Commit 4d091611 authored by Robin Getz's avatar Robin Getz Committed by Ingo Molnar
Browse files

printk: Enable the use of more than one CON_BOOT (early console) 



Today, register_console() assumes the following usage:

  - The first console to register with a flag set to CON_BOOT
    is the one and only bootconsole.

  - If another register_console() is called with an additional
    CON_BOOT, it is silently rejected.

  - As soon as a console without the CON_BOOT set calls
    registers the bootconsole is automatically unregistered.

  - Once there is a "real" console - register_console() will
    silently reject any consoles with it's CON_BOOT flag set.

In many systems (alpha, blackfin, microblaze, mips, powerpc,
sh, & x86), there are early_printk implementations, which use
the CON_BOOT which come out serial ports, vga, usb, & memory
buffers.

In many embedded systems, it would be nice to have two
bootconsoles - in case the primary fails, you always have
access to a backup memory buffer - but this requires at least
two CON_BOOT consoles...

This patch enables that functionality.

With the change applied, on boot you get (if you try to
re-enable a boot console after the "real" console has been
registered):

  root:/> dmesg | grep console
  bootconsole [early_shadow0] enabled
  bootconsole [early_BFuart0] enabled
  Kernel command line: root=/dev/mtdblock0 rw earlyprintk=serial,uart0,57600 console=ttyBF0,57600 nmi_debug=regs
  console handover:boot [early_BFuart0] boot [early_shadow0]  -> real [ttyBF0]
  Too late to register bootconsole early_shadow0

or:

  root:/> dmesg | grep console
  Kernel command line: root=/dev/mtdblock0 rw console=ttyBF0,57600
  console [ttyBF0] enabled

Signed-off-by: default avatarRobin Getz <rgetz@blackfin.uclinux.org>
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>
Cc: "Andrew Morton" <akpm@linux-foundation.org>
Cc: "Mike Frysinger" <vapier.adi@gmail.com>
Cc: "Paul Mundt" <lethal@linux-sh.org>
LKML-Reference: <200907012108.38030.rgetz@blackfin.uclinux.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 7c5371c4

kernel/printk.c

+92 −54
Original line number Diff line number Diff line
@@ -36,6 +36,12 @@ 


#include <asm/uaccess.h>



/*

 * for_each_console() allows you to iterate on each console

 */

#define for_each_console(con) \

	for (con = console_drivers; con != NULL; con = con->next)



/*

 * Architectures can override it:

 */
@@ -412,7 +418,7 @@ static void __call_console_drivers(unsigned start, unsigned end) 
{

	struct console *con;



	for (con = console_drivers; con; con = con->next) {

	for_each_console(con) {

		if ((con->flags & CON_ENABLED) && con->write &&

				(cpu_online(smp_processor_id()) ||

				(con->flags & CON_ANYTIME)))
@@ -544,7 +550,7 @@ static int have_callable_console(void) 
{

	struct console *con;



	for (con = console_drivers; con; con = con->next)

	for_each_console(con)

		if (con->flags & CON_ANYTIME)

			return 1;
@@ -1082,7 +1088,7 @@ void console_unblank(void) 


	console_locked = 1;

	console_may_schedule = 0;

	for (c = console_drivers; c != NULL; c = c->next)

	for_each_console(c)

		if ((c->flags & CON_ENABLED) && c->unblank)

			c->unblank();

	release_console_sem();
@@ -1097,7 +1103,7 @@ struct tty_driver *console_device(int *index) 
	struct tty_driver *driver = NULL;



	acquire_console_sem();

	for (c = console_drivers; c != NULL; c = c->next) {

	for_each_console(c) {

		if (!c->device)

			continue;

		driver = c->device(c, index);
@@ -1134,25 +1140,49 @@ EXPORT_SYMBOL(console_start); 
 * to register the console printing procedure with printk() and to

 * print any messages that were printed by the kernel before the

 * console driver was initialized.

 *

 * This can happen pretty early during the boot process (because of

 * early_printk) - sometimes before setup_arch() completes - be careful

 * of what kernel features are used - they may not be initialised yet.

 *

 * There are two types of consoles - bootconsoles (early_printk) and

 * "real" consoles (everything which is not a bootconsole) which are

 * handled differently.

 *  - Any number of bootconsoles can be registered at any time.

 *  - As soon as a "real" console is registered, all bootconsoles

 *    will be unregistered automatically.

 *  - Once a "real" console is registered, any attempt to register a

 *    bootconsoles will be rejected

 */

void register_console(struct console *console)

void register_console(struct console *newcon)

{

	int i;

	unsigned long flags;

	struct console *bootconsole = NULL;

	struct console *bcon = NULL;



	if (console_drivers) {

		if (console->flags & CON_BOOT)

	/*

	 * before we register a new CON_BOOT console, make sure we don't

	 * already have a valid console

	 */

	if (console_drivers && newcon->flags & CON_BOOT) {

		/* find the last or real console */

		for_each_console(bcon) {

			if (!(bcon->flags & CON_BOOT)) {

				printk(KERN_INFO "Too late to register bootconsole %s%d\n",

					newcon->name, newcon->index);

				return;

		if (console_drivers->flags & CON_BOOT)

			bootconsole = console_drivers;

			}

		}

	}



	if (console_drivers && console_drivers->flags & CON_BOOT)

		bcon = console_drivers;



	if (preferred_console < 0 || bootconsole || !console_drivers)

	if (preferred_console < 0 || bcon || !console_drivers)

		preferred_console = selected_console;



	if (console->early_setup)

		console->early_setup();

	if (newcon->early_setup)

		newcon->early_setup();



	/*

	 *	See if we want to use this console driver. If we
@@ -1160,13 +1190,13 @@ void register_console(struct console *console) 
	 *	that registers here.

	 */

	if (preferred_console < 0) {

		if (console->index < 0)

			console->index = 0;

		if (console->setup == NULL ||

		    console->setup(console, NULL) == 0) {

			console->flags |= CON_ENABLED;

			if (console->device) {

				console->flags |= CON_CONSDEV;

		if (newcon->index < 0)

			newcon->index = 0;

		if (newcon->setup == NULL ||

		    newcon->setup(newcon, NULL) == 0) {

			newcon->flags |= CON_ENABLED;

			if (newcon->device) {

				newcon->flags |= CON_CONSDEV;

				preferred_console = 0;

			}

		}
@@ -1178,47 +1208,53 @@ void register_console(struct console *console) 
	 */

	for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];

			i++) {

		if (strcmp(console_cmdline[i].name, console->name) != 0)

		if (strcmp(console_cmdline[i].name, newcon->name) != 0)

			continue;

		if (console->index >= 0 &&

		    console->index != console_cmdline[i].index)

		if (newcon->index >= 0 &&

		    newcon->index != console_cmdline[i].index)

			continue;

		if (console->index < 0)

			console->index = console_cmdline[i].index;

		if (newcon->index < 0)

			newcon->index = console_cmdline[i].index;

#ifdef CONFIG_A11Y_BRAILLE_CONSOLE

		if (console_cmdline[i].brl_options) {

			console->flags |= CON_BRL;

			braille_register_console(console,

			newcon->flags |= CON_BRL;

			braille_register_console(newcon,

					console_cmdline[i].index,

					console_cmdline[i].options,

					console_cmdline[i].brl_options);

			return;

		}

#endif

		if (console->setup &&

		    console->setup(console, console_cmdline[i].options) != 0)

		if (newcon->setup &&

		    newcon->setup(newcon, console_cmdline[i].options) != 0)

			break;

		console->flags |= CON_ENABLED;

		console->index = console_cmdline[i].index;

		newcon->flags |= CON_ENABLED;

		newcon->index = console_cmdline[i].index;

		if (i == selected_console) {

			console->flags |= CON_CONSDEV;

			newcon->flags |= CON_CONSDEV;

			preferred_console = selected_console;

		}

		break;

	}



	if (!(console->flags & CON_ENABLED))

	if (!(newcon->flags & CON_ENABLED))

		return;



	if (bootconsole && (console->flags & CON_CONSDEV)) {

		printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",

		       bootconsole->name, bootconsole->index,

		       console->name, console->index);

		unregister_console(bootconsole);

		console->flags &= ~CON_PRINTBUFFER;

	if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {

		/* we need to iterate through twice, to make sure we print

		 * everything out, before we unregister the console(s)

		 */

		printk(KERN_INFO "console handover:");

		for_each_console(bcon)

			printk("boot [%s%d] ", bcon->name, bcon->index);

		printk(" -> real [%s%d]\n", newcon->name, newcon->index);

		for_each_console(bcon)

			unregister_console(bcon);

		newcon->flags &= ~CON_PRINTBUFFER;

	} else {

		printk(KERN_INFO "console [%s%d] enabled\n",

		       console->name, console->index);

		printk(KERN_INFO "%sconsole [%s%d] enabled\n",

			(newcon->flags & CON_BOOT) ? "boot" : "" ,

			newcon->name, newcon->index);

	}



	/*
@@ -1226,16 +1262,16 @@ void register_console(struct console *console) 
	 *	preferred driver at the head of the list.

	 */

	acquire_console_sem();

	if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {

		console->next = console_drivers;

		console_drivers = console;

		if (console->next)

			console->next->flags &= ~CON_CONSDEV;

	if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {

		newcon->next = console_drivers;

		console_drivers = newcon;

		if (newcon->next)

			newcon->next->flags &= ~CON_CONSDEV;

	} else {

		console->next = console_drivers->next;

		console_drivers->next = console;

		newcon->next = console_drivers->next;

		console_drivers->next = newcon;

	}

	if (console->flags & CON_PRINTBUFFER) {

	if (newcon->flags & CON_PRINTBUFFER) {

		/*

		 * release_console_sem() will print out the buffered messages

		 * for us.
@@ -1287,11 +1323,13 @@ EXPORT_SYMBOL(unregister_console); 


static int __init disable_boot_consoles(void)

{

	if (console_drivers != NULL) {

		if (console_drivers->flags & CON_BOOT) {

	struct console *con;



	for_each_console(con) {

		if (con->flags & CON_BOOT) {

			printk(KERN_INFO "turn off boot console %s%d\n",

				console_drivers->name, console_drivers->index);

			return unregister_console(console_drivers);

				con->name, con->index);

			return unregister_console(con);

		}

	}

	return 0;

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