sd-login: add sd_session_get_start_time

src/libsystemd/libsystemd.sym

@@ -816,4 +816,5 @@ global:
 LIBSYSTEMD_254 {
 global:
         sd_session_get_username;
+        sd_session_get_start_time;
 } LIBSYSTEMD_253;

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

@@ -750,6 +750,33 @@ _public_ int sd_session_get_seat(const char *session, char **seat) {
         return session_get_string(session, "SEAT", seat);
 }
 
+_public_ int sd_session_get_start_time(const char *session, uint64_t *usec) {
+        _cleanup_free_ char *p = NULL, *s = NULL;
+        usec_t t;
+        int r;
+
+        assert_return(usec, -EINVAL);
+
+        r = file_of_session(session, &p);
+        if (r < 0)
+                return r;
+
+        r = parse_env_file(NULL, p, "REALTIME", &s);
+        if (r == -ENOENT)
+                return -ENXIO;
+        if (r < 0)
+                return r;
+        if (isempty(s))
+                return -EIO;
+
+        r = safe_atou64(s, &t);
+        if (r < 0)
+                return r;
+
+        *usec = t;
+        return 0;
+}
+
 _public_ int sd_session_get_tty(const char *session, char **tty) {
         return session_get_string(session, "TTY", tty);
 }