tty: Add a new VT mode which is like VT_PROCESS but doesn't require a VT_RELDISP ioctl call

This new VT mode (VT_PROCESS_AUTO) does everything that VT_PROCESS does
except that it doesn't wait for a VT_RELDISP ioctl before switching
away from a VT with that mode.

If the X server eventually uses this new mode, debugging and crash
recovery should become easier. This is because even when currently in
the VT of a frozen X server it would still be possible to switch out
by doing SysRq-r and then CTRL-<number of a text vt>, sshing in and
doing chvt <number of a text vt>, or any other method of VT switching.
The general concensus on #xorg-devel seems to be that it should be
safe to use this with X now that we have KMS.

This also moves the VT_ACKACQ define to a more appropriate place,
for clarity's sake.

Signed-off-by: Ari Entlich <atrigent@ccs.neu.edu>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 22 insertions, 20 deletions

diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 6aa10284104a..87778dcf8727 100644
--- a/drivers/char/vt_ioctl.c
+++ b/drivers/char/vt_ioctl.c
@@ -888,7 +888,7 @@ int vt_ioctl(struct tty_struct *tty, struct file * file,
                         ret = -EFAULT;
                         goto out;
                 }
-                if (tmp.mode != VT_AUTO && tmp.mode != VT_PROCESS) {
+                if (tmp.mode != VT_AUTO && tmp.mode != VT_PROCESS && tmp.mode != VT_PROCESS_AUTO) {
                         ret = -EINVAL;
                         goto out;
                 }
@@ -1622,7 +1622,7 @@ static void complete_change_console(struct vc_data *vc)
          * telling it that it has acquired. Also check if it has died and
          * clean up (similar to logic employed in change_console())
          */
-        if (vc->vt_mode.mode == VT_PROCESS) {
+        if (vc->vt_mode.mode == VT_PROCESS || vc->vt_mode.mode == VT_PROCESS_AUTO) {
                 /*
                  * Send the signal as privileged - kill_pid() will
                  * tell us if the process has gone or something else
@@ -1682,7 +1682,7 @@ void change_console(struct vc_data *new_vc)
          * vt to auto control.
          */
         vc = vc_cons[fg_console].d;
-        if (vc->vt_mode.mode == VT_PROCESS) {
+        if (vc->vt_mode.mode == VT_PROCESS || vc->vt_mode.mode == VT_PROCESS_AUTO) {
                 /*
                  * Send the signal as privileged - kill_pid() will
                  * tell us if the process has gone or something else
@@ -1693,27 +1693,28 @@ void change_console(struct vc_data *new_vc)
                  */
                 vc->vt_newvt = new_vc->vc_num;
                 if (kill_pid(vc->vt_pid, vc->vt_mode.relsig, 1) == 0) {
+                        if(vc->vt_mode.mode == VT_PROCESS)
+                                /*
+                                 * It worked. Mark the vt to switch to and
+                                 * return. The process needs to send us a
+                                 * VT_RELDISP ioctl to complete the switch.
+                                 */
+                                return;
+                } else {
                         /*
-                         * It worked. Mark the vt to switch to and
-                         * return. The process needs to send us a
-                         * VT_RELDISP ioctl to complete the switch.
+                         * The controlling process has died, so we revert back to
+                         * normal operation. In this case, we'll also change back
+                         * to KD_TEXT mode. I'm not sure if this is strictly correct
+                         * but it saves the agony when the X server dies and the screen
+                         * remains blanked due to KD_GRAPHICS! It would be nice to do
+                         * this outside of VT_PROCESS but there is no single process
+                         * to account for and tracking tty count may be undesirable.
                          */
-                        return;
+                        reset_vc(vc);
                 }
 
                 /*
-                 * The controlling process has died, so we revert back to
-                 * normal operation. In this case, we'll also change back
-                 * to KD_TEXT mode. I'm not sure if this is strictly correct
-                 * but it saves the agony when the X server dies and the screen
-                 * remains blanked due to KD_GRAPHICS! It would be nice to do
-                 * this outside of VT_PROCESS but there is no single process
-                 * to account for and tracking tty count may be undesirable.
-                 */
-                reset_vc(vc);
-
-                /*
-                 * Fall through to normal (VT_AUTO) handling of the switch...
+                 * Fall through to normal (VT_AUTO and VT_PROCESS_AUTO) handling of the switch...
                  */
         }
 
diff --git a/include/linux/vt.h b/include/linux/vt.h
index d5dd0bc408fd..778b7b2a47d4 100644
--- a/include/linux/vt.h
+++ b/include/linux/vt.h
@@ -27,7 +27,7 @@ struct vt_mode {
 #define VT_SETMODE      0x5602  /* set mode of active vt */
 #define         VT_AUTO         0x00    /* auto vt switching */
 #define         VT_PROCESS      0x01    /* process controls switching */
-#define         VT_ACKACQ       0x02    /* acknowledge switch */
+#define         VT_PROCESS_AUTO 0x02    /* process is notified of switching */
 
 struct vt_stat {
         unsigned short v_active;        /* active vt */
@@ -38,6 +38,7 @@ struct vt_stat {
 #define VT_SENDSIG      0x5604  /* signal to send to bitmask of vts */
 
 #define VT_RELDISP      0x5605  /* release display */
+#define         VT_ACKACQ       0x02    /* acknowledge switch */
 
 #define VT_ACTIVATE     0x5606  /* make vt active */
 #define VT_WAITACTIVE   0x5607  /* wait for vt active */