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printk.c

/*
 *  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 <linux/jiffies.h>

#include <asm/uaccess.h>

#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 long log_start;     /* Index into log_buf: next char to be read by syslog() */
static unsigned long con_start;     /* Index into log_buf: next char to be sent to consoles */
static unsigned long 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   */
};

#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 long logged_chars; /* Number of chars produced since last read+clear operation */

static int __init log_buf_len_setup(char *str)
{
      unsigned long size = memparse(str, &str);
      unsigned long flags;

      if (size)
            size = roundup_pow_of_two(size);
      if (size > log_buf_len) {
            unsigned long 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 long 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 long start, unsigned long 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 1;
}

__setup("ignore_loglevel", ignore_loglevel_setup);

/*
 * Write out chars from start to end - 1 inclusive
 */
static void _call_console_drivers(unsigned long start,
                        unsigned long 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 long start, unsigned long end)
{
      unsigned long cur_index, start_print;
      static int msg_level = -1;

      BUG_ON(((long)(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);

static int __init printk_time_setup(char *str)
{
      if (*str)
            return 0;
      printk_time = 1;
      printk(KERN_NOTICE "The 'time' option is deprecated and "
            "is scheduled for removal in early 2008\n");
      printk(KERN_NOTICE "Use 'printk.time=<value>' instead\n");
      return 1;
}

__setup("time", printk_time_setup);

__attribute__((weak)) unsigned long long printk_clock(void)
{
      return sched_clock();
}

/* 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;

asmlinkage int vprintk(const char *fmt, va_list args)
{
      unsigned long flags;
      int printed_len;
      char *p;
      static char printk_buf[1024];
      static int log_level_unknown = 1;

      boot_delay_msec();

      preempt_disable();
      if (unlikely(oops_in_progress) && printk_cpu == smp_processor_id())
            /* If a crash is occurring during printk() on this CPU,
             * make sure we can't deadlock */
            zap_locks();

      /* This stops the holder of console_sem just where we want him */
      raw_local_irq_save(flags);
      lockdep_off();
      spin_lock(&logbuf_lock);
      printk_cpu = smp_processor_id();

      /* Emit the output into the temporary buffer */
      printed_len = vscnprintf(printk_buf, sizeof(printk_buf), 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 = printk_clock();
                        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;
      }

      if (!down_trylock(&console_sem)) {
            /*
             * We own the drivers.  We can drop the spinlock and
             * let release_console_sem() print the text, maybe ...
             */
            console_locked = 1;
            printk_cpu = UINT_MAX;
            spin_unlock(&logbuf_lock);

            /*
             * 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.
             */
            if (cpu_online(smp_processor_id()) || have_callable_console()) {
                  console_may_schedule = 0;
                  release_console_sem();
            } else {
                  /* Release by hand to avoid flushing the buffer. */
                  console_locked = 0;
                  up(&console_sem);
            }
            lockdep_on();
            raw_local_irq_restore(flags);
      } else {
            /*
             * Someone else owns the drivers.  We drop the spinlock, which
             * allows the semaphore holder to proceed and to call the
             * console drivers with the output which we just produced.
             */
            printk_cpu = UINT_MAX;
            spin_unlock(&logbuf_lock);
            lockdep_on();
            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 long start, unsigned long end)
{
}

#endif

/*
 * 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;
      int idx;

      /*
       * 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);
      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)
{
      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) {
                        selected_console = i;
                        return 0;
            }
      if (i == MAX_CMDLINECONSOLES)
            return -E2BIG;
      selected_console = i;
      c = &console_cmdline[i];
      memcpy(c->name, name, sizeof(c->name));
      c->name[sizeof(c->name) - 1] = 0;
      c->options = options;
      c->index = idx;
      return 0;
}

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 long _con_start, _log_end;
      unsigned long 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;
            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;

      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->driver->write)
            tty->driver->write(tty, msg, strlen(msg));
      return;
}

/*
 * 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)
{
      static DEFINE_SPINLOCK(ratelimit_lock);
      static unsigned long toks = 10 * 5 * HZ;
      static unsigned long last_msg;
      static int missed;
      unsigned long flags;
      unsigned long now = jiffies;

      spin_lock_irqsave(&ratelimit_lock, flags);
      toks += now - last_msg;
      last_msg = now;
      if (toks > (ratelimit_burst * ratelimit_jiffies))
            toks = ratelimit_burst * ratelimit_jiffies;
      if (toks >= ratelimit_jiffies) {
            int lost = missed;

            missed = 0;
            toks -= ratelimit_jiffies;
            spin_unlock_irqrestore(&ratelimit_lock, flags);
            if (lost)
                  printk(KERN_WARNING "printk: %d messages suppressed.\n", lost);
            return 1;
      }
      missed++;
      spin_unlock_irqrestore(&ratelimit_lock, flags);
      return 0;
}
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);

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