sd-login: add sd_session_get_leader interface

src/libsystemd/libsystemd.sym

@@ -826,4 +826,5 @@ global:
         sd_pid_notify_barrier;
         sd_event_source_leave_ratelimit;
         sd_journal_step_one;
+        sd_session_get_leader;
 } LIBSYSTEMD_253;

src/libsystemd/sd-login/sd-login.c

@@ -870,6 +870,25 @@ _public_ int sd_session_get_remote_host(const char *session, char **remote_host)
         return session_get_string(session, "REMOTE_HOST", remote_host);
 }
 
+_public_ int sd_session_get_leader(const char *session, pid_t *leader) {
+        _cleanup_free_ char *leader_string = NULL;
+        pid_t pid;
+        int r;
+
+        assert_return(leader, -EINVAL);
+
+        r = session_get_string(session, "LEADER", &leader_string);
+        if (r < 0)
+                return r;
+
+        r = parse_pid(leader_string, &pid);
+        if (r < 0)
+                return r;
+
+        *leader = pid;
+        return 0;
+}
+
 _public_ int sd_seat_get_active(const char *seat, char **session, uid_t *uid) {
         _cleanup_free_ char *p = NULL, *s = NULL, *t = NULL;
         int r;

src/systemd/sd-login.h

@@ -184,6 +184,9 @@ int sd_session_get_desktop(const char *session, char **desktop);
 /* Determine the X11 display of this session. */
 int sd_session_get_display(const char *session, char **display);
 
+/* Determine the leader process of this session. */
+int sd_session_get_leader(const char *session, pid_t *leader);
+
 /* Determine the remote host of this session. */
 int sd_session_get_remote_host(const char *session, char **remote_host);