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26 results

printk.c

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  • printk.c 33.29 KiB
    /*
     *  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\n");
    			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\n", 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\n",
    		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.\n");
    
    	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 == '\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++;
    }
    
    /*
     * 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!\n";
    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 == '\n')
    			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=\n");
    			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];
    				memcpy(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)\n");
    	acquire_console_sem();
    	console_suspended = 1;
    }
    
    void resume_console(void)
    {
    	if (!console_suspend_enabled)
    		return;
    	console_suspended = 0;
    	release_console_sem();
    }
    
    /**
     * acquire_console_sem - lock the console system for exclusive use.
     *
     * Acquires a semaphore which guarantees that the caller has
     * exclusive access to the console system and the console_drivers list.
     *
     * Can sleep, returns nothing.
     */
    void acquire_console_sem(void)
    {
    	BUG_ON(in_interrupt());
    	if (console_suspended) {
    		down(&secondary_console_sem);
    		return;
    	}
    	down(&console_sem);
    	console_locked = 1;
    	console_may_schedule = 1;
    }
    EXPORT_SYMBOL(acquire_console_sem);
    
    int try_acquire_console_sem(void)
    {
    	if (down_trylock(&console_sem))
    		return -1;
    	console_locked = 1;
    	console_may_schedule = 0;
    	return 0;
    }
    EXPORT_SYMBOL(try_acquire_console_sem);
    
    int is_console_locked(void)
    {
    	return console_locked;
    }
    
    void wake_up_klogd(void)
    {
    	if (!oops_in_progress && waitqueue_active(&log_wait))
    		wake_up_interruptible(&log_wait);
    }
    
    /**
     * release_console_sem - unlock the console system
     *
     * Releases the semaphore which the caller holds on the console system
     * and the console driver list.
     *
     * While the semaphore was held, console output may have been buffered
     * by printk().  If this is the case, release_console_sem() emits
     * the output prior to releasing the semaphore.
     *
     * If there is output waiting for klogd, we wake it up.
     *
     * release_console_sem() may be called from any context.
     */
    void release_console_sem(void)
    {
    	unsigned long flags;
    	unsigned _con_start, _log_end;
    	unsigned wake_klogd = 0;
    
    	if (console_suspended) {
    		up(&secondary_console_sem);
    		return;
    	}
    
    	console_may_schedule = 0;
    
    	for ( ; ; ) {
    		spin_lock_irqsave(&logbuf_lock, flags);
    		wake_klogd |= log_start - log_end;
    		if (con_start == log_end)
    			break;			/* Nothing to print */
    		_con_start = con_start;
    		_log_end = log_end;
    		con_start = log_end;		/* Flush */
    		spin_unlock(&logbuf_lock);
    		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]\n",
    		       bootconsole->name, bootconsole->index,
    		       console->name, console->index);
    		unregister_console(bootconsole);
    		console->flags &= ~CON_PRINTBUFFER;
    	} else {
    		printk(KERN_INFO "console [%s%d] enabled\n",
    		       console->name, console->index);
    	}
    
    	/*
    	 *	Put this console in the list - keep the
    	 *	preferred driver at the head of the list.
    	 */
    	acquire_console_sem();
    	if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
    		console->next = console_drivers;
    		console_drivers = console;
    		if (console->next)
    			console->next->flags &= ~CON_CONSDEV;
    	} else {
    		console->next = console_drivers->next;
    		console_drivers->next = console;
    	}
    	if (console->flags & CON_PRINTBUFFER) {
    		/*
    		 * release_console_sem() will print out the buffered messages
    		 * for us.
    		 */
    		spin_lock_irqsave(&logbuf_lock, flags);
    		con_start = log_start;
    		spin_unlock_irqrestore(&logbuf_lock, flags);
    	}
    	release_console_sem();
    }
    EXPORT_SYMBOL(register_console);
    
    int unregister_console(struct console *console)
    {
            struct console *a, *b;
    	int res = 1;
    
    #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
    	if (console->flags & CON_BRL)
    		return braille_unregister_console(console);
    #endif
    
    	acquire_console_sem();
    	if (console_drivers == console) {
    		console_drivers=console->next;
    		res = 0;
    	} else if (console_drivers) {
    		for (a=console_drivers->next, b=console_drivers ;
    		     a; b=a, a=b->next) {
    			if (a == console) {
    				b->next = a->next;
    				res = 0;
    				break;
    			}
    		}
    	}
    
    	/*
    	 * If this isn't the last console and it has CON_CONSDEV set, we
    	 * need to set it on the next preferred console.
    	 */
    	if (console_drivers != NULL && console->flags & CON_CONSDEV)
    		console_drivers->flags |= CON_CONSDEV;
    
    	release_console_sem();
    	return res;
    }
    EXPORT_SYMBOL(unregister_console);
    
    static int __init disable_boot_consoles(void)
    {
    	if (console_drivers != NULL) {
    		if (console_drivers->flags & CON_BOOT) {
    			printk(KERN_INFO "turn off boot console %s%d\n",
    				console_drivers->name, console_drivers->index);
    			return unregister_console(console_drivers);
    		}
    	}
    	return 0;
    }
    late_initcall(disable_boot_consoles);
    
    /**
     * tty_write_message - write a message to a certain tty, not just the console.
     * @tty: the destination tty_struct
     * @msg: the message to write
     *
     * This is used for messages that need to be redirected to a specific tty.
     * We don't put it into the syslog queue right now maybe in the future if
     * really needed.
     */
    void tty_write_message(struct tty_struct *tty, char *msg)
    {
    	if (tty && tty->ops->write)
    		tty->ops->write(tty, msg, strlen(msg));
    	return;
    }
    
    #if defined CONFIG_PRINTK
    /*
     * printk rate limiting, lifted from the networking subsystem.
     *
     * This enforces a rate limit: not more than 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