+ 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;
+ }
+ }