sd-event: allow sd_event_source_is_enabled() to return false for NULL

This is a natural use case, and instead of defining a wrapper to do this
for us, let's just make this part of the API. Calling with NULL was not
allowed, so this is not a breaking change to the interface.

(After sd_event_source_is_enabled was originally added, we introduced
sd_event_source_disable_unref() and other similar functions which accept
NULL. So not accepting NULL here is likely to confuse people. Let's just
make the API usable with minimal fuss.)

man/sd_event_source_set_enabled.xml

@@ -68,13 +68,15 @@
     loop wakeups and will not be dispatched, until they are enabled
     again.</para>
 
-    <para><function>sd_event_source_get_enabled()</function> may be
-    used to query whether the event source object
-    <parameter>source</parameter> is currently enabled or not. It
-    returns the enablement state (one of <constant>SD_EVENT_ON</constant>,
-    <constant>SD_EVENT_OFF</constant>, <constant>SD_EVENT_ONESHOT</constant>)
-    in <parameter>enabled</parameter>, if it is not <constant>NULL</constant>.
-    It also returns true if the event source is not disabled.</para>
+    <para><function>sd_event_source_get_enabled()</function> may be used to query whether the event source
+    object <parameter>source</parameter> is currently enabled or not. If both the
+    <parameter>source</parameter> and the output parameter <parameter>enabled</parameter> are
+    <constant>NULL</constant>, this function returns false. Otherwise, <parameter>source</parameter> must be
+    a valid pointer to an <structname>sd_event_source</structname> object. If the output parameter
+    <parameter>enabled</parameter> is not <constant>NULL</constant>, it is set to the enablement state (one
+    of <constant>SD_EVENT_ON</constant>, <constant>SD_EVENT_OFF</constant>,
+    <constant>SD_EVENT_ONESHOT</constant>). The function also returns true if the event source is not
+    disabled.</para>
 
     <para>Event source objects are enabled when they are first created
     with calls such as

src/journal/managed-journal-file.c

@@ -375,12 +375,9 @@ ManagedJournalFile* managed_journal_file_close(ManagedJournalFile *f) {
         }
 #endif
 
-        if (f->file->post_change_timer) {
-                if (sd_event_source_get_enabled(f->file->post_change_timer, NULL) > 0)
-                        journal_file_post_change(f->file);
-
-                sd_event_source_disable_unref(f->file->post_change_timer);
-        }
+        if (sd_event_source_get_enabled(f->file->post_change_timer, NULL) > 0)
+                journal_file_post_change(f->file);
+        sd_event_source_disable_unref(f->file->post_change_timer);
 
         managed_journal_file_set_offline(f, true);
 

src/libsystemd/sd-event/event-util.c

@@ -116,13 +116,6 @@ int event_source_disable(sd_event_source *s) {
         return sd_event_source_set_enabled(s, SD_EVENT_OFF);
 }
 
-int event_source_is_enabled(sd_event_source *s) {
-        if (!s)
-                return false;
-
-        return sd_event_source_get_enabled(s, NULL);
-}
-
 int event_add_time_change(sd_event *e, sd_event_source **ret, sd_event_io_handler_t callback, void *userdata) {
         _cleanup_(sd_event_source_unrefp) sd_event_source *s = NULL;
         _cleanup_close_ int fd = -1;

src/libsystemd/sd-event/event-util.h

@@ -28,6 +28,5 @@ int event_reset_time_relative(
                 const char *description,
                 bool force_reset);
 int event_source_disable(sd_event_source *s);
-int event_source_is_enabled(sd_event_source *s);
 
 int event_add_time_change(sd_event *e, sd_event_source **ret, sd_event_io_handler_t callback, void *userdata);

src/libsystemd/sd-event/sd-event.c

@@ -2413,6 +2413,10 @@ fail:
 }
 
 _public_ int sd_event_source_get_enabled(sd_event_source *s, int *ret) {
+        /* Quick mode: the event source doesn't exist and we only want to query boolean enablement state. */
+        if (!s && !ret)
+                return false;
+
         assert_return(s, -EINVAL);
         assert_return(!event_pid_changed(s->event), -ECHILD);
 

src/network/netdev/wireguard.c

@@ -405,7 +405,7 @@ static int peer_resolve_endpoint(WireguardPeer *peer) {
                 /* Not necessary to resolve the endpoint. */
                 return 0;
 
-        if (event_source_is_enabled(peer->resolve_retry_event_source) > 0)
+        if (sd_event_source_get_enabled(peer->resolve_retry_event_source, NULL) > 0)
                 /* Timer event source is enabled. The endpoint will be resolved later. */
                 return 0;