printk.c

Linux2.4.20针对三星公司的s3c2410开发板的内核改造。

		if (	msg_level < 0 &&
			((end - cur_index) > 2) &&
			LOG_BUF(cur_index + 0) == '<' &&
			LOG_BUF(cur_index + 1) >= '0' &&
			LOG_BUF(cur_index + 1) <= '7' &&
			LOG_BUF(cur_index + 2) == '>')
		{
			msg_level = LOG_BUF(cur_index + 1) - '0';
			cur_index += 3;
			start_print = cur_index;
		}
		while (cur_index != end) {
			char c = LOG_BUF(cur_index);
			cur_index++;

			if (c == '\n') {
				if (msg_level < 0) {
					/*
					 * printk() has already given us loglevel tags in
					 * the buffer.  This code is here in case the
					 * log buffer has wrapped right round and scribbled
					 * on those tags
					 */
					msg_level = default_message_loglevel;
				}
				_call_console_drivers(start_print, cur_index, msg_level);
				msg_level = -1;
				start_print = cur_index;
				break;
			}
		}
	}
	_call_console_drivers(start_print, end, msg_level);
}

static void emit_log_char(char c)
{
	LOG_BUF(log_end) = c;
	log_end++;
	if (log_end - log_start > LOG_BUF_LEN)
		log_start = log_end - LOG_BUF_LEN;
	if (log_end - con_start > LOG_BUF_LEN)
		con_start = log_end - LOG_BUF_LEN;
	if (logged_chars < LOG_BUF_LEN)
		logged_chars++;
}

/*
 * This is printk.  It can be called from any context.  We want it to work.
 * 
 * We try to grab the console_sem.  If we succeed, it's easy - we log the output and
 * call the console drivers.  If we fail to get the semaphore we place the output
 * into the log buffer and return.  The current holder of the console_sem will
 * notice the new output in release_console_sem() and will send it to the
 * consoles before releasing the semaphore.
 *
 * One effect of this deferred printing is that code which calls printk() and
 * then changes console_loglevel may break. This is because console_loglevel
 * is inspected when the actual printing occurs.
 */
asmlinkage int printk(const char *fmt, ...)
{
	va_list args;
	unsigned long flags;
	int printed_len;
	char *p;
	static char printk_buf[1024];
	static int log_level_unknown = 1;

	if (oops_in_progress) {
		/* If a crash is occurring, make sure we can't deadlock */
		spin_lock_init(&logbuf_lock);
		/* And make sure that we print immediately */
		init_MUTEX(&console_sem);
	}

	/* This stops the holder of console_sem just where we want him */
	spin_lock_irqsave(&logbuf_lock, flags);

	/* Emit the output into the temporary buffer */
	va_start(args, fmt);
	printed_len = vsnprintf(printk_buf, sizeof(printk_buf), fmt, args);
	va_end(args);

	/*
	 * Copy the output into log_buf.  If the caller didn't provide
	 * appropriate log level tags, we insert them here
	 */
#if	defined(CONFIG_DEBUG_LL)
	{
		extern void printascii(const char *);
		printascii(printk_buf);
	}
#endif
	for (p = printk_buf; *p; p++) {
		if (log_level_unknown) {
			if (p[0] != '<' || p[1] < '0' || p[1] > '7' || p[2] != '>') {
				emit_log_char('<');
				emit_log_char(default_message_loglevel + '0');
				emit_log_char('>');
			}
			log_level_unknown = 0;
		}
		emit_log_char(*p);
		if (*p == '\n')
			log_level_unknown = 1;
	}

	if (!arch_consoles_callable()) {
		/*
		 * On some architectures, the consoles are not usable
		 * on secondary CPUs early in the boot process.
		 */
		spin_unlock_irqrestore(&logbuf_lock, flags);
		goto out;
	}
	if (!down_trylock(&console_sem)) {
		/*
		 * We own the drivers.  We can drop the spinlock and let
		 * release_console_sem() print the text
		 */
		spin_unlock_irqrestore(&logbuf_lock, flags);
		console_may_schedule = 0;
		release_console_sem();
	} else {
		/*
		 * Someone else owns the drivers.  We drop the spinlock, which
		 * allows the semaphore holder to proceed and to call the
		 * console drivers with the output which we just produced.
		 */
		spin_unlock_irqrestore(&logbuf_lock, flags);
	}
out:
	return printed_len;
}
EXPORT_SYMBOL(printk);

/**
 * 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)
{
	if (in_interrupt())
		BUG();
	down(&console_sem);
	console_may_schedule = 1;
}
EXPORT_SYMBOL(acquire_console_sem);

/**
 * 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 long _con_start, _log_end;
	unsigned long must_wake_klogd = 0;

	for ( ; ; ) {
		spin_lock_irqsave(&logbuf_lock, flags);
		must_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_irqrestore(&logbuf_lock, flags);
		call_console_drivers(_con_start, _log_end);
	}
	console_may_schedule = 0;
	up(&console_sem);
	spin_unlock_irqrestore(&logbuf_lock, flags);
	if (must_wake_klogd && !oops_in_progress)
		wake_up_interruptible(&log_wait);
}

/** 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 console_conditional_schedule(void)
{
	if (console_may_schedule && current->need_resched) {
		set_current_state(TASK_RUNNING);
		schedule();
	}
}

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

void console_unblank(void)
{
	struct console *c;

	acquire_console_sem();
	for (c = console_drivers; c != NULL; c = c->next)
		if ((c->flags & CON_ENABLED) && c->unblank)
			c->unblank();
	release_console_sem();
}
EXPORT_SYMBOL(console_unblank);

/*
 * 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;

	/*
	 *	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 | 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;
		if (console->setup &&
		    console->setup(console, console_cmdline[i].options) != 0)
			break;
		console->flags |= CON_ENABLED;
		console->index = console_cmdline[i].index;
		if (i == preferred_console)
			console->flags |= CON_CONSDEV;
		break;
	}

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

	/*
	 *	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;
	} else {
		console->next = console_drivers->next;
		console_drivers->next = console;
	}
	if (console->flags & CON_PRINTBUFFER) {
		/*
		 * release_cosole_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;

	acquire_console_sem();
	if (console_drivers == console) {
		console_drivers=console->next;
		res = 0;
	} else {
		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 last console is removed, we re-enable picking the first
	 * one that gets registered. Without that, pmac early boot console
	 * would prevent fbcon from taking over.
	 */
	if (console_drivers == NULL)
		preferred_console = -1;
		

	release_console_sem();
	return res;
}
EXPORT_SYMBOL(unregister_console);
	
/**
 * tty_write_message - write a message to a certain tty, not just the console.
 *
 * 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->driver.write)
		tty->driver.write(tty, 0, msg, strlen(msg));
	return;
}