vt: introduce and use vt_kmsg_redirect() function

The kernel offers with TIOCL_GETKMSGREDIRECT ioctl() the possibility to
redirect the kernel messages to a specific console.

However, since it's not possible to switch to the kernel message console
after a panic(), it would be nice if the kernel would print the panic
message on the current console.

This patch series adds a new interface to access the global kmsg_redirect
variable by a function to be able to use it in code where
CONFIG_VT_CONSOLE is not set (kernel/panic.c).

This patch:

Instead of using and exporting a global value kmsg_redirect, introduce a
function vt_kmsg_redirect() that both can set and return the console where
messages are printed.

Change all users of kmsg_redirect (the VT code itself and kernel/power.c)
to the new interface.

The main advantage is that vt_kmsg_redirect() can also be used when
CONFIG_VT_CONSOLE is not set.

Signed-off-by: Bernhard Walle <bernhard@bwalle.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 15 insertions, 2 deletions

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 405a903..ef3a294 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -350,8 +350,6 @@ extern void tty_write_flush(struct tty_struct *);
 
 extern struct ktermios tty_std_termios;
 
-extern int kmsg_redirect;
-
 extern void console_init(void);
 extern int vcs_init(void);
 
diff --git a/include/linux/vt.h b/include/linux/vt.h
index 7ffa11f..3fb9944 100644
--- a/include/linux/vt.h
+++ b/include/linux/vt.h
@@ -84,4 +84,19 @@ struct vt_setactivate {
 
 #define VT_SETACTIVATE	0x560F	/* Activate and set the mode of a console */
 
+#ifdef CONFIG_VT_CONSOLE
+
+extern int vt_kmsg_redirect(int new);
+
+#else
+
+static inline int vt_kmsg_redirect(int new)
+{
+	return 0;
+}
+
+#endif
+
+#define vt_get_kmsg_redirect() vt_kmsg_redirect(-1)
+
 #endif /* _LINUX_VT_H */