worker: reuse user's VT if availablewip/systemd-activation

When a user logs out, their session goes into the closing
state until all processes from the session exit. The X server
won't exit while the session is in the closing state, but will
instead reset itself.  When the user logs in again, we need to
select the same VT so the already running X server can properly
manage the new session.

This commit checks for the above scenario and tries to account
for it.

1 files changed, 109 insertions, 3 deletions

diff --git a/daemon/gdm-session-worker.c b/daemon/gdm-session-worker.c
index c3de1481..2277e5f0 100644
--- a/daemon/gdm-session-worker.c
+++ b/daemon/gdm-session-worker.c
@@ -52,6 +52,7 @@
 
 #ifdef WITH_SYSTEMD
 #include <systemd/sd-daemon.h>
+#include <systemd/sd-login.h>
 #endif
 
 #ifdef ENABLE_SYSTEMD_JOURNAL
@@ -1984,6 +1985,105 @@ gdm_session_worker_start_session (GdmSessionWorker  *worker,
 
 #ifdef ENABLE_WAYLAND_SUPPORT
 static gboolean
+validate_session (GdmSessionWorker *worker,
+                  const char       *session,
+                  const char       *requested_seat,
+                  const char       *requested_type,
+                  const char       *requested_state)
+{
+    int ret;
+    gboolean validated = FALSE;
+    char *state = NULL, *type = NULL, *seat = NULL;
+    uid_t uid;
+    unsigned int vt;
+
+    ret = sd_session_get_uid (session, &uid);
+
+    if (ret < 0 || uid != worker->priv->uid) {
+            goto out;
+    }
+
+    ret = sd_session_get_state (session, &state);
+
+    if (ret < 0 || state == NULL) {
+            goto out;
+    }
+
+    if (strcmp (state, requested_state) != 0) {
+            goto out;
+    }
+
+    ret = sd_session_get_type (session, &type);
+
+    if (ret < 0 || type == NULL) {
+            goto out;
+    }
+
+    if (strcmp (type, requested_type) != 0) {
+            goto out;
+    }
+
+    ret = sd_session_get_seat (session, &seat);
+
+    if (ret < 0 || seat == NULL) {
+            goto out;
+    }
+
+    if (strcmp (seat, requested_seat) != 0) {
+            goto out;
+    }
+
+    ret = sd_session_get_vt (session, &vt);
+
+    if (ret < 0 || vt <= 0) {
+            goto out;
+    }
+
+    validated = TRUE;
+
+out:
+    free (state);
+    free (type);
+    free (seat);
+    return validated;
+}
+
+static int
+find_vt_of_closing_session (GdmSessionWorker *worker)
+{
+        char **sessions = NULL;
+        unsigned int vt = 0;
+        int ret;
+        int i;
+
+        ret = sd_seat_get_sessions (worker->priv->display_seat_id, &sessions, NULL, NULL);
+
+        if (ret < 0 || sessions == NULL) {
+                goto out;
+        }
+
+        for (i = 0; sessions[i] != NULL; i++) {
+                if (vt == 0) {
+                        gboolean validated;
+                        validated = validate_session (worker, sessions[i], worker->priv->display_seat_id, "x11", "closing");
+
+                        if (validated) {
+                                ret = sd_session_get_vt (sessions[i], &vt);
+
+                                if (ret < 0) {
+                                        vt = 0;
+                                }
+                        }
+                }
+                free(sessions[i]);
+        }
+        free (sessions);
+
+out:
+        return (int) vt;
+}
+
+static gboolean
 set_up_for_new_vt (GdmSessionWorker *worker)
 {
         int fd;
@@ -2004,9 +2104,15 @@ set_up_for_new_vt (GdmSessionWorker *worker)
                 goto fail;
         }
 
-        if (ioctl(fd, VT_OPENQRY, &session_vt) < 0) {
-                g_debug ("GdmSessionWorker: couldn't open new VT: %m");
-                goto fail;
+        /* First adopt any pre-existing VT own by a session going down
+         */
+        session_vt = find_vt_of_closing_session (worker);
+
+        if (session_vt <= 0) {
+                if (ioctl(fd, VT_OPENQRY, &session_vt) < 0) {
+                        g_debug ("GdmSessionWorker: couldn't open new VT: %m");
+                        goto fail;
+                }
         }
 
         worker->priv->login_vt = vt_state.v_active;