sd-event: check clock argument to sd_event_now()

sd_event_now() is a public function, so we must check all
arguments for validity. Update man page and add tests.

Sample debug message:
Assertion 'IN_SET(clock, CLOCK_REALTIME, CLOCK_REALTIME_ALARM, CLOCK_MONOTONIC, CLOCK_BOOTTIME, CLOCK_BOOTTIME_ALARM)' failed at src/libsystemd/sd-event/sd-event.c:2719, function sd_event_now(). Ignoring.

1 files changed, 7 insertions, 2 deletions

diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index aeb06ad9a8..c898ccc3c6 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -2751,6 +2751,12 @@ _public_ int sd_event_now(sd_event *e, clockid_t clock, uint64_t *usec) {
         assert_return(e, -EINVAL);
         assert_return(usec, -EINVAL);
         assert_return(!event_pid_changed(e), -ECHILD);
+        assert_return(IN_SET(clock,
+                             CLOCK_REALTIME,
+                             CLOCK_REALTIME_ALARM,
+                             CLOCK_MONOTONIC,
+                             CLOCK_BOOTTIME,
+                             CLOCK_BOOTTIME_ALARM), -EOPNOTSUPP);
 
         if (!dual_timestamp_is_set(&e->timestamp)) {
                 /* Implicitly fall back to now() if we never ran
@@ -2770,8 +2776,7 @@ _public_ int sd_event_now(sd_event *e, clockid_t clock, uint64_t *usec) {
                 *usec = e->timestamp.monotonic;
                 break;
 
-        case CLOCK_BOOTTIME:
-        case CLOCK_BOOTTIME_ALARM:
+        default:
                 *usec = e->timestamp_boottime;
                 break;
         }