tree-wide: don't assume CLOCK_BOOTIME is generally available

Before we invoke now(CLOCK_BOOTTIME), let's make sure we actually have that
clock, since now() will otherwise hit an assert.

Specifically, let's refuse CLOCK_BOOTTIME early in sd-event if the kernel
doesn't actually support it.

This is a follow-up for #3037, and specifically:

https://github.com/systemd/systemd/pull/3037#issuecomment-210199167

2 files changed, 17 insertions, 5 deletions

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index 79b98c293c..7ba6527f63 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -1072,6 +1072,10 @@ _public_ int sd_event_add_time(
         assert_return(e->state != SD_EVENT_FINISHED, -ESTALE);
         assert_return(!event_pid_changed(e), -ECHILD);
 
+        if (IN_SET(clock, CLOCK_BOOTTIME, CLOCK_BOOTTIME_ALARM) &&
+            !clock_boottime_supported())
+                return -EOPNOTSUPP;
+
         if (!callback)
                 callback = time_exit_callback;
 
@@ -2527,7 +2531,8 @@ _public_ int sd_event_wait(sd_event *e, uint64_t timeout) {
         }
 
         dual_timestamp_get(&e->timestamp);
-        e->timestamp_boottime = now(clock_boottime_or_monotonic());
+        if (clock_boottime_supported())
+                e->timestamp_boottime = now(CLOCK_BOOTTIME);
 
         for (i = 0; i < m; i++) {
 
@@ -2761,6 +2766,9 @@ _public_ int sd_event_now(sd_event *e, clockid_t clock, uint64_t *usec) {
                              CLOCK_BOOTTIME,
                              CLOCK_BOOTTIME_ALARM), -EOPNOTSUPP);
 
+        if (IN_SET(clock, CLOCK_BOOTTIME, CLOCK_BOOTTIME_ALARM) && !clock_boottime_supported())
+                return -EOPNOTSUPP;
+
         if (!dual_timestamp_is_set(&e->timestamp)) {
                 /* Implicitly fall back to now() if we never ran
                  * before and thus have no cached time. */
diff --git a/src/libsystemd/sd-event/test-event.c b/src/libsystemd/sd-event/test-event.c
index fd31588b8f..289114490c 100644
--- a/src/libsystemd/sd-event/test-event.c
+++ b/src/libsystemd/sd-event/test-event.c
@@ -270,8 +270,10 @@ static void test_sd_event_now(void) {
         assert_se(sd_event_now(e, CLOCK_MONOTONIC, &event_now) > 0);
         assert_se(sd_event_now(e, CLOCK_REALTIME, &event_now) > 0);
         assert_se(sd_event_now(e, CLOCK_REALTIME_ALARM, &event_now) > 0);
-        assert_se(sd_event_now(e, CLOCK_BOOTTIME, &event_now) > 0);
-        assert_se(sd_event_now(e, CLOCK_BOOTTIME_ALARM, &event_now) > 0);
+        if (clock_boottime_supported()) {
+                assert_se(sd_event_now(e, CLOCK_BOOTTIME, &event_now) > 0);
+                assert_se(sd_event_now(e, CLOCK_BOOTTIME_ALARM, &event_now) > 0);
+        }
         assert_se(sd_event_now(e, -1, &event_now) == -EOPNOTSUPP);
         assert_se(sd_event_now(e, 900 /* arbitrary big number */, &event_now) == -EOPNOTSUPP);
 
@@ -280,8 +282,10 @@ static void test_sd_event_now(void) {
         assert_se(sd_event_now(e, CLOCK_MONOTONIC, &event_now) == 0);
         assert_se(sd_event_now(e, CLOCK_REALTIME, &event_now) == 0);
         assert_se(sd_event_now(e, CLOCK_REALTIME_ALARM, &event_now) == 0);
-        assert_se(sd_event_now(e, CLOCK_BOOTTIME, &event_now) == 0);
-        assert_se(sd_event_now(e, CLOCK_BOOTTIME_ALARM, &event_now) == 0);
+        if (clock_boottime_supported()) {
+                assert_se(sd_event_now(e, CLOCK_BOOTTIME, &event_now) == 0);
+                assert_se(sd_event_now(e, CLOCK_BOOTTIME_ALARM, &event_now) == 0);
+        }
         assert_se(sd_event_now(e, -1, &event_now) == -EOPNOTSUPP);
         assert_se(sd_event_now(e, 900 /* arbitrary big number */, &event_now) == -EOPNOTSUPP);
 }