[gdm] worker: force KD_GRAPHICS mode before doing VT switch

[Ray Strode <halfline src gnome org>]

commit e699b438e64289c79f690e613399d935d9aac11c
Author: Ray Strode <rstrode redhat com>
Date:   Fri Feb 27 07:43:39 2015 -0500

    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

 daemon/gdm-session-worker.c |   50 +++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 48 insertions(+), 2 deletions(-)
---
diff --git a/daemon/gdm-session-worker.c b/daemon/gdm-session-worker.c
index a5c684c..470428b 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