+static int get_seat_from_display(const char *display, const char **seat, uint32_t *vtnr) {
+ char *p = NULL;
+ int r;
+ int fd;
+ union sockaddr_union sa;
+ struct ucred ucred;
+ socklen_t l;
+ char *tty;
+ int v;
+
+ assert(display);
+ assert(seat);
+ assert(vtnr);
+
+ /* We deduce the X11 socket from the display name, then use
+ * SO_PEERCRED to determine the X11 server process, ask for
+ * the controlling tty of that and if it's a VC then we know
+ * the seat and the virtual terminal. Sounds ugly, is only
+ * semi-ugly. */
+
+ r = socket_from_display(display, &p);
+ if (r < 0)
+ return r;
+
+ fd = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+ if (fd < 0) {
+ free(p);
+ return -errno;
+ }
+
+ zero(sa);
+ sa.un.sun_family = AF_UNIX;
+ strncpy(sa.un.sun_path, p, sizeof(sa.un.sun_path)-1);
+ free(p);
+
+ if (connect(fd, &sa.sa, offsetof(struct sockaddr_un, sun_path) + strlen(sa.un.sun_path)) < 0) {
+ close_nointr_nofail(fd);
+ return -errno;
+ }
+
+ l = sizeof(ucred);
+ r = getsockopt(fd, SOL_SOCKET, SO_PEERCRED, &ucred, &l);
+ close_nointr_nofail(fd);
+
+ if (r < 0)
+ return -errno;
+
+ r = get_ctty(ucred.pid, NULL, &tty);
+ if (r < 0)
+ return r;
+
+ v = vtnr_from_tty(tty);
+ free(tty);
+
+ if (v < 0)
+ return v;
+ else if (v == 0)
+ return -ENOENT;
+
+ *seat = "seat0";
+ *vtnr = (uint32_t) v;
+
+ return 0;
+}
+