logind: fix Display property of user objects

When we dropped support for creating a per-user to the "main" X11
display we stopped returning useful data in the "Display" user property.
With this change this is fixed and we again expose an appropriate
(graphical session) in the property that is useful as the "main" one, if
one is needed.

5 files changed, 47 insertions, 3 deletions

diff --git a/src/login/logind-session.c b/src/login/logind-session.c
index 4fb229e354..9a54101301 100644
--- a/src/login/logind-session.c
+++ b/src/login/logind-session.c
@@ -545,6 +545,8 @@ int session_start(Session *s) {
 
         s->started = true;
 
+        user_elect_display(s->user);
+
         /* Save data */
         session_save(s);
         user_save(s->user);
@@ -553,7 +555,7 @@ int session_start(Session *s) {
 
         /* Send signals */
         session_send_signal(s, true);
-        user_send_changed(s->user, "Sessions", NULL);
+        user_send_changed(s->user, "Sessions", "Display", NULL);
         if (s->seat) {
                 if (s->seat->active == s)
                         seat_send_changed(s->seat, "Sessions", "ActiveSession", NULL);
@@ -612,6 +614,8 @@ int session_stop(Session *s, bool force) {
 
         s->stopping = true;
 
+        user_elect_display(s->user);
+
         session_save(s);
         user_save(s->user);
 
@@ -660,7 +664,7 @@ int session_finalize(Session *s) {
         }
 
         user_save(s->user);
-        user_send_changed(s->user, "Sessions", NULL);
+        user_send_changed(s->user, "Sessions", "Display", NULL);
 
         return r;
 }
diff --git a/src/login/logind-session.h b/src/login/logind-session.h
index f78f30956d..81957dfa78 100644
--- a/src/login/logind-session.h
+++ b/src/login/logind-session.h
@@ -60,6 +60,8 @@ typedef enum SessionType {
         _SESSION_TYPE_INVALID = -1
 } SessionType;
 
+#define SESSION_TYPE_IS_GRAPHICAL(type) IN_SET(type, SESSION_X11, SESSION_WAYLAND, SESSION_MIR)
+
 enum KillWho {
         KILL_LEADER,
         KILL_ALL,
diff --git a/src/login/logind-user-dbus.c b/src/login/logind-user-dbus.c
index 6266ccb0f0..51793f6dad 100644
--- a/src/login/logind-user-dbus.c
+++ b/src/login/logind-user-dbus.c
@@ -220,7 +220,7 @@ const sd_bus_vtable user_vtable[] = {
         SD_BUS_PROPERTY("RuntimePath", "s", NULL, offsetof(User, runtime_path), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Service", "s", NULL, offsetof(User, service), SD_BUS_VTABLE_PROPERTY_CONST),
         SD_BUS_PROPERTY("Slice", "s", NULL, offsetof(User, slice), SD_BUS_VTABLE_PROPERTY_CONST),
-        SD_BUS_PROPERTY("Display", "(so)", property_get_display, 0, SD_BUS_VTABLE_PROPERTY_CONST),
+        SD_BUS_PROPERTY("Display", "(so)", property_get_display, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("State", "s", property_get_state, 0, 0),
         SD_BUS_PROPERTY("Sessions", "a(so)", property_get_sessions, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
         SD_BUS_PROPERTY("IdleHint", "b", property_get_idle_hint, 0, SD_BUS_VTABLE_PROPERTY_EMITS_CHANGE),
diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index 5fffa651a3..fdbccb364c 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -713,6 +713,43 @@ int user_kill(User *u, int signo) {
         return manager_kill_unit(u->manager, u->slice, KILL_ALL, signo, NULL);
 }
 
+void user_elect_display(User *u) {
+        Session *graphical = NULL, *text = NULL, *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. */
+
+        LIST_FOREACH(sessions_by_user, s, u->sessions) {
+
+                if (s->class != SESSION_USER)
+                        continue;
+
+                if (s->stopping)
+                        continue;
+
+                if (SESSION_TYPE_IS_GRAPHICAL(s->type))
+                        graphical = s;
+                else
+                        text = s;
+        }
+
+        if (graphical &&
+            (!u->display ||
+             u->display->class != SESSION_USER ||
+             u->display->stopping ||
+             !SESSION_TYPE_IS_GRAPHICAL(u->display->type)))
+                u->display = graphical;
+
+        if (text &&
+            (!u->display ||
+             u->display->class != SESSION_USER ||
+             u->display->stopping))
+                u->display = text;
+}
+
 static const char* const user_state_table[_USER_STATE_MAX] = {
         [USER_OFFLINE] = "offline",
         [USER_OPENING] = "opening",
diff --git a/src/login/logind-user.h b/src/login/logind-user.h
index f237d2a6b9..4e0568fea9 100644
--- a/src/login/logind-user.h
+++ b/src/login/logind-user.h
@@ -80,6 +80,7 @@ int user_save(User *u);
 int user_load(User *u);
 int user_kill(User *u, int signo);
 int user_check_linger_file(User *u);
+void user_elect_display(User *u);
 
 extern const sd_bus_vtable user_vtable[];
 int user_node_enumerator(sd_bus *bus, const char *path, void *userdata, char ***nodes, sd_bus_error *error);