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Subject[PATCH 34/36] tty: Add a new VT mode which is like VT_PROCESS but doesn't require a VT_RELDISP ioctl call
Date
From: Ari Entlich <atrigent@ccs.neu.edu>

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>
---
drivers/char/vt_ioctl.c | 39 ++++++++++++++++++++-------------------
include/linux/vt.h | 3 ++-
2 files changed, 22 insertions(+), 20 deletions(-)
diff --git a/drivers/char/vt_ioctl.c b/drivers/char/vt_ioctl.c
index 6aa1028..87778dc 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 d5dd0bc..778b7b2 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 */
--
1.7.0.1


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