worker: force KD_GRAPHICS mode before doing VT switch

If we switch VTs when in KD_TEXT mode there's obvious flicker.
This commit addresses that problem by going to KD_GRAPHICS mode
before switching VTs.  Ideally, we wouldn't switch VTs at all,
and instead leave it up to the display servers to manage via
logind. At the moment, the display servers don't use logind
properly, though, so do this as a stop gap.

https://bugzilla.gnome.org/show_bug.cgi?id=745031

1 files changed, 48 insertions, 2 deletions

diff --git a/daemon/gdm-session-worker.c b/daemon/gdm-session-worker.c
index a5c684c6..470428ba 100644
--- a/daemon/gdm-session-worker.c
+++ b/daemon/gdm-session-worker.c
@@ -31,6 +31,7 @@
 #ifdef WITH_SYSTEMD
 #include <sys/ioctl.h>
 #include <sys/vt.h>
+#include <sys/kd.h>
 #endif
 #include <errno.h>
 #include <grp.h>
@@ -105,6 +106,9 @@
 #define MAX_FILE_SIZE     65536
 #define MAX_LOGS          5
 
+#define RELEASE_DISPLAY_SIGNAL SIGUSR1
+#define ACQUIRE_DISPLAY_SIGNAL SIGUSR2
+
 enum {
         GDM_SESSION_WORKER_STATE_NONE = 0,
         GDM_SESSION_WORKER_STATE_SETUP_COMPLETE,
@@ -959,12 +963,51 @@ gdm_session_worker_stop_auditor (GdmSessionWorker *worker)
 
 #ifdef WITH_SYSTEMD
 static void
+on_release_display (int signal)
+{
+        int fd;
+
+        fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
+        ioctl(fd, VT_RELDISP, 1);
+        close(fd);
+}
+
+static void
+on_acquire_display (int signal)
+{
+        int fd;
+
+        fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
+        ioctl(fd, VT_RELDISP, VT_ACKACQ);
+        close(fd);
+}
+
+static void
 jump_to_vt (GdmSessionWorker  *worker,
             int                vt_number)
 {
         int fd;
+        gboolean just_opened_tty = FALSE;
+
+        if (worker->priv->session_tty_fd != -1) {
+                struct vt_mode setmode_request = { 0 };
+
+                fd = worker->priv->session_tty_fd;
+
+                ioctl (fd, KDSETMODE, KD_GRAPHICS);
+
+                setmode_request.mode = VT_PROCESS;
+                setmode_request.relsig = RELEASE_DISPLAY_SIGNAL;
+                setmode_request.acqsig = ACQUIRE_DISPLAY_SIGNAL;
+                ioctl (fd, VT_SETMODE, &setmode_request);
+
+                signal (RELEASE_DISPLAY_SIGNAL, on_release_display);
+                signal (ACQUIRE_DISPLAY_SIGNAL, on_acquire_display);
+        } else {
+                fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
+                just_opened_tty = TRUE;
+        }
 
-        fd = open ("/dev/tty0", O_RDWR | O_NOCTTY);
         if (ioctl (fd, VT_ACTIVATE, vt_number) < 0) {
                 g_debug ("GdmSessionWorker: couldn't initiate jump to VT %d: %m",
                          vt_number);
@@ -972,7 +1015,10 @@ jump_to_vt (GdmSessionWorker  *worker,
                 g_debug ("GdmSessionWorker: couldn't finalize jump to VT %d: %m",
                          vt_number);
         }
-        close(fd);
+
+        if (just_opened_tty) {
+                close(fd);
+        }
 }
 #endif