hvc_console: Escape magic sysrq key

The ctrl-o (^O) is a common control key used by several applications,
such as vim, but hvc_console uses ^O as the magic-sysrq key.  This
commit allows users to send ^O to applications by pressing ^O twice
in succession.

To implement this, this commit introduces a check if ^O is pressed
again if the sysrq_pressed variable is already set.  In this case,
clear sysrq_pressed state and flip the ^O character to the tty.  (The
old behavior has always set "sysrq_pressed" if ^O has been entered,
and it has not flipped the ^O character to the tty.)

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index 74ecb5b2968..fb57f67bb42 100644
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -642,8 +642,11 @@ int hvc_poll(struct hvc_struct *hp)
                                 /* Handle the SysRq Hack */
                                 /* XXX should support a sequence */
                                 if (buf[i] == '\x0f') { /* ^O */
-                                        sysrq_pressed = 1;
-                                        continue;
+                                        /* if ^O is pressed again, reset
+                                         * sysrq_pressed and flip ^O char */
+                                        sysrq_pressed = !sysrq_pressed;
+                                        if (sysrq_pressed)
+                                                continue;
                                 } else if (sysrq_pressed) {
                                         handle_sysrq(buf[i], tty);
                                         sysrq_pressed = 0;