/*
   *  linux/kernel/printk.c
   *
   *  Copyright (C) 1991, 1992  Linus Torvalds
   *
   * Modified to make sys_syslog() more flexible: added commands to
   * return the last 4k of kernel messages, regardless of whether
   * they've been read or not.  Added option to suppress kernel printk's
   * to the console.  Added hook for sending the console messages
   * elsewhere, in preparation for a serial line console (someday).
   * Ted Ts'o, 2/11/93.
   * Modified for sysctl support, 1/8/97, Chris Horn.

   * Fixed SMP synchronization, 08/08/99, Manfred Spraul

   *     manfred@colorfullife.com

   * Rewrote bits to get rid of console_lock
   *	01Mar01 Andrew Morton <andrewm@uow.edu.au>
   */
  
  #include <linux/kernel.h>
  #include <linux/mm.h>
  #include <linux/tty.h>
  #include <linux/tty_driver.h>

  #include <linux/console.h>
  #include <linux/init.h>

  #include <linux/jiffies.h>
  #include <linux/nmi.h>

  #include <linux/module.h>

  #include <linux/moduleparam.h>

  #include <linux/interrupt.h>			/* For in_interrupt() */

  #include <linux/delay.h>
  #include <linux/smp.h>
  #include <linux/security.h>
  #include <linux/bootmem.h>
  #include <linux/syscalls.h>
  
  #include <asm/uaccess.h>

  /*
   * Architectures can override it:
   */
  void __attribute__((weak)) early_printk(const char *fmt, ...)
  {
  }

  #define __LOG_BUF_LEN	(1 << CONFIG_LOG_BUF_SHIFT)
  
  /* printk's without a loglevel use this.. */
  #define DEFAULT_MESSAGE_LOGLEVEL 4 /* KERN_WARNING */
  
  /* We show everything that is MORE important than this.. */
  #define MINIMUM_CONSOLE_LOGLEVEL 1 /* Minimum loglevel we let people use */
  #define DEFAULT_CONSOLE_LOGLEVEL 7 /* anything MORE serious than KERN_DEBUG */
  
  DECLARE_WAIT_QUEUE_HEAD(log_wait);
  
  int console_printk[4] = {
  	DEFAULT_CONSOLE_LOGLEVEL,	/* console_loglevel */
  	DEFAULT_MESSAGE_LOGLEVEL,	/* default_message_loglevel */
  	MINIMUM_CONSOLE_LOGLEVEL,	/* minimum_console_loglevel */
  	DEFAULT_CONSOLE_LOGLEVEL,	/* default_console_loglevel */
  };

  /*

   * Low level drivers may need that to know if they can schedule in

   * their unblank() callback or not. So let's export it.
   */
  int oops_in_progress;
  EXPORT_SYMBOL(oops_in_progress);
  
  /*
   * console_sem protects the console_drivers list, and also
   * provides serialisation for access to the entire console
   * driver system.
   */
  static DECLARE_MUTEX(console_sem);

  static DECLARE_MUTEX(secondary_console_sem);

  struct console *console_drivers;
  /*
   * This is used for debugging the mess that is the VT code by
   * keeping track if we have the console semaphore held. It's
   * definitely not the perfect debug tool (we don't know if _WE_
   * hold it are racing, but it helps tracking those weird code
   * path in the console code where we end up in places I want
   * locked without the console sempahore held
   */

  static int console_locked, console_suspended;

  
  /*
   * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
   * It is also used in interesting ways to provide interlocking in
   * release_console_sem().
   */
  static DEFINE_SPINLOCK(logbuf_lock);

  #define LOG_BUF_MASK (log_buf_len-1)

  #define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
  
  /*
   * The indices into log_buf are not constrained to log_buf_len - they
   * must be masked before subscripting
   */

  static unsigned log_start;	/* Index into log_buf: next char to be read by syslog() */
  static unsigned con_start;	/* Index into log_buf: next char to be sent to consoles */
  static unsigned log_end;	/* Index into log_buf: most-recently-written-char + 1 */

  
  /*
   *	Array of consoles built from command line options (console=)
   */
  struct console_cmdline
  {
  	char	name[8];			/* Name of the driver	    */
  	int	index;				/* Minor dev. to use	    */
  	char	*options;			/* Options for the driver   */

  #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
  	char	*brl_options;			/* Options for braille driver */
  #endif

  };
  
  #define MAX_CMDLINECONSOLES 8
  
  static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
  static int selected_console = -1;
  static int preferred_console = -1;
  
  /* Flag: console code may call schedule() */
  static int console_may_schedule;

  #ifdef CONFIG_PRINTK
  
  static char __log_buf[__LOG_BUF_LEN];
  static char *log_buf = __log_buf;
  static int log_buf_len = __LOG_BUF_LEN;

  static unsigned logged_chars; /* Number of chars produced since last read+clear operation */

  static int __init log_buf_len_setup(char *str)
  {

  	unsigned size = memparse(str, &str);

  	unsigned long flags;
  
  	if (size)
  		size = roundup_pow_of_two(size);
  	if (size > log_buf_len) {

  		unsigned start, dest_idx, offset;

  		char *new_log_buf;

  
  		new_log_buf = alloc_bootmem(size);
  		if (!new_log_buf) {

  			printk(KERN_WARNING "log_buf_len: allocation failed
  ");

  			goto out;
  		}
  
  		spin_lock_irqsave(&logbuf_lock, flags);
  		log_buf_len = size;
  		log_buf = new_log_buf;
  
  		offset = start = min(con_start, log_start);
  		dest_idx = 0;
  		while (start != log_end) {
  			log_buf[dest_idx] = __log_buf[start & (__LOG_BUF_LEN - 1)];
  			start++;
  			dest_idx++;
  		}
  		log_start -= offset;
  		con_start -= offset;
  		log_end -= offset;
  		spin_unlock_irqrestore(&logbuf_lock, flags);

  		printk(KERN_NOTICE "log_buf_len: %d
  ", log_buf_len);

  	}
  out:

  	return 1;
  }
  
  __setup("log_buf_len=", log_buf_len_setup);

  #ifdef CONFIG_BOOT_PRINTK_DELAY
  
  static unsigned int boot_delay; /* msecs delay after each printk during bootup */
  static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
  
  static int __init boot_delay_setup(char *str)
  {
  	unsigned long lpj;
  	unsigned long long loops_per_msec;
  
  	lpj = preset_lpj ? preset_lpj : 1000000;	/* some guess */
  	loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
  
  	get_option(&str, &boot_delay);
  	if (boot_delay > 10 * 1000)
  		boot_delay = 0;
  
  	printk_delay_msec = loops_per_msec;
  	printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
  		"HZ: %d, printk_delay_msec: %llu
  ",
  		boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
  	return 1;
  }
  __setup("boot_delay=", boot_delay_setup);
  
  static void boot_delay_msec(void)
  {
  	unsigned long long k;
  	unsigned long timeout;
  
  	if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
  		return;
  
  	k = (unsigned long long)printk_delay_msec * boot_delay;
  
  	timeout = jiffies + msecs_to_jiffies(boot_delay);
  	while (k) {
  		k--;
  		cpu_relax();
  		/*
  		 * use (volatile) jiffies to prevent
  		 * compiler reduction; loop termination via jiffies
  		 * is secondary and may or may not happen.
  		 */
  		if (time_after(jiffies, timeout))
  			break;
  		touch_nmi_watchdog();
  	}
  }
  #else
  static inline void boot_delay_msec(void)
  {
  }
  #endif

  /*

   * Return the number of unread characters in the log buffer.
   */
  int log_buf_get_len(void)
  {
  	return logged_chars;
  }
  
  /*
   * Copy a range of characters from the log buffer.
   */
  int log_buf_copy(char *dest, int idx, int len)
  {
  	int ret, max;
  	bool took_lock = false;
  
  	if (!oops_in_progress) {
  		spin_lock_irq(&logbuf_lock);
  		took_lock = true;
  	}
  
  	max = log_buf_get_len();
  	if (idx < 0 || idx >= max) {
  		ret = -1;
  	} else {
  		if (len > max)
  			len = max;
  		ret = len;
  		idx += (log_end - max);
  		while (len-- > 0)
  			dest[len] = LOG_BUF(idx + len);
  	}
  
  	if (took_lock)
  		spin_unlock_irq(&logbuf_lock);
  
  	return ret;
  }
  
  /*
   * Extract a single character from the log buffer.
   */
  int log_buf_read(int idx)
  {
  	char ret;
  
  	if (log_buf_copy(&ret, idx, 1) == 1)
  		return ret;
  	else
  		return -1;
  }
  
  /*

   * Commands to do_syslog:
   *
   * 	0 -- Close the log.  Currently a NOP.
   * 	1 -- Open the log. Currently a NOP.
   * 	2 -- Read from the log.
   * 	3 -- Read all messages remaining in the ring buffer.
   * 	4 -- Read and clear all messages remaining in the ring buffer
   * 	5 -- Clear ring buffer.
   * 	6 -- Disable printk's to console
   * 	7 -- Enable printk's to console
   *	8 -- Set level of messages printed to console
   *	9 -- Return number of unread characters in the log buffer
   *     10 -- Return size of the log buffer
   */

  int do_syslog(int type, char __user *buf, int len)

  {

  	unsigned i, j, limit, count;

  	int do_clear = 0;
  	char c;
  	int error = 0;
  
  	error = security_syslog(type);
  	if (error)
  		return error;
  
  	switch (type) {
  	case 0:		/* Close log */
  		break;
  	case 1:		/* Open log */
  		break;
  	case 2:		/* Read from log */
  		error = -EINVAL;
  		if (!buf || len < 0)
  			goto out;
  		error = 0;
  		if (!len)
  			goto out;
  		if (!access_ok(VERIFY_WRITE, buf, len)) {
  			error = -EFAULT;
  			goto out;
  		}

  		error = wait_event_interruptible(log_wait,
  							(log_start - log_end));

  		if (error)
  			goto out;
  		i = 0;
  		spin_lock_irq(&logbuf_lock);
  		while (!error && (log_start != log_end) && i < len) {
  			c = LOG_BUF(log_start);
  			log_start++;
  			spin_unlock_irq(&logbuf_lock);
  			error = __put_user(c,buf);
  			buf++;
  			i++;
  			cond_resched();
  			spin_lock_irq(&logbuf_lock);
  		}
  		spin_unlock_irq(&logbuf_lock);
  		if (!error)
  			error = i;
  		break;
  	case 4:		/* Read/clear last kernel messages */

  		do_clear = 1;

  		/* FALL THRU */
  	case 3:		/* Read last kernel messages */
  		error = -EINVAL;
  		if (!buf || len < 0)
  			goto out;
  		error = 0;
  		if (!len)
  			goto out;
  		if (!access_ok(VERIFY_WRITE, buf, len)) {
  			error = -EFAULT;
  			goto out;
  		}
  		count = len;
  		if (count > log_buf_len)
  			count = log_buf_len;
  		spin_lock_irq(&logbuf_lock);
  		if (count > logged_chars)
  			count = logged_chars;
  		if (do_clear)
  			logged_chars = 0;
  		limit = log_end;
  		/*
  		 * __put_user() could sleep, and while we sleep

  		 * printk() could overwrite the messages

  		 * we try to copy to user space. Therefore
  		 * the messages are copied in reverse. <manfreds>
  		 */

  		for (i = 0; i < count && !error; i++) {

  			j = limit-1-i;
  			if (j + log_buf_len < log_end)
  				break;
  			c = LOG_BUF(j);
  			spin_unlock_irq(&logbuf_lock);
  			error = __put_user(c,&buf[count-1-i]);
  			cond_resched();
  			spin_lock_irq(&logbuf_lock);
  		}
  		spin_unlock_irq(&logbuf_lock);
  		if (error)
  			break;
  		error = i;

  		if (i != count) {

  			int offset = count-error;
  			/* buffer overflow during copy, correct user buffer. */

  			for (i = 0; i < error; i++) {

  				if (__get_user(c,&buf[i+offset]) ||
  				    __put_user(c,&buf[i])) {
  					error = -EFAULT;
  					break;
  				}
  				cond_resched();
  			}
  		}
  		break;
  	case 5:		/* Clear ring buffer */
  		logged_chars = 0;
  		break;
  	case 6:		/* Disable logging to console */
  		console_loglevel = minimum_console_loglevel;
  		break;
  	case 7:		/* Enable logging to console */
  		console_loglevel = default_console_loglevel;
  		break;
  	case 8:		/* Set level of messages printed to console */
  		error = -EINVAL;
  		if (len < 1 || len > 8)
  			goto out;
  		if (len < minimum_console_loglevel)
  			len = minimum_console_loglevel;
  		console_loglevel = len;
  		error = 0;
  		break;
  	case 9:		/* Number of chars in the log buffer */
  		error = log_end - log_start;
  		break;
  	case 10:	/* Size of the log buffer */
  		error = log_buf_len;
  		break;
  	default:
  		error = -EINVAL;
  		break;
  	}
  out:
  	return error;
  }

  asmlinkage long sys_syslog(int type, char __user *buf, int len)

  {
  	return do_syslog(type, buf, len);
  }
  
  /*
   * Call the console drivers on a range of log_buf
   */

  static void __call_console_drivers(unsigned start, unsigned end)

  {
  	struct console *con;
  
  	for (con = console_drivers; con; con = con->next) {

  		if ((con->flags & CON_ENABLED) && con->write &&
  				(cpu_online(smp_processor_id()) ||
  				(con->flags & CON_ANYTIME)))

  			con->write(con, &LOG_BUF(start), end - start);
  	}
  }

  static int __read_mostly ignore_loglevel;

  static int __init ignore_loglevel_setup(char *str)

  {
  	ignore_loglevel = 1;
  	printk(KERN_INFO "debug: ignoring loglevel setting.
  ");

  	return 0;

  }

  early_param("ignore_loglevel", ignore_loglevel_setup);

  /*
   * Write out chars from start to end - 1 inclusive
   */

  static void _call_console_drivers(unsigned start,
  				unsigned end, int msg_log_level)

  {

  	if ((msg_log_level < console_loglevel || ignore_loglevel) &&

  			console_drivers && start != end) {
  		if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
  			/* wrapped write */
  			__call_console_drivers(start & LOG_BUF_MASK,
  						log_buf_len);
  			__call_console_drivers(0, end & LOG_BUF_MASK);
  		} else {
  			__call_console_drivers(start, end);
  		}
  	}
  }
  
  /*
   * Call the console drivers, asking them to write out
   * log_buf[start] to log_buf[end - 1].
   * The console_sem must be held.
   */

  static void call_console_drivers(unsigned start, unsigned end)

  {

  	unsigned cur_index, start_print;

  	static int msg_level = -1;

  	BUG_ON(((int)(start - end)) > 0);

  
  	cur_index = start;
  	start_print = start;
  	while (cur_index != end) {

  		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 == '
  ') {
  				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++;
  }
  
  /*
   * Zap console related locks when oopsing. Only zap at most once
   * every 10 seconds, to leave time for slow consoles to print a
   * full oops.
   */
  static void zap_locks(void)
  {
  	static unsigned long oops_timestamp;
  
  	if (time_after_eq(jiffies, oops_timestamp) &&

  			!time_after(jiffies, oops_timestamp + 30 * HZ))

  		return;
  
  	oops_timestamp = jiffies;
  
  	/* 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);
  }
  
  #if defined(CONFIG_PRINTK_TIME)
  static int printk_time = 1;
  #else
  static int printk_time = 0;
  #endif

  module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);

  /* Check if we have any console registered that can be called early in boot. */
  static int have_callable_console(void)
  {
  	struct console *con;
  
  	for (con = console_drivers; con; con = con->next)
  		if (con->flags & CON_ANYTIME)
  			return 1;
  
  	return 0;
  }

  /**
   * printk - print a kernel message
   * @fmt: format string
   *

   * This is printk().  It can be called from any context.  We want it to work.

   * Be aware of the fact that if oops_in_progress is not set, we might try to
   * wake klogd up which could deadlock on runqueue lock if printk() is called
   * from scheduler code.

   *

   * 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.

   *
   * See also:
   * printf(3)

   */

  asmlinkage int printk(const char *fmt, ...)
  {
  	va_list args;
  	int r;
  
  	va_start(args, fmt);
  	r = vprintk(fmt, args);
  	va_end(args);
  
  	return r;
  }

  /* cpu currently holding logbuf_lock */
  static volatile unsigned int printk_cpu = UINT_MAX;

  /*
   * Can we actually use the console at this time on this cpu?
   *
   * Console drivers may assume that per-cpu resources have
   * been allocated. So unless they're explicitly marked as
   * being able to cope (CON_ANYTIME) don't call them until
   * this CPU is officially up.
   */
  static inline int can_use_console(unsigned int cpu)
  {
  	return cpu_online(cpu) || have_callable_console();
  }
  
  /*
   * Try to get console ownership to actually show the kernel
   * messages from a 'printk'. Return true (and with the
   * console_semaphore held, and 'console_locked' set) if it
   * is successful, false otherwise.
   *
   * This gets called with the 'logbuf_lock' spinlock held and
   * interrupts disabled. It should return with 'lockbuf_lock'
   * released but interrupts still disabled.
   */
  static int acquire_console_semaphore_for_printk(unsigned int cpu)
  {
  	int retval = 0;

  	if (!try_acquire_console_sem()) {
  		retval = 1;
  
  		/*
  		 * If we can't use the console, we need to release
  		 * the console semaphore by hand to avoid flushing
  		 * the buffer. We need to hold the console semaphore
  		 * in order to do this test safely.
  		 */
  		if (!can_use_console(cpu)) {
  			console_locked = 0;
  			up(&console_sem);
  			retval = 0;
  		}
  	}

  	printk_cpu = UINT_MAX;
  	spin_unlock(&logbuf_lock);
  	return retval;
  }

  const char printk_recursion_bug_msg [] =
  			KERN_CRIT "BUG: recent printk recursion!
  ";
  static int printk_recursion_bug;

  asmlinkage int vprintk(const char *fmt, va_list args)
  {

  	static int log_level_unknown = 1;
  	static char printk_buf[1024];

  	unsigned long flags;

  	int printed_len = 0;
  	int this_cpu;

  	char *p;

  	boot_delay_msec();

  	preempt_disable();

  	/* This stops the holder of console_sem just where we want him */

  	raw_local_irq_save(flags);

  	this_cpu = smp_processor_id();
  
  	/*
  	 * Ouch, printk recursed into itself!
  	 */
  	if (unlikely(printk_cpu == this_cpu)) {
  		/*
  		 * If a crash is occurring during printk() on this CPU,
  		 * then try to get the crash message out but make sure
  		 * we can't deadlock. Otherwise just return to avoid the
  		 * recursion and return - but flag the recursion so that
  		 * it can be printed at the next appropriate moment:
  		 */
  		if (!oops_in_progress) {
  			printk_recursion_bug = 1;
  			goto out_restore_irqs;
  		}
  		zap_locks();
  	}

  	lockdep_off();
  	spin_lock(&logbuf_lock);

  	printk_cpu = this_cpu;

  	if (printk_recursion_bug) {
  		printk_recursion_bug = 0;
  		strcpy(printk_buf, printk_recursion_bug_msg);
  		printed_len = sizeof(printk_recursion_bug_msg);
  	}

  	/* Emit the output into the temporary buffer */

  	printed_len += vscnprintf(printk_buf + printed_len,

  				  sizeof(printk_buf) - printed_len, fmt, args);

  
  	/*
  	 * Copy the output into log_buf.  If the caller didn't provide
  	 * appropriate log level tags, we insert them here
  	 */
  	for (p = printk_buf; *p; p++) {
  		if (log_level_unknown) {
                          /* log_level_unknown signals the start of a new line */
  			if (printk_time) {
  				int loglev_char;
  				char tbuf[50], *tp;
  				unsigned tlen;
  				unsigned long long t;
  				unsigned long nanosec_rem;
  
  				/*
  				 * force the log level token to be
  				 * before the time output.
  				 */
  				if (p[0] == '<' && p[1] >='0' &&
  				   p[1] <= '7' && p[2] == '>') {
  					loglev_char = p[1];
  					p += 3;

  					printed_len -= 3;

  				} else {
  					loglev_char = default_message_loglevel
  						+ '0';
  				}

  				t = cpu_clock(printk_cpu);

  				nanosec_rem = do_div(t, 1000000000);
  				tlen = sprintf(tbuf,
  						"<%c>[%5lu.%06lu] ",
  						loglev_char,
  						(unsigned long)t,
  						nanosec_rem/1000);
  
  				for (tp = tbuf; tp < tbuf + tlen; tp++)
  					emit_log_char(*tp);

  				printed_len += tlen;

  			} else {
  				if (p[0] != '<' || p[1] < '0' ||
  				   p[1] > '7' || p[2] != '>') {
  					emit_log_char('<');
  					emit_log_char(default_message_loglevel
  						+ '0');
  					emit_log_char('>');

  					printed_len += 3;

  				}

  			}
  			log_level_unknown = 0;
  			if (!*p)
  				break;
  		}
  		emit_log_char(*p);
  		if (*p == '
  ')
  			log_level_unknown = 1;
  	}

  	/*
  	 * Try to acquire and then immediately release the
  	 * console semaphore. The release will do all the
  	 * actual magic (print out buffers, wake up klogd,
  	 * etc). 
  	 *
  	 * The acquire_console_semaphore_for_printk() function
  	 * will release 'logbuf_lock' regardless of whether it
  	 * actually gets the semaphore or not.
  	 */
  	if (acquire_console_semaphore_for_printk(this_cpu))
  		release_console_sem();

  	lockdep_on();

  out_restore_irqs:

  	raw_local_irq_restore(flags);

  	preempt_enable();

  	return printed_len;
  }
  EXPORT_SYMBOL(printk);
  EXPORT_SYMBOL(vprintk);

  #else

  asmlinkage long sys_syslog(int type, char __user *buf, int len)

  {

  	return -ENOSYS;

  }

  static void call_console_drivers(unsigned start, unsigned end)

  {
  }

  
  #endif

  static int __add_preferred_console(char *name, int idx, char *options,
  				   char *brl_options)
  {
  	struct console_cmdline *c;
  	int i;
  
  	/*
  	 *	See if this tty is not yet registered, and
  	 *	if we have a slot free.
  	 */
  	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) {
  				if (!brl_options)
  					selected_console = i;
  				return 0;
  		}
  	if (i == MAX_CMDLINECONSOLES)
  		return -E2BIG;
  	if (!brl_options)
  		selected_console = i;
  	c = &console_cmdline[i];
  	strlcpy(c->name, name, sizeof(c->name));
  	c->options = options;
  #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
  	c->brl_options = brl_options;
  #endif
  	c->index = idx;
  	return 0;
  }

  /*
   * Set up a list of consoles.  Called from init/main.c
   */
  static int __init console_setup(char *str)
  {

  	char buf[sizeof(console_cmdline[0].name) + 4]; /* 4 for index */

  	char *s, *options, *brl_options = NULL;

  	int idx;

  #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
  	if (!memcmp(str, "brl,", 4)) {
  		brl_options = "";
  		str += 4;
  	} else if (!memcmp(str, "brl=", 4)) {
  		brl_options = str + 4;
  		str = strchr(brl_options, ',');
  		if (!str) {
  			printk(KERN_ERR "need port name after brl=
  ");
  			return 1;
  		}
  		*(str++) = 0;
  	}
  #endif

  	/*
  	 * Decode str into name, index, options.
  	 */
  	if (str[0] >= '0' && str[0] <= '9') {

  		strcpy(buf, "ttyS");
  		strncpy(buf + 4, str, sizeof(buf) - 5);

  	} else {

  		strncpy(buf, str, sizeof(buf) - 1);

  	}

  	buf[sizeof(buf) - 1] = 0;

  	if ((options = strchr(str, ',')) != NULL)
  		*(options++) = 0;
  #ifdef __sparc__
  	if (!strcmp(str, "ttya"))

  		strcpy(buf, "ttyS0");

  	if (!strcmp(str, "ttyb"))

  		strcpy(buf, "ttyS1");

  #endif

  	for (s = buf; *s; s++)

  		if ((*s >= '0' && *s <= '9') || *s == ',')
  			break;
  	idx = simple_strtoul(s, NULL, 10);
  	*s = 0;

  	__add_preferred_console(buf, idx, options, brl_options);

  	return 1;
  }
  __setup("console=", console_setup);

  /**

   * add_preferred_console - add a device to the list of preferred consoles.

   * @name: device name
   * @idx: device index
   * @options: options for this console

   *
   * The last preferred console added will be used for kernel messages
   * and stdin/out/err for init.  Normally this is used by console_setup
   * above to handle user-supplied console arguments; however it can also
   * be used by arch-specific code either to override the user or more
   * commonly to provide a default console (ie from PROM variables) when
   * the user has not supplied one.
   */

  int add_preferred_console(char *name, int idx, char *options)

  {

  	return __add_preferred_console(name, idx, options, NULL);

  }

  int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)

  {
  	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)
  ");

  	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);
  		call_console_drivers(_con_start, _log_end);
  		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 | 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]
  ",
  		       bootconsole->name, bootconsole->index,
  		       console->name, console->index);
  		unregister_console(bootconsole);

  		console->flags &= ~CON_PRINTBUFFER;

  	} else {
  		printk(KERN_INFO "console [%s%d] enabled
  ",
  		       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
  ",
  				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 one kernel message
   * every printk_ratelimit_jiffies to make a denial-of-service
   * attack impossible.
   */
  int __printk_ratelimit(int ratelimit_jiffies, int ratelimit_burst)
  {

  	return __ratelimit(ratelimit_jiffies, ratelimit_burst);

  }
  EXPORT_SYMBOL(__printk_ratelimit);
  
  /* minimum time in jiffies between messages */

  int printk_ratelimit_jiffies = 5 * HZ;

  
  /* number of messages we send before ratelimiting */
  int printk_ratelimit_burst = 10;
  
  int printk_ratelimit(void)
  {
  	return __printk_ratelimit(printk_ratelimit_jiffies,
  				printk_ratelimit_burst);
  }
  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