sd-event: introduce sd_event_source_get_inotify_path()

This may be useful when there are multiple inotify event sources exist.
Without this, users need to manage the event sources and paths.

src/libsystemd/libsystemd.sym

@@ -840,4 +840,5 @@ global:
         sd_bus_creds_get_pidfd_dup;
         sd_bus_creds_new_from_pidfd;
         sd_journal_stream_fd_with_namespace;
+        sd_event_source_get_inotify_path;
 } LIBSYSTEMD_255;

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

@@ -3292,6 +3292,18 @@ _public_ int sd_event_source_get_inotify_mask(sd_event_source *s, uint32_t *ret)
         return 0;
 }
 
+_public_ int sd_event_source_get_inotify_path(sd_event_source *s, char **ret) {
+        assert_return(s, -EINVAL);
+        assert_return(ret, -EINVAL);
+        assert_return(s->type == SOURCE_INOTIFY, -EDOM);
+        assert_return(!event_origin_changed(s->event), -ECHILD);
+
+        if (!s->inotify.inode_data || s->inotify.inode_data->fd < 0)
+                return -ESTALE;
+
+        return fd_get_path(s->inotify.inode_data->fd, ret);
+}
+
 _public_ int sd_event_source_set_prepare(sd_event_source *s, sd_event_handler_t callback) {
         int r;
 

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

@@ -475,6 +475,7 @@ static int delete_self_handler(sd_event_source *s, const struct inotify_event *e
 
 static void test_inotify_one(unsigned n_create_events) {
         _cleanup_(rm_rf_physical_and_freep) char *p = NULL;
+        _cleanup_free_ char *pp = NULL;
         sd_event_source *a = NULL, *b = NULL, *c = NULL, *d = NULL;
         struct inotify_context context = {
                 .n_create_events = n_create_events,
@@ -500,6 +501,16 @@ static void test_inotify_one(unsigned n_create_events) {
         assert_se(sd_event_source_set_description(b, "1") >= 0);
         assert_se(sd_event_source_set_description(c, "2") >= 0);
 
+        assert_se(sd_event_source_get_inotify_path(a, &pp) >= 0);
+        assert_se(path_equal_or_inode_same(pp, p, 0));
+        pp = mfree(pp);
+        assert_se(sd_event_source_get_inotify_path(b, &pp) >= 0);
+        assert_se(path_equal_or_inode_same(pp, p, 0));
+        pp = mfree(pp);
+        assert_se(sd_event_source_get_inotify_path(b, &pp) >= 0);
+        assert_se(path_equal_or_inode_same(pp, p, 0));
+        pp = mfree(pp);
+
         q = strjoina(p, "/sub");
         assert_se(touch(q) >= 0);
         assert_se(sd_event_add_inotify(e, &d, q, IN_DELETE_SELF, delete_self_handler, &context) >= 0);

src/systemd/sd-event.h

@@ -161,6 +161,7 @@ int sd_event_source_send_child_signal(sd_event_source *s, int sig, const siginfo
 int sd_event_source_send_child_signal(sd_event_source *s, int sig, const void *si, unsigned flags);
 #endif
 int sd_event_source_get_inotify_mask(sd_event_source *s, uint32_t *ret);
+int sd_event_source_get_inotify_path(sd_event_source *s, char **ret);
 int sd_event_source_set_memory_pressure_type(sd_event_source *e, const char *ty);
 int sd_event_source_set_memory_pressure_period(sd_event_source *s, uint64_t threshold_usec, uint64_t window_usec);
 int sd_event_source_set_destroy_callback(sd_event_source *s, sd_event_destroy_t callback);