printk.c

Kernel code of linux kernel

/*
 *  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
 *     [e-mail]
 * Rewrote bits to get rid of console_lock
 *	01Mar01 Andrew Morton <[e-mail]>
 */

#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 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 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;
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
 * 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;
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 __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.
 */
static 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;
}

/*
 * 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");