printk.c

Kernel code of linux kernel

{
	struct console_cmdline *c;
	int i;

	for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
		if (strcmp(console_cmdline[i].name, name) == 0 &&
			  console_cmdline[i].index == idx) {
				c = &console_cmdline[i];
				strlcpy(c->name, name_new, sizeof(c->name));
				c->name[sizeof(c->name) - 1] = 0;
				c->options = options;
				c->index = idx_new;
				return i;
		}
	/* not found */
	return -1;
}

int console_suspend_enabled = 1;
EXPORT_SYMBOL(console_suspend_enabled);

static int __init console_suspend_disable(char *str)
{
	console_suspend_enabled = 0;
	return 1;
}
__setup("no_console_suspend", console_suspend_disable);

/**
 * suspend_console - suspend the console subsystem
 *
 * This disables printk() while we go into suspend states
 */
void suspend_console(void)
{
	if (!console_suspend_enabled)
		return;
	printk("Suspending console(s) (use no_console_suspend to debug)\n");
	acquire_console_sem();
	console_suspended = 1;
}

void resume_console(void)
{
	if (!console_suspend_enabled)
		return;
	console_suspended = 0;
	release_console_sem();
}

/**
 * acquire_console_sem - lock the console system for exclusive use.
 *
 * Acquires a semaphore which guarantees that the caller has
 * exclusive access to the console system and the console_drivers list.
 *
 * Can sleep, returns nothing.
 */
void acquire_console_sem(void)
{
	BUG_ON(in_interrupt());
	if (console_suspended) {
		down(&secondary_console_sem);
		return;
	}
	down(&console_sem);
	console_locked = 1;
	console_may_schedule = 1;
}
EXPORT_SYMBOL(acquire_console_sem);

int try_acquire_console_sem(void)
{
	if (down_trylock(&console_sem))
		return -1;
	console_locked = 1;
	console_may_schedule = 0;
	return 0;
}
EXPORT_SYMBOL(try_acquire_console_sem);

int is_console_locked(void)
{
	return console_locked;
}

void wake_up_klogd(void)
{
	if (!oops_in_progress && waitqueue_active(&log_wait))
		wake_up_interruptible(&log_wait);
}

/**
 * release_console_sem - unlock the console system
 *
 * Releases the semaphore which the caller holds on the console system
 * and the console driver list.
 *
 * While the semaphore was held, console output may have been buffered
 * by printk().  If this is the case, release_console_sem() emits
 * the output prior to releasing the semaphore.
 *
 * If there is output waiting for klogd, we wake it up.
 *
 * release_console_sem() may be called from any context.
 */
void release_console_sem(void)
{
	unsigned long flags;
	unsigned _con_start, _log_end;
	unsigned wake_klogd = 0;

	if (console_suspended) {
		up(&secondary_console_sem);
		return;
	}

	console_may_schedule = 0;

	for ( ; ; ) {
		spin_lock_irqsave(&logbuf_lock, flags);
		wake_klogd |= log_start - log_end;
		if (con_start == log_end)
			break;			/* Nothing to print */
		_con_start = con_start;
		_log_end = log_end;
		con_start = log_end;		/* Flush */
		spin_unlock(&logbuf_lock);
		stop_critical_timings();	/* don't trace print latency */
		call_console_drivers(_con_start, _log_end);
		start_critical_timings();
		local_irq_restore(flags);
	}
	console_locked = 0;
	up(&console_sem);
	spin_unlock_irqrestore(&logbuf_lock, flags);
	if (wake_klogd)
		wake_up_klogd();
}
EXPORT_SYMBOL(release_console_sem);

/**
 * console_conditional_schedule - yield the CPU if required
 *
 * If the console code is currently allowed to sleep, and
 * if this CPU should yield the CPU to another task, do
 * so here.
 *
 * Must be called within acquire_console_sem().
 */
void __sched console_conditional_schedule(void)
{
	if (console_may_schedule)
		cond_resched();
}
EXPORT_SYMBOL(console_conditional_schedule);

void console_print(const char *s)
{
	printk(KERN_EMERG "%s", s);
}
EXPORT_SYMBOL(console_print);

void console_unblank(void)
{
	struct console *c;

	/*
	 * console_unblank can no longer be called in interrupt context unless
	 * oops_in_progress is set to 1..
	 */
	if (oops_in_progress) {
		if (down_trylock(&console_sem) != 0)
			return;
	} else
		acquire_console_sem();

	console_locked = 1;
	console_may_schedule = 0;
	for (c = console_drivers; c != NULL; c = c->next)
		if ((c->flags & CON_ENABLED) && c->unblank)
			c->unblank();
	release_console_sem();
}

/*
 * Return the console tty driver structure and its associated index
 */
struct tty_driver *console_device(int *index)
{
	struct console *c;
	struct tty_driver *driver = NULL;

	acquire_console_sem();
	for (c = console_drivers; c != NULL; c = c->next) {
		if (!c->device)
			continue;
		driver = c->device(c, index);
		if (driver)
			break;
	}
	release_console_sem();
	return driver;
}

/*
 * Prevent further output on the passed console device so that (for example)
 * serial drivers can disable console output before suspending a port, and can
 * re-enable output afterwards.
 */
void console_stop(struct console *console)
{
	acquire_console_sem();
	console->flags &= ~CON_ENABLED;
	release_console_sem();
}
EXPORT_SYMBOL(console_stop);

void console_start(struct console *console)
{
	acquire_console_sem();
	console->flags |= CON_ENABLED;
	release_console_sem();
}
EXPORT_SYMBOL(console_start);

/*
 * The console driver calls this routine during kernel initialization
 * 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.
 */
void register_console(struct console *console)
{
	int i;
	unsigned long flags;
	struct console *bootconsole = NULL;

	if (console_drivers) {
		if (console->flags & CON_BOOT)
			return;
		if (console_drivers->flags & CON_BOOT)
			bootconsole = console_drivers;
	}

	if (preferred_console < 0 || bootconsole || !console_drivers)
		preferred_console = selected_console;

	if (console->early_setup)
		console->early_setup();

	/*
	 *	See if we want to use this console driver. If we
	 *	didn't select a console we take the first one
	 *	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;
				preferred_console = 0;
			}
		}
	}

	/*
	 *	See if this console matches one we selected on
	 *	the command line.
	 */
	for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
			i++) {
		if (strcmp(console_cmdline[i].name, console->name) != 0)
			continue;
		if (console->index >= 0 &&
		    console->index != console_cmdline[i].index)
			continue;
		if (console->index < 0)
			console->index = console_cmdline[i].index;
#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
		if (console_cmdline[i].brl_options) {
			console->flags |= CON_BRL;
			braille_register_console(console,
					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)
			break;
		console->flags |= CON_ENABLED;
		console->index = console_cmdline[i].index;
		if (i == selected_console) {
			console->flags |= CON_CONSDEV;
			preferred_console = selected_console;
		}
		break;
	}

	if (!(console->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;
	} else {
		printk(KERN_INFO "console [%s%d] enabled\n",
		       console->name, console->index);
	}

	/*
	 *	Put this console in the list - keep the
	 *	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;
	} else {
		console->next = console_drivers->next;
		console_drivers->next = console;
	}
	if (console->flags & CON_PRINTBUFFER) {
		/*
		 * release_console_sem() will print out the buffered messages
		 * for us.
		 */
		spin_lock_irqsave(&logbuf_lock, flags);
		con_start = log_start;
		spin_unlock_irqrestore(&logbuf_lock, flags);
	}
	release_console_sem();
}
EXPORT_SYMBOL(register_console);

int unregister_console(struct console *console)
{
        struct console *a, *b;
	int res = 1;

#ifdef CONFIG_A11Y_BRAILLE_CONSOLE
	if (console->flags & CON_BRL)
		return braille_unregister_console(console);
#endif

	acquire_console_sem();
	if (console_drivers == console) {
		console_drivers=console->next;
		res = 0;
	} else if (console_drivers) {
		for (a=console_drivers->next, b=console_drivers ;
		     a; b=a, a=b->next) {
			if (a == console) {
				b->next = a->next;
				res = 0;
				break;
			}
		}
	}

	/*
	 * If this isn't the last console and it has CON_CONSDEV set, we
	 * need to set it on the next preferred console.
	 */
	if (console_drivers != NULL && console->flags & CON_CONSDEV)
		console_drivers->flags |= CON_CONSDEV;

	release_console_sem();
	return res;
}
EXPORT_SYMBOL(unregister_console);

static int __init disable_boot_consoles(void)
{
	if (console_drivers != NULL) {
		if (console_drivers->flags & CON_BOOT) {
			printk(KERN_INFO "turn off boot console %s%d\n",
				console_drivers->name, console_drivers->index);
			return unregister_console(console_drivers);
		}
	}
	return 0;
}
late_initcall(disable_boot_consoles);

/**
 * tty_write_message - write a message to a certain tty, not just the console.
 * @tty: the destination tty_struct
 * @msg: the message to write
 *
 * This is used for messages that need to be redirected to a specific tty.
 * We don't put it into the syslog queue right now maybe in the future if
 * really needed.
 */
void tty_write_message(struct tty_struct *tty, char *msg)
{
	if (tty && tty->ops->write)
		tty->ops->write(tty, msg, strlen(msg));
	return;
}

#if defined CONFIG_PRINTK

/*
 * printk rate limiting, lifted from the networking subsystem.
 *
 * This enforces a rate limit: not more than 10 kernel messages
 * every 5s to make a denial-of-service attack impossible.
 */
DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);

int printk_ratelimit(void)
{
	return __ratelimit(&printk_ratelimit_state);
}
EXPORT_SYMBOL(printk_ratelimit);

/**
 * printk_timed_ratelimit - caller-controlled printk ratelimiting
 * @caller_jiffies: pointer to caller's state
 * @interval_msecs: minimum interval between prints
 *
 * printk_timed_ratelimit() returns true if more than @interval_msecs
 * milliseconds have elapsed since the last time printk_timed_ratelimit()
 * returned true.
 */
bool printk_timed_ratelimit(unsigned long *caller_jiffies,
			unsigned int interval_msecs)
{
	if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
		*caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
		return true;
	}
	return false;
}
EXPORT_SYMBOL(printk_timed_ratelimit);
#endif