sd-event: add relative timer calls

We frequently want to set a timer relative to the current time. Let's
add an explicit API for this. This not only saves us a few lines of code
everywhere and simplifies things, but also allows us to do correct
overflow checking.

2 files changed, 48 insertions, 0 deletions

diff --git a/src/libsystemd/libsystemd.sym b/src/libsystemd/libsystemd.sym
index 1e654b49ea..3168a4dcc4 100644
--- a/src/libsystemd/libsystemd.sym
+++ b/src/libsystemd/libsystemd.sym
@@ -721,3 +721,9 @@ global:
         sd_journal_enumerate_available_data;
         sd_journal_enumerate_available_unique;
 } LIBSYSTEMD_245;
+
+LIBSYSTEMD_247 {
+global:
+        sd_event_add_time_relative;
+        sd_event_source_set_time_relative;
+} LIBSYSTEMD_246;
diff --git a/src/libsystemd/sd-event/sd-event.c b/src/libsystemd/sd-event/sd-event.c
index 860eb048ff..8b338f5db6 100644
--- a/src/libsystemd/sd-event/sd-event.c
+++ b/src/libsystemd/sd-event/sd-event.c
@@ -1146,6 +1146,31 @@ _public_ int sd_event_add_time(
         return 0;
 }
 
+_public_ int sd_event_add_time_relative(
+                sd_event *e,
+                sd_event_source **ret,
+                clockid_t clock,
+                uint64_t usec,
+                uint64_t accuracy,
+                sd_event_time_handler_t callback,
+                void *userdata) {
+
+        usec_t t;
+        int r;
+
+        /* Same as sd_event_add_time() but operates relative to the event loop's current point in time, and
+         * checks for overflow. */
+
+        r = sd_event_now(e, clock, &t);
+        if (r < 0)
+                return r;
+
+        if (usec >= USEC_INFINITY - t)
+                return -EOVERFLOW;
+
+        return sd_event_add_time(e, ret, clock, t + usec, accuracy, callback, userdata);
+}
+
 static int signal_exit_callback(sd_event_source *s, const struct signalfd_siginfo *si, void *userdata) {
         assert(s);
 
@@ -2402,6 +2427,23 @@ _public_ int sd_event_source_set_time(sd_event_source *s, uint64_t usec) {
         return 0;
 }
 
+_public_ int sd_event_source_set_time_relative(sd_event_source *s, uint64_t usec) {
+        usec_t t;
+        int r;
+
+        assert_return(s, -EINVAL);
+        assert_return(EVENT_SOURCE_IS_TIME(s->type), -EDOM);
+
+        r = sd_event_now(s->event, event_source_type_to_clock(s->type), &t);
+        if (r < 0)
+                return r;
+
+        if (usec >= USEC_INFINITY - t)
+                return -EOVERFLOW;
+
+        return sd_event_source_set_time(s, t + usec);
+}
+
 _public_ int sd_event_source_get_time_accuracy(sd_event_source *s, uint64_t *usec) {
         assert_return(s, -EINVAL);
         assert_return(usec, -EINVAL);