+#else
+ Session *s;
+ int res = 0;
+
+ assert(u);
+
+ LIST_FOREACH(sessions_by_user, s, u->sessions) {
+ int r = session_kill(s, KILL_ALL, signo);
+ if (res == 0 && r < 0)
+ res = r;
+ }
+
+ return res;
+#endif // 0
+}
+
+static bool elect_display_filter(Session *s) {
+ /* Return true if the session is a candidate for the user’s ‘primary
+ * session’ or ‘display’. */
+ assert(s);
+
+ return (s->class == SESSION_USER && !s->stopping);
+}
+
+static int elect_display_compare(Session *s1, Session *s2) {
+ /* Indexed by SessionType. Lower numbers mean more preferred. */
+ const int type_ranks[_SESSION_TYPE_MAX] = {
+ [SESSION_UNSPECIFIED] = 0,
+ [SESSION_TTY] = -2,
+ [SESSION_X11] = -3,
+ [SESSION_WAYLAND] = -3,
+ [SESSION_MIR] = -3,
+ [SESSION_WEB] = -1,
+ };
+
+ /* Calculate the partial order relationship between s1 and s2,
+ * returning < 0 if s1 is preferred as the user’s ‘primary session’,
+ * 0 if s1 and s2 are equally preferred or incomparable, or > 0 if s2
+ * is preferred.
+ *
+ * s1 or s2 may be NULL. */
+ if (!s1 && !s2)
+ return 0;
+
+ if ((s1 == NULL) != (s2 == NULL))
+ return (s1 == NULL) - (s2 == NULL);
+
+ if (s1->stopping != s2->stopping)
+ return s1->stopping - s2->stopping;
+
+ if ((s1->class != SESSION_USER) != (s2->class != SESSION_USER))
+ return (s1->class != SESSION_USER) - (s2->class != SESSION_USER);
+
+ if ((s1->type == _SESSION_TYPE_INVALID) != (s2->type == _SESSION_TYPE_INVALID))
+ return (s1->type == _SESSION_TYPE_INVALID) - (s2->type == _SESSION_TYPE_INVALID);
+
+ if (s1->type != s2->type)
+ return type_ranks[s1->type] - type_ranks[s2->type];
+
+ return 0;
+}
+
+void user_elect_display(User *u) {
+ Session *s;
+
+ assert(u);
+
+ /* This elects a primary session for each user, which we call
+ * the "display". We try to keep the assignment stable, but we
+ * "upgrade" to better choices. */
+ log_debug("Electing new display for user %s", u->name);
+
+ LIST_FOREACH(sessions_by_user, s, u->sessions) {
+ if (!elect_display_filter(s)) {
+ log_debug("Ignoring session %s", s->id);
+ continue;
+ }
+
+ if (elect_display_compare(s, u->display) < 0) {
+ log_debug("Choosing session %s in preference to %s", s->id, u->display ? u->display->id : "-");
+ u->display = s;
+ }
+ }