/libc/time.cc

@@ -24,32 +24,54 @@ namespace Libc { time_t read_rtc(); }
 extern "C" __attribute__((weak))
 int clock_gettime(clockid_t clk_id, struct timespec *ts)
 {
-	if (!ts) return 0;
-
-	static bool   initial_rtc_requested = false;
-	static time_t initial_rtc = 0;
-	static unsigned long t0 = 0;
+	if (!ts) return Libc::Errno(EFAULT);
 
+	/* initialize timespec just in case users do not check for errors */
 	ts->tv_sec  = 0;
 	ts->tv_nsec = 0;
 
-	/* try to read rtc once */
-	if (!initial_rtc_requested) {
-		initial_rtc_requested = true;
+	switch (clk_id) {
 
-		initial_rtc = Libc::read_rtc();
+	/* IRL wall-time */
+	case CLOCK_REALTIME:
+	case CLOCK_SECOND: /* FreeBSD specific */
+	{
+		static bool   initial_rtc_requested = false;
+		static time_t initial_rtc = 0;
+		static unsigned long t0_ms = 0;
 
-		if (initial_rtc)
-			t0 = Libc::current_time();
+		/* try to read rtc once */
+		if (!initial_rtc_requested) {
+			initial_rtc_requested = true;
+			initial_rtc = Libc::read_rtc();
+			if (initial_rtc) {
+				t0_ms = Libc::current_time().trunc_to_plain_ms().value;
+			}
+		}
+
+		if (!initial_rtc) return Libc::Errno(EINVAL);
+
+		unsigned long time = Libc::current_time().trunc_to_plain_ms().value - t0_ms;
+
+		ts->tv_sec  = initial_rtc + time/1000;
+		ts->tv_nsec = (time % 1000) * (1000*1000);
+		break;
 	}
 
-	if (!initial_rtc)
+	/* component uptime */
+	case CLOCK_MONOTONIC:
+	case CLOCK_UPTIME:
+	{
+		unsigned long us = Libc::current_time().trunc_to_plain_us().value;
+
+		ts->tv_sec  = us / (1000*1000);
+		ts->tv_nsec = (us % (1000*1000)) * 1000;
+		break;
+	}
+
+	default:
 		return Libc::Errno(EINVAL);
-
-	unsigned long time = Libc::current_time() - t0;
-
-	ts->tv_sec  = initial_rtc + time/1000;
-	ts->tv_nsec = (time % 1000) * (1000*1000);
+	}
 
 	return 0;
 }
@@ -62,7 +84,7 @@ int gettimeofday(struct timeval *tv, struct timezone *)
 
 	struct timespec ts;
 
-	if (int ret = clock_gettime(0, &ts))
+	if (int ret = clock_gettime(CLOCK_REALTIME, &ts))
 		return ret;
 
 	tv->tv_sec  = ts.tv_sec;