/*
   *  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

   */
  
  #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/memblock.h>

  #include <linux/syscalls.h>

  #include <linux/kexec.h>

  #include <linux/kdb.h>

  #include <linux/ratelimit.h>

  #include <linux/kmsg_dump.h>

  #include <linux/syslog.h>

  #include <linux/cpu.h>
  #include <linux/notifier.h>

  #include <linux/rculist.h>

  
  #include <asm/uaccess.h>

  /*
   * Architectures can override it:
   */

  void asmlinkage __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 CONFIG_DEFAULT_MESSAGE_LOGLEVEL

  
  /* 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 DEFINE_SEMAPHORE(console_sem);

  struct console *console_drivers;

  EXPORT_SYMBOL_GPL(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

   * console_unlock();.

   */

  static DEFINE_RAW_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 */

  
  /*

   * If exclusive_console is non-NULL then only this console is to be printed to.
   */
  static struct console *exclusive_console;
  
  /*

   *	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;

  int console_set_on_cmdline;
  EXPORT_SYMBOL(console_set_on_cmdline);

  
  /* 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 saved_console_loglevel = -1;

  #ifdef CONFIG_KEXEC
  /*
   * This appends the listed symbols to /proc/vmcoreinfo
   *
   * /proc/vmcoreinfo is used by various utiilties, like crash and makedumpfile to
   * obtain access to symbols that are otherwise very difficult to locate.  These
   * symbols are specifically used so that utilities can access and extract the
   * dmesg log from a vmcore file after a crash.
   */
  void log_buf_kexec_setup(void)
  {
  	VMCOREINFO_SYMBOL(log_buf);
  	VMCOREINFO_SYMBOL(log_end);
  	VMCOREINFO_SYMBOL(log_buf_len);
  	VMCOREINFO_SYMBOL(logged_chars);
  }
  #endif

  /* requested log_buf_len from kernel cmdline */
  static unsigned long __initdata new_log_buf_len;
  
  /* save requested log_buf_len since it's too early to process it */

  static int __init log_buf_len_setup(char *str)
  {

  	unsigned size = memparse(str, &str);

  
  	if (size)
  		size = roundup_pow_of_two(size);

  	if (size > log_buf_len)
  		new_log_buf_len = size;
  
  	return 0;

  }

  early_param("log_buf_len", log_buf_len_setup);
  
  void __init setup_log_buf(int early)
  {
  	unsigned long flags;
  	unsigned start, dest_idx, offset;
  	char *new_log_buf;
  	int free;
  
  	if (!new_log_buf_len)
  		return;

  	if (early) {
  		unsigned long mem;
  
  		mem = memblock_alloc(new_log_buf_len, PAGE_SIZE);

  		if (!mem)

  			return;
  		new_log_buf = __va(mem);
  	} else {
  		new_log_buf = alloc_bootmem_nopanic(new_log_buf_len);
  	}
  
  	if (unlikely(!new_log_buf)) {
  		pr_err("log_buf_len: %ld bytes not available
  ",
  			new_log_buf_len);
  		return;
  	}

  	raw_spin_lock_irqsave(&logbuf_lock, flags);

  	log_buf_len = new_log_buf_len;
  	log_buf = new_log_buf;
  	new_log_buf_len = 0;
  	free = __LOG_BUF_LEN - log_end;
  
  	offset = start = min(con_start, log_start);
  	dest_idx = 0;
  	while (start != log_end) {
  		unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);
  
  		log_buf[dest_idx] = __log_buf[log_idx_mask];
  		start++;
  		dest_idx++;
  	}
  	log_start -= offset;
  	con_start -= offset;
  	log_end -= offset;

  	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

  
  	pr_info("log_buf_len: %d
  ", log_buf_len);
  	pr_info("early log buf free: %d(%d%%)
  ",
  		free, (free * 100) / __LOG_BUF_LEN);
  }

  #ifdef CONFIG_BOOT_PRINTK_DELAY

  static int boot_delay; /* msecs delay after each printk during bootup */

  static unsigned long long loops_per_msec;	/* based on boot_delay */

  
  static int __init boot_delay_setup(char *str)
  {
  	unsigned long lpj;

  
  	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;

  	pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
  		"HZ: %d, loops_per_msec: %llu
  ",
  		boot_delay, preset_lpj, lpj, HZ, loops_per_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)loops_per_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

  #ifdef CONFIG_SECURITY_DMESG_RESTRICT
  int dmesg_restrict = 1;
  #else
  int dmesg_restrict;
  #endif

  static int syslog_action_restricted(int type)
  {
  	if (dmesg_restrict)
  		return 1;
  	/* Unless restricted, we allow "read all" and "get buffer size" for everybody */
  	return type != SYSLOG_ACTION_READ_ALL && type != SYSLOG_ACTION_SIZE_BUFFER;
  }
  
  static int check_syslog_permissions(int type, bool from_file)
  {
  	/*
  	 * If this is from /proc/kmsg and we've already opened it, then we've
  	 * already done the capabilities checks at open time.
  	 */
  	if (from_file && type != SYSLOG_ACTION_OPEN)
  		return 0;
  
  	if (syslog_action_restricted(type)) {
  		if (capable(CAP_SYSLOG))
  			return 0;
  		/* For historical reasons, accept CAP_SYS_ADMIN too, with a warning */
  		if (capable(CAP_SYS_ADMIN)) {

  			printk_once(KERN_WARNING "%s (%d): "
  				 "Attempt to access syslog with CAP_SYS_ADMIN "
  				 "but no CAP_SYSLOG (deprecated).
  ",
  				 current->comm, task_pid_nr(current));

  			return 0;
  		}
  		return -EPERM;
  	}
  	return 0;
  }

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

  {

  	unsigned i, j, limit, count;

  	int do_clear = 0;
  	char c;

  	int error;

  	error = check_syslog_permissions(type, from_file);
  	if (error)
  		goto out;

  
  	error = security_syslog(type);

  	if (error)
  		return error;
  
  	switch (type) {

  	case SYSLOG_ACTION_CLOSE:	/* Close log */

  		break;

  	case SYSLOG_ACTION_OPEN:	/* Open log */

  		break;

  	case SYSLOG_ACTION_READ:	/* 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;

  		raw_spin_lock_irq(&logbuf_lock);

  		while (!error && (log_start != log_end) && i < len) {
  			c = LOG_BUF(log_start);
  			log_start++;

  			raw_spin_unlock_irq(&logbuf_lock);

  			error = __put_user(c,buf);
  			buf++;
  			i++;
  			cond_resched();

  			raw_spin_lock_irq(&logbuf_lock);

  		}

  		raw_spin_unlock_irq(&logbuf_lock);

  		if (!error)
  			error = i;
  		break;

  	/* Read/clear last kernel messages */
  	case SYSLOG_ACTION_READ_CLEAR:

  		do_clear = 1;

  		/* FALL THRU */

  	/* Read last kernel messages */
  	case SYSLOG_ACTION_READ_ALL:

  		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;

  		raw_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);

  			raw_spin_unlock_irq(&logbuf_lock);

  			error = __put_user(c,&buf[count-1-i]);
  			cond_resched();

  			raw_spin_lock_irq(&logbuf_lock);

  		}

  		raw_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;

  	/* Clear ring buffer */
  	case SYSLOG_ACTION_CLEAR:

  		logged_chars = 0;
  		break;

  	/* Disable logging to console */
  	case SYSLOG_ACTION_CONSOLE_OFF:

  		if (saved_console_loglevel == -1)
  			saved_console_loglevel = console_loglevel;

  		console_loglevel = minimum_console_loglevel;
  		break;

  	/* Enable logging to console */
  	case SYSLOG_ACTION_CONSOLE_ON:

  		if (saved_console_loglevel != -1) {
  			console_loglevel = saved_console_loglevel;
  			saved_console_loglevel = -1;
  		}

  		break;

  	/* Set level of messages printed to console */
  	case SYSLOG_ACTION_CONSOLE_LEVEL:

  		error = -EINVAL;
  		if (len < 1 || len > 8)
  			goto out;
  		if (len < minimum_console_loglevel)
  			len = minimum_console_loglevel;
  		console_loglevel = len;

  		/* Implicitly re-enable logging to console */
  		saved_console_loglevel = -1;

  		error = 0;
  		break;

  	/* Number of chars in the log buffer */
  	case SYSLOG_ACTION_SIZE_UNREAD:

  		error = log_end - log_start;
  		break;

  	/* Size of the log buffer */
  	case SYSLOG_ACTION_SIZE_BUFFER:

  		error = log_buf_len;
  		break;
  	default:
  		error = -EINVAL;
  		break;
  	}
  out:
  	return error;
  }

  SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)

  {

  	return do_syslog(type, buf, len, SYSLOG_FROM_CALL);

  }

  #ifdef	CONFIG_KGDB_KDB
  /* kdb dmesg command needs access to the syslog buffer.  do_syslog()
   * uses locks so it cannot be used during debugging.  Just tell kdb
   * where the start and end of the physical and logical logs are.  This
   * is equivalent to do_syslog(3).
   */
  void kdb_syslog_data(char *syslog_data[4])
  {
  	syslog_data[0] = log_buf;
  	syslog_data[1] = log_buf + log_buf_len;
  	syslog_data[2] = log_buf + log_end -
  		(logged_chars < log_buf_len ? logged_chars : log_buf_len);
  	syslog_data[3] = log_buf + log_end;
  }
  #endif	/* CONFIG_KGDB_KDB */

  /*
   * Call the console drivers on a range of log_buf
   */

  static void __call_console_drivers(unsigned start, unsigned end)

  {
  	struct console *con;

  	for_each_console(con) {

  		if (exclusive_console && con != exclusive_console)
  			continue;

  		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 bool __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);

  module_param(ignore_loglevel, bool, S_IRUGO | S_IWUSR);

  MODULE_PARM_DESC(ignore_loglevel, "ignore loglevel setting, to"
  	"print all kernel messages to the console.");

  /*
   * 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);
  		}
  	}
  }
  
  /*

   * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
   * lower 3 bit are the log level, the rest are the log facility. In case
   * userspace passes usual userspace syslog messages to /dev/kmsg or
   * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
   * to extract the correct log level for in-kernel processing, and not mangle
   * the original value.
   *
   * If a prefix is found, the length of the prefix is returned. If 'level' is
   * passed, it will be filled in with the log level without a possible facility
   * value. If 'special' is passed, the special printk prefix chars are accepted
   * and returned. If no valid header is found, 0 is returned and the passed
   * variables are not touched.
   */
  static size_t log_prefix(const char *p, unsigned int *level, char *special)
  {
  	unsigned int lev = 0;
  	char sp = '\0';
  	size_t len;
  
  	if (p[0] != '<' || !p[1])
  		return 0;
  	if (p[2] == '>') {
  		/* usual single digit level number or special char */
  		switch (p[1]) {
  		case '0' ... '7':
  			lev = p[1] - '0';
  			break;
  		case 'c': /* KERN_CONT */
  		case 'd': /* KERN_DEFAULT */
  			sp = p[1];
  			break;
  		default:
  			return 0;
  		}
  		len = 3;
  	} else {
  		/* multi digit including the level and facility number */
  		char *endp = NULL;

  		lev = (simple_strtoul(&p[1], &endp, 10) & 7);
  		if (endp == NULL || endp[0] != '>')
  			return 0;
  		len = (endp + 1) - p;
  	}
  
  	/* do not accept special char if not asked for */
  	if (sp && !special)
  		return 0;
  
  	if (special) {
  		*special = sp;
  		/* return special char, do not touch level */
  		if (sp)
  			return len;
  	}
  
  	if (level)
  		*level = lev;
  	return len;
  }
  
  /*

   * Call the console drivers, asking them to write out
   * log_buf[start] to log_buf[end - 1].

   * The console_lock 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)) {
  			/* strip log prefix */
  			cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);

  			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;

  	debug_locks_off();

  	/* If a crash is occurring, make sure we can't deadlock */

  	raw_spin_lock_init(&logbuf_lock);

  	/* And make sure that we print immediately */

  	sema_init(&console_sem, 1);

  }
  
  #if defined(CONFIG_PRINTK_TIME)

  static bool printk_time = 1;

  #else

  static bool 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_each_console(con)

  		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.

   *

   * We try to grab the console_lock.  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 console_unlock(); and will send it to the
   * consoles before releasing the lock.

   *
   * 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)

   *
   * See the vsnprintf() documentation for format string extensions over C99.

   */

  asmlinkage int printk(const char *fmt, ...)
  {
  	va_list args;
  	int r;

  #ifdef CONFIG_KGDB_KDB
  	if (unlikely(kdb_trap_printk)) {
  		va_start(args, fmt);
  		r = vkdb_printf(fmt, args);
  		va_end(args);
  		return r;
  	}
  #endif

  	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_lock 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 console_trylock_for_printk(unsigned int cpu)

  	__releases(&logbuf_lock)

  {

  	int retval = 0, wake = 0;

  	if (console_trylock()) {

  		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;

  			wake = 1;

  			retval = 0;
  		}
  	}

  	printk_cpu = UINT_MAX;

  	if (wake)
  		up(&console_sem);

  	raw_spin_unlock(&logbuf_lock);

  	return retval;
  }

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

  static int new_text_line = 1;

  static char printk_buf[1024];

  int printk_delay_msec __read_mostly;
  
  static inline void printk_delay(void)
  {
  	if (unlikely(printk_delay_msec)) {
  		int m = printk_delay_msec;
  
  		while (m--) {
  			mdelay(1);
  			touch_nmi_watchdog();
  		}
  	}
  }

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

  	int printed_len = 0;

  	int current_log_level = default_message_loglevel;

  	unsigned long flags;

  	int this_cpu;

  	char *p;

  	size_t plen;
  	char special;

  	boot_delay_msec();

  	printk_delay();

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

  	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 && !lockdep_recursing(current)) {

  			recursion_bug = 1;

  			goto out_restore_irqs;
  		}
  		zap_locks();
  	}

  	lockdep_off();

  	raw_spin_lock(&logbuf_lock);

  	printk_cpu = this_cpu;

  	if (recursion_bug) {
  		recursion_bug = 0;
  		strcpy(printk_buf, recursion_bug_msg);

  		printed_len = strlen(recursion_bug_msg);

  	}

  	/* Emit the output into the temporary buffer */

  	printed_len += vscnprintf(printk_buf + printed_len,

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

  	p = printk_buf;

  	/* Read log level and handle special printk prefix */
  	plen = log_prefix(p, &current_log_level, &special);
  	if (plen) {
  		p += plen;
  
  		switch (special) {
  		case 'c': /* Strip <c> KERN_CONT, continue line */
  			plen = 0;
  			break;
  		case 'd': /* Strip <d> KERN_DEFAULT, start new line */
  			plen = 0;
  		default:
  			if (!new_text_line) {
  				emit_log_char('
  ');
  				new_text_line = 1;

  			}
  		}
  	}

  	/*

  	 * Copy the output into log_buf. If the caller didn't provide
  	 * the appropriate log prefix, we insert them here

  	 */

  	for (; *p; p++) {

  		if (new_text_line) {

  			new_text_line = 0;

  			if (plen) {
  				/* Copy original log prefix */
  				int i;
  
  				for (i = 0; i < plen; i++)
  					emit_log_char(printk_buf[i]);
  				printed_len += plen;
  			} else {
  				/* Add log prefix */
  				emit_log_char('<');
  				emit_log_char(current_log_level + '0');
  				emit_log_char('>');
  				printed_len += 3;
  			}

  			if (printk_time) {

  				/* Add the current time stamp */

  				char tbuf[50], *tp;
  				unsigned tlen;
  				unsigned long long t;
  				unsigned long nanosec_rem;

  				t = cpu_clock(printk_cpu);

  				nanosec_rem = do_div(t, 1000000000);

  				tlen = sprintf(tbuf, "[%5lu.%06lu] ",
  						(unsigned long) t,
  						nanosec_rem / 1000);

  
  				for (tp = tbuf; tp < tbuf + tlen; tp++)
  					emit_log_char(*tp);

  				printed_len += tlen;

  			}

  			if (!*p)
  				break;
  		}

  		emit_log_char(*p);
  		if (*p == '
  ')

  			new_text_line = 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 console_trylock_for_printk() function

  	 * will release 'logbuf_lock' regardless of whether it
  	 * actually gets the semaphore or not.
  	 */

  	if (console_trylock_for_printk(this_cpu))
  		console_unlock();

  	lockdep_on();

  out_restore_irqs:

  	local_irq_restore(flags);

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

  #else

  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);

  	console_set_on_cmdline = 1;

  	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;
  }

  bool 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);

  module_param_named(console_suspend, console_suspend_enabled,
  		bool, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
  	" and hibernate operations");

  /**

   * 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)
  ");

  	console_lock();

  	console_suspended = 1;

  	up(&console_sem);

  }
  
  void resume_console(void)
  {

  	if (!console_suspend_enabled)
  		return;

  	down(&console_sem);

  	console_suspended = 0;

  	console_unlock();

  }
  
  /**

   * console_cpu_notify - print deferred console messages after CPU hotplug
   * @self: notifier struct
   * @action: CPU hotplug event
   * @hcpu: unused
   *
   * If printk() is called from a CPU that is not online yet, the messages
   * will be spooled but will not show up on the console.  This function is
   * called when a new CPU comes online (or fails to come up), and ensures
   * that any such output gets printed.
   */
  static int __cpuinit console_cpu_notify(struct notifier_block *self,
  	unsigned long action, void *hcpu)
  {
  	switch (action) {
  	case CPU_ONLINE:
  	case CPU_DEAD:
  	case CPU_DYING:
  	case CPU_DOWN_FAILED:
  	case CPU_UP_CANCELED:

  		console_lock();
  		console_unlock();

  	}
  	return NOTIFY_OK;
  }
  
  /**

   * console_lock - lock the console system for exclusive use.

   *

   * Acquires a lock which guarantees that the caller has

   * exclusive access to the console system and the console_drivers list.
   *
   * Can sleep, returns nothing.
   */

  void console_lock(void)

  {

  	BUG_ON(in_interrupt());

  	down(&console_sem);

  	if (console_suspended)
  		return;

  	console_locked = 1;
  	console_may_schedule = 1;
  }

  EXPORT_SYMBOL(console_lock);

  /**
   * console_trylock - try to lock the console system for exclusive use.
   *
   * Tried to acquire a lock which guarantees that the caller has
   * exclusive access to the console system and the console_drivers list.
   *
   * returns 1 on success, and 0 on failure to acquire the lock.
   */
  int console_trylock(void)

  {
  	if (down_trylock(&console_sem))

  		return 0;

  	if (console_suspended) {
  		up(&console_sem);

  		return 0;

  	}

  	console_locked = 1;
  	console_may_schedule = 0;

  	return 1;

  }

  EXPORT_SYMBOL(console_trylock);

  
  int is_console_locked(void)
  {
  	return console_locked;
  }

  static DEFINE_PER_CPU(int, printk_pending);
  
  void printk_tick(void)

  {

  	if (__this_cpu_read(printk_pending)) {
  		__this_cpu_write(printk_pending, 0);

  		wake_up_interruptible(&log_wait);

  	}
  }
  
  int printk_needs_cpu(int cpu)
  {

  	if (cpu_is_offline(cpu))

  		printk_tick();

  	return __this_cpu_read(printk_pending);

  }
  
  void wake_up_klogd(void)
  {
  	if (waitqueue_active(&log_wait))

  		this_cpu_write(printk_pending, 1);

  }

  /**

   * console_unlock - unlock the console system

   *

   * Releases the console_lock which the caller holds on the console system

   * and the console driver list.
   *

   * While the console_lock was held, console output may have been buffered
   * by printk().  If this is the case, console_unlock(); emits
   * the output prior to releasing the lock.

   *
   * If there is output waiting for klogd, we wake it up.
   *

   * console_unlock(); may be called from any context.

   */

  void console_unlock(void)

  {
  	unsigned long flags;

  	unsigned _con_start, _log_end;

  	unsigned wake_klogd = 0, retry = 0;

  	if (console_suspended) {

  		up(&console_sem);

  		return;
  	}

  
  	console_may_schedule = 0;

  again:

  	for ( ; ; ) {

  		raw_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 */

  		raw_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;

  
  	/* Release the exclusive_console once it is used */
  	if (unlikely(exclusive_console))
  		exclusive_console = NULL;

  	raw_spin_unlock(&logbuf_lock);

  	up(&console_sem);

  
  	/*
  	 * Someone could have filled up the buffer again, so re-check if there's
  	 * something to flush. In case we cannot trylock the console_sem again,
  	 * there's a new owner and the console_unlock() from them will do the
  	 * flush, no worries.
  	 */

  	raw_spin_lock(&logbuf_lock);

  	if (con_start != log_end)
  		retry = 1;

  	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

  	if (retry && console_trylock())
  		goto again;

  	if (wake_klogd)
  		wake_up_klogd();

  }

  EXPORT_SYMBOL(console_unlock);

  /**
   * 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 console_lock();.

   */
  void __sched console_conditional_schedule(void)
  {
  	if (console_may_schedule)
  		cond_resched();
  }
  EXPORT_SYMBOL(console_conditional_schedule);

  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

  		console_lock();

  
  	console_locked = 1;
  	console_may_schedule = 0;

  	for_each_console(c)

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

  	console_unlock();

  }

  
  /*
   * 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;

  	console_lock();

  	for_each_console(c) {

  		if (!c->device)
  			continue;
  		driver = c->device(c, index);
  		if (driver)
  			break;
  	}

  	console_unlock();

  	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)
  {

  	console_lock();

  	console->flags &= ~CON_ENABLED;

  	console_unlock();

  }
  EXPORT_SYMBOL(console_stop);
  
  void console_start(struct console *console)
  {

  	console_lock();

  	console->flags |= CON_ENABLED;

  	console_unlock();

  }
  EXPORT_SYMBOL(console_start);

  static int __read_mostly keep_bootcon;
  
  static int __init keep_bootcon_setup(char *str)
  {
  	keep_bootcon = 1;
  	printk(KERN_INFO "debug: skip boot console de-registration.
  ");
  
  	return 0;
  }
  
  early_param("keep_bootcon", keep_bootcon_setup);

  /*
   * 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.

   *
   * 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 *newcon)

  {

  	int i;

  	unsigned long flags;

  	struct console *bcon = NULL;

  	/*
  	 * 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
  ",
  					newcon->name, newcon->index);
  				return;
  			}
  		}

  	}

  	if (console_drivers && console_drivers->flags & CON_BOOT)
  		bcon = console_drivers;
  
  	if (preferred_console < 0 || bcon || !console_drivers)

  		preferred_console = selected_console;

  	if (newcon->early_setup)
  		newcon->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 (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;
  			}

  		}
  	}
  
  	/*
  	 *	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, newcon->name) != 0)

  			continue;

  		if (newcon->index >= 0 &&
  		    newcon->index != console_cmdline[i].index)

  			continue;

  		if (newcon->index < 0)
  			newcon->index = console_cmdline[i].index;

  #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
  		if (console_cmdline[i].brl_options) {

  			newcon->flags |= CON_BRL;
  			braille_register_console(newcon,

  					console_cmdline[i].index,
  					console_cmdline[i].options,
  					console_cmdline[i].brl_options);
  			return;
  		}
  #endif

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

  			break;

  		newcon->flags |= CON_ENABLED;
  		newcon->index = console_cmdline[i].index;

  		if (i == selected_console) {

  			newcon->flags |= CON_CONSDEV;

  			preferred_console = selected_console;
  		}

  		break;
  	}

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

  		return;

  	/*
  	 * If we have a bootconsole, and are switching to a real console,
  	 * don't print everything out again, since when the boot console, and
  	 * the real console are the same physical device, it's annoying to
  	 * see the beginning boot messages twice
  	 */
  	if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))

  		newcon->flags &= ~CON_PRINTBUFFER;

  
  	/*
  	 *	Put this console in the list - keep the
  	 *	preferred driver at the head of the list.
  	 */

  	console_lock();

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

  	} else {

  		newcon->next = console_drivers->next;
  		console_drivers->next = newcon;

  	}

  	if (newcon->flags & CON_PRINTBUFFER) {

  		/*

  		 * console_unlock(); will print out the buffered messages

  		 * for us.
  		 */

  		raw_spin_lock_irqsave(&logbuf_lock, flags);

  		con_start = log_start;

  		raw_spin_unlock_irqrestore(&logbuf_lock, flags);

  		/*
  		 * We're about to replay the log buffer.  Only do this to the
  		 * just-registered console to avoid excessive message spam to
  		 * the already-registered consoles.
  		 */
  		exclusive_console = newcon;

  	}

  	console_unlock();

  	console_sysfs_notify();

  
  	/*
  	 * By unregistering the bootconsoles after we enable the real console
  	 * we get the "console xxx enabled" message on all the consoles -
  	 * boot consoles, real consoles, etc - this is to ensure that end
  	 * users know there might be something in the kernel's log buffer that
  	 * went to the bootconsole (that they do not see on the real console)
  	 */

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

  		/* we need to iterate through twice, to make sure we print
  		 * everything out, before we unregister the console(s)
  		 */
  		printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled
  ",
  			newcon->name, newcon->index);
  		for_each_console(bcon)
  			if (bcon->flags & CON_BOOT)
  				unregister_console(bcon);
  	} else {
  		printk(KERN_INFO "%sconsole [%s%d] enabled
  ",
  			(newcon->flags & CON_BOOT) ? "boot" : "" ,
  			newcon->name, newcon->index);
  	}

  }
  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

  	console_lock();

  	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;

  	console_unlock();

  	console_sysfs_notify();

  	return res;
  }
  EXPORT_SYMBOL(unregister_console);

  static int __init printk_late_init(void)

  {

  	struct console *con;
  
  	for_each_console(con) {

  		if (!keep_bootcon && con->flags & CON_BOOT) {

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

  				con->name, con->index);

  			unregister_console(con);

  		}

  	}

  	hotcpu_notifier(console_cpu_notify, 0);

  	return 0;
  }

  late_initcall(printk_late_init);

  #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(const char *func)

  {

  	return ___ratelimit(&printk_ratelimit_state, func);

  }

  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_in_range(jiffies, *caller_jiffies,
  					*caller_jiffies
  					+ msecs_to_jiffies(interval_msecs))) {
  		*caller_jiffies = jiffies;

  		return true;
  	}
  	return false;
  }
  EXPORT_SYMBOL(printk_timed_ratelimit);

  
  static DEFINE_SPINLOCK(dump_list_lock);
  static LIST_HEAD(dump_list);
  
  /**
   * kmsg_dump_register - register a kernel log dumper.

   * @dumper: pointer to the kmsg_dumper structure

   *
   * Adds a kernel log dumper to the system. The dump callback in the
   * structure will be called when the kernel oopses or panics and must be
   * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
   */
  int kmsg_dump_register(struct kmsg_dumper *dumper)
  {
  	unsigned long flags;
  	int err = -EBUSY;
  
  	/* The dump callback needs to be set */
  	if (!dumper->dump)
  		return -EINVAL;
  
  	spin_lock_irqsave(&dump_list_lock, flags);
  	/* Don't allow registering multiple times */
  	if (!dumper->registered) {
  		dumper->registered = 1;

  		list_add_tail_rcu(&dumper->list, &dump_list);

  		err = 0;
  	}
  	spin_unlock_irqrestore(&dump_list_lock, flags);
  
  	return err;
  }
  EXPORT_SYMBOL_GPL(kmsg_dump_register);
  
  /**
   * kmsg_dump_unregister - unregister a kmsg dumper.

   * @dumper: pointer to the kmsg_dumper structure

   *
   * Removes a dump device from the system. Returns zero on success and
   * %-EINVAL otherwise.
   */
  int kmsg_dump_unregister(struct kmsg_dumper *dumper)
  {
  	unsigned long flags;
  	int err = -EINVAL;
  
  	spin_lock_irqsave(&dump_list_lock, flags);
  	if (dumper->registered) {
  		dumper->registered = 0;

  		list_del_rcu(&dumper->list);

  		err = 0;
  	}
  	spin_unlock_irqrestore(&dump_list_lock, flags);

  	synchronize_rcu();

  
  	return err;
  }
  EXPORT_SYMBOL_GPL(kmsg_dump_unregister);

  /**
   * kmsg_dump - dump kernel log to kernel message dumpers.
   * @reason: the reason (oops, panic etc) for dumping
   *
   * Iterate through each of the dump devices and call the oops/panic
   * callbacks with the log buffer.
   */
  void kmsg_dump(enum kmsg_dump_reason reason)
  {
  	unsigned long end;
  	unsigned chars;
  	struct kmsg_dumper *dumper;
  	const char *s1, *s2;
  	unsigned long l1, l2;
  	unsigned long flags;
  
  	/* Theoretically, the log could move on after we do this, but
  	   there's not a lot we can do about that. The new messages
  	   will overwrite the start of what we dump. */

  	raw_spin_lock_irqsave(&logbuf_lock, flags);

  	end = log_end & LOG_BUF_MASK;
  	chars = logged_chars;

  	raw_spin_unlock_irqrestore(&logbuf_lock, flags);

  	if (chars > end) {
  		s1 = log_buf + log_buf_len - chars + end;
  		l1 = chars - end;

  
  		s2 = log_buf;
  		l2 = end;
  	} else {
  		s1 = "";
  		l1 = 0;

  		s2 = log_buf + end - chars;
  		l2 = chars;

  	}

  	rcu_read_lock();
  	list_for_each_entry_rcu(dumper, &dump_list, list)

  		dumper->dump(dumper, reason, s1, l1, s2, l2);

  	rcu_read_unlock();

  }

  #endif