timer: Introduce osmo_clock_gettime to override clock_gettime

Change-Id: I5bebc6e01fc9d238065bc2517058f0ba85620349

3 files changed, 141 insertions, 2 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 3d6e6f79..2641a975 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -13,7 +13,8 @@ endif
 lib_LTLIBRARIES = libosmocore.la
 
 libosmocore_la_LIBADD = $(BACKTRACE_LIB) $(TALLOC_LIBS)
-libosmocore_la_SOURCES = timer.c timer_gettimeofday.c select.c signal.c msgb.c bits.c \
+libosmocore_la_SOURCES = timer.c timer_gettimeofday.c timer_clockgettime.c \
+			 select.c signal.c msgb.c bits.c \
 			 bitvec.c bitcomp.c counter.c fsm.c \
 			 write_queue.c utils.c socket.c \
 			 logging.c logging_syslog.c logging_gsmtap.c rate_ctr.c \
diff --git a/src/timer_clockgettime.c b/src/timer_clockgettime.c
new file mode 100644
index 00000000..8d9760c5
--- /dev/null
+++ b/src/timer_clockgettime.c
@@ -0,0 +1,138 @@
+/*
+ * (C) 2016 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved
+ *
+ * Authors: Pau Espin Pedrol <pespin@sysmocom.de>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+/*! \addtogroup timer
+ *  @{
+ * \file timer_clockgettime.c
+ * Overriding Time: osmo_clock_gettime()
+ *      - Useful to write and reproduce tests that depend on specific time
+ *        factors. This API allows to fake the timespec provided by `clock_gettime()`
+ *        by using a small shim osmo_clock_gettime().
+ *      - Choose the clock you want to override, for instance CLOCK_MONOTONIC.
+ *      - If the clock override is disabled (default) for a given clock,
+ *        osmo_clock_gettime() will do the same as regular `clock_gettime()`.
+ *      - If you want osmo_clock_gettime() to provide a specific time, you must
+ *        enable time override with osmo_clock_override_enable(),
+ *        then set a pointer to the timespec storing the fake time for that
+ *        specific clock (`struct timespec *ts =
+ *        osmo_clock_override_gettimespec()`) and set it as
+ *        desired. Next time osmo_clock_gettime() is called, it will return the
+ *        values previously set through the ts pointer.
+ *      - A helper osmo_clock_override_add() is provided to increment a given
+ *        overriden clock with a specific amount of time.
+ */
+
+/*! \file timer_clockgettime.c
+ */
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <sys/time.h>
+#include <time.h>
+
+#include <osmocom/core/timer_compat.h>
+
+/*! An internal structure to handle overriden time for each clock type. */
+struct fakeclock {
+	bool override;
+	struct timespec time;
+};
+
+static struct fakeclock realtime;
+static struct fakeclock realtime_coarse;
+static struct fakeclock mono;
+static struct fakeclock mono_coarse;
+static struct fakeclock mono_raw;
+static struct fakeclock boottime;
+static struct fakeclock boottime;
+static struct fakeclock proc_cputime_id;
+static struct fakeclock th_cputime_id;
+
+static struct fakeclock* clkid_to_fakeclock(clockid_t clk_id)
+{
+	switch(clk_id) {
+	case CLOCK_REALTIME:
+		return &realtime;
+	case CLOCK_REALTIME_COARSE:
+		return &realtime_coarse;
+	case CLOCK_MONOTONIC:
+		return &mono;
+	case CLOCK_MONOTONIC_COARSE:
+		return &mono_coarse;
+	case CLOCK_MONOTONIC_RAW:
+		return &mono_raw;
+	case CLOCK_BOOTTIME:
+		return &boottime;
+	case CLOCK_PROCESS_CPUTIME_ID:
+		return &proc_cputime_id;
+	case CLOCK_THREAD_CPUTIME_ID:
+		return &th_cputime_id;
+	default:
+		return NULL;
+	}
+}
+
+/*! Shim around clock_gettime to be able to set the time manually.
+ *
+ * To override, use osmo_clock_override_enable and set the desired
+ * current time with osmo_clock_gettimespec. */
+int osmo_clock_gettime(clockid_t clk_id, struct timespec *tp)
+{
+	struct fakeclock* c = clkid_to_fakeclock(clk_id);
+	if (!c || !c->override)
+		return clock_gettime(clk_id, tp);
+
+	*tp = c->time;
+	return 0;
+}
+
+/*! Convenience function to enable or disable a specific clock fake time.
+ */
+void osmo_clock_override_enable(clockid_t clk_id, bool enable)
+{
+	struct fakeclock* c = clkid_to_fakeclock(clk_id);
+	if (c)
+		c->override = enable;
+}
+
+/*! Convenience function to return a pointer to the timespec handling the
+ * fake time for clock clk_id. */
+struct timespec *osmo_clock_override_gettimespec(clockid_t clk_id)
+{
+	struct fakeclock* c = clkid_to_fakeclock(clk_id);
+	if (c)
+		return &c->time;
+	return NULL;
+}
+
+/*! Convenience function to advance the fake time.
+ *
+ * Adds the given values to the clock time. */
+void osmo_clock_override_add(clockid_t clk_id, time_t secs, long nsecs)
+{
+	struct timespec val = { secs, nsecs };
+	struct fakeclock* c = clkid_to_fakeclock(clk_id);
+	if (c)
+		timespecadd(&c->time, &val, &c->time);
+}
+
+/*! @} */
diff --git a/src/timer_gettimeofday.c b/src/timer_gettimeofday.c
index 15b5e31d..5273a3b8 100644
--- a/src/timer_gettimeofday.c
+++ b/src/timer_gettimeofday.c
@@ -39,7 +39,7 @@ struct timeval osmo_gettimeofday_override_time = { 23, 424242 };
  * N. B: gettimeofday() is affected by discontinuous jumps in the system time
  *       (e.g., if the system administrator manually changes the system time).
  *       Hence this should NEVER be used for elapsed time computation.
- *       Instead, clock_gettime(CLOCK_MONOTONIC, ..) should be used for that (with similar shim if necessary).
+ *       Instead, osmo_clock_gettime() with CLOCK_MONOTONIC should be used for that.
  */
 int osmo_gettimeofday(struct timeval *tv, struct timezone *tz)
 {