[PATCH 1/2] core: add nm_utils_monotonic_timestamp_as_boottime() function

[Mathieu Trudel-Lapierre <mathieu trudel-lapierre canonical com>]

From: Thomas Haller <thaller redhat com>

---
 src/NetworkManagerUtils.c | 52 ++++++++++++++++++++++++++++++++++++++++++++---
 src/NetworkManagerUtils.h |  1 +
 2 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/src/NetworkManagerUtils.c b/src/NetworkManagerUtils.c
index 82d695c..ba8041d 100644
--- a/src/NetworkManagerUtils.c
+++ b/src/NetworkManagerUtils.c
@@ -1782,12 +1782,12 @@ nm_utils_cmp_connection_by_autoconnect_priority (NMConnection **a, NMConnection
 /**************************************************************************/
 
 static gint64 monotonic_timestamp_offset_sec;
+static gboolean monotonic_timestamp_initialized = FALSE;
 
 static void
 monotonic_timestamp_get (struct timespec *tp)
 {
        static int clock_mode = 0;
-       gboolean first_time = FALSE;
        int err = 0;
 
        switch (clock_mode) {
@@ -1799,7 +1799,7 @@ monotonic_timestamp_get (struct timespec *tp)
                        err = clock_gettime (CLOCK_MONOTONIC, tp);
                } else
                        clock_mode = 1;
-               first_time = TRUE;
+               monotonic_timestamp_initialized = FALSE;
                break;
        case 1:
                /* default, return CLOCK_BOOTTIME */
@@ -1815,7 +1815,7 @@ monotonic_timestamp_get (struct timespec *tp)
        g_assert (err == 0); (void)err;
        g_assert (tp->tv_nsec >= 0 && tp->tv_nsec < NM_UTILS_NS_PER_SECOND);
 
-       if (G_LIKELY (!first_time))
+       if (G_LIKELY (monotonic_timestamp_initialized))
                return;
 
        /* Calculate an offset for the time stamp.
@@ -1832,6 +1832,7 @@ monotonic_timestamp_get (struct timespec *tp)
         * wraps (~68 years).
         **/
        monotonic_timestamp_offset_sec = (- ((gint64) tp->tv_sec)) + 1;
+       monotonic_timestamp_initialized = TRUE;
 
        if (nm_logging_enabled (LOGL_DEBUG, LOGD_CORE)) {
                time_t now = time (NULL);
@@ -2196,6 +2197,51 @@ out:
        g_array_free (sorted_hashes, TRUE);
 }
 
+/**
+ * nm_utils_monotonic_timestamp_as_boottime:
+ * @timestamp: the monotonic-timestamp that should be converted into CLOCK_BOOTTIME.
+ * @timestamp_ns_per_tick: How many nano seconds make one unit of @timestamp? E.g. if
+ * @timestamp is in unit seconds, pass %NM_UTILS_NS_PER_SECOND; @timestamp in nano
+ * seconds, pass 1; @timestamp in milli seconds, pass %NM_UTILS_NS_PER_SECOND/1000; etc.
+ *
+ * Returns: the monotonic-timestamp as CLOCK_BOOTTIME, as returned by clock_gettime().
+ * The unit is the same as the passed in @timestamp basd on @timestamp_ns_per_tick.
+ * E.g. if you passed @timestamp in as seconds, it will return boottime in seconds.
+ * If @timestamp is a non-positive, it returns -1. Note that a (valid) monotonic-timestamp
+ * is always positive.
+ **/
+gint64
+nm_utils_monotonic_timestamp_as_boottime (gint64 timestamp, gint64 timestamp_ns_per_tick)
+{
+       gint64 offset;
+
+       /* only support ns-per-tick being a multiple of 10. */
+       g_return_val_if_fail (timestamp_ns_per_tick == 1
+                             || (timestamp_ns_per_tick > 0 &&
+                                 timestamp_ns_per_tick <= NM_UTILS_NS_PER_SECOND &&
+                                 timestamp_ns_per_tick % 10 == 0),
+                             -1);
+
+       /* Check that the timestamp is in a valid range. */
+       g_return_val_if_fail (timestamp >= 0, -1);
+
+       /* timestamp == 0 is not a valid timestamp. Treat it special and return -1. */
+       if (timestamp <= 0)
+               return -1;
+
+       /* if the caller didn't yet ever fetch a monotonic-timestamp, he cannot pass any meaningful
+        * value (because he has no idea what these timestamps would be). That would be a bug. */
+       g_return_val_if_fail (G_LIKELY (monotonic_timestamp_initialized), -1);
+
+       /* calculate the offset of monotonic-timestamp to boottime. offset_s is <= 1. */
+       offset = monotonic_timestamp_offset_sec * (NM_UTILS_NS_PER_SECOND / timestamp_ns_per_tick);
+
+       /* check for overflow. */
+       g_return_val_if_fail (offset>0 || timestamp < G_MAXINT64 + offset, G_MAXINT64);
+
+       return timestamp - offset;
+}
+
 
 #define IPV6_PROPERTY_DIR "/proc/sys/net/ipv6/conf/"
 #define IPV4_PROPERTY_DIR "/proc/sys/net/ipv4/conf/"
diff --git a/src/NetworkManagerUtils.h b/src/NetworkManagerUtils.h
index 99de3b6..16c5ba3 100644
--- a/src/NetworkManagerUtils.h
+++ b/src/NetworkManagerUtils.h
@@ -141,6 +141,7 @@ gint64 nm_utils_get_monotonic_timestamp_ns (void);
 gint64 nm_utils_get_monotonic_timestamp_us (void);
 gint64 nm_utils_get_monotonic_timestamp_ms (void);
 gint32 nm_utils_get_monotonic_timestamp_s (void);
+gint64 nm_utils_monotonic_timestamp_as_boottime (gint64 timestamp, gint64 timestamp_ticks_per_ns);
 
 const char *ASSERT_VALID_PATH_COMPONENT (const char *name) G_GNUC_WARN_UNUSED_RESULT;
 const char *nm_utils_ip6_property_path (const char *ifname, const char *property);
-- 
2.1.4