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vt: introduce and use vt_kmsg_redirect() function
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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 <[email protected]>
Cc: Alan Cox <[email protected]>
Cc: Ingo Molnar <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
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bwalle authored and torvalds committed Dec 15, 2009
1 parent c95d1e5 commit 5ada918
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Showing 4 changed files with 55 additions and 12 deletions.
43 changes: 37 additions & 6 deletions drivers/char/vt.c
Original file line number Diff line number Diff line change
Expand Up @@ -184,12 +184,10 @@ static DECLARE_WORK(console_work, console_callback);
* fg_console is the current virtual console,
* last_console is the last used one,
* want_console is the console we want to switch to,
* kmsg_redirect is the console for kernel messages,
*/
int fg_console;
int last_console;
int want_console = -1;
int kmsg_redirect;

/*
* For each existing display, we have a pointer to console currently visible
Expand Down Expand Up @@ -2434,6 +2432,37 @@ struct tty_driver *console_driver;

#ifdef CONFIG_VT_CONSOLE

/**
* vt_kmsg_redirect() - Sets/gets the kernel message console
* @new: The new virtual terminal number or -1 if the console should stay
* unchanged
*
* By default, the kernel messages are always printed on the current virtual
* console. However, the user may modify that default with the
* TIOCL_SETKMSGREDIRECT ioctl call.
*
* This function sets the kernel message console to be @new. It returns the old
* virtual console number. The virtual terminal number 0 (both as parameter and
* return value) means no redirection (i.e. always printed on the currently
* active console).
*
* The parameter -1 means that only the current console is returned, but the
* value is not modified. You may use the macro vt_get_kmsg_redirect() in that
* case to make the code more understandable.
*
* When the kernel is compiled without CONFIG_VT_CONSOLE, this function ignores
* the parameter and always returns 0.
*/
int vt_kmsg_redirect(int new)
{
static int kmsg_con;

if (new != -1)
return xchg(&kmsg_con, new);
else
return kmsg_con;
}

/*
* Console on virtual terminal
*
Expand All @@ -2448,15 +2477,17 @@ static void vt_console_print(struct console *co, const char *b, unsigned count)
const ushort *start;
ushort cnt = 0;
ushort myx;
int kmsg_console;

/* console busy or not yet initialized */
if (!printable)
return;
if (!spin_trylock(&printing_lock))
return;

if (kmsg_redirect && vc_cons_allocated(kmsg_redirect - 1))
vc = vc_cons[kmsg_redirect - 1].d;
kmsg_console = vt_get_kmsg_redirect();
if (kmsg_console && vc_cons_allocated(kmsg_console - 1))
vc = vc_cons[kmsg_console - 1].d;

/* read `x' only after setting currcons properly (otherwise
the `x' macro will read the x of the foreground console). */
Expand Down Expand Up @@ -2613,7 +2644,7 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
ret = set_vesa_blanking(p);
break;
case TIOCL_GETKMSGREDIRECT:
data = kmsg_redirect;
data = vt_get_kmsg_redirect();
ret = __put_user(data, p);
break;
case TIOCL_SETKMSGREDIRECT:
Expand All @@ -2623,7 +2654,7 @@ int tioclinux(struct tty_struct *tty, unsigned long arg)
if (get_user(data, p+1))
ret = -EFAULT;
else
kmsg_redirect = data;
vt_kmsg_redirect(data);
}
break;
case TIOCL_GETFGCONSOLE:
Expand Down
2 changes: 0 additions & 2 deletions include/linux/tty.h
Original file line number Diff line number Diff line change
Expand Up @@ -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);

Expand Down
15 changes: 15 additions & 0 deletions include/linux/vt.h
Original file line number Diff line number Diff line change
Expand Up @@ -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 */
7 changes: 3 additions & 4 deletions kernel/power/console.c
Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@

#include <linux/vt_kern.h>
#include <linux/kbd_kern.h>
#include <linux/console.h>
#include <linux/vt.h>
#include <linux/module.h>
#include "power.h"

Expand All @@ -21,16 +21,15 @@ int pm_prepare_console(void)
if (orig_fgconsole < 0)
return 1;

orig_kmsg = kmsg_redirect;
kmsg_redirect = SUSPEND_CONSOLE;
orig_kmsg = vt_kmsg_redirect(SUSPEND_CONSOLE);
return 0;
}

void pm_restore_console(void)
{
if (orig_fgconsole >= 0) {
vt_move_to_console(orig_fgconsole, 0);
kmsg_redirect = orig_kmsg;
vt_kmsg_redirect(orig_kmsg);
}
}
#endif

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