printk.c

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/*
 *  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
 *     [email protected]
 * 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 <linux/poll.h>

#include <asm/uaccess.h>

#define CREATE_TRACE_POINTS
#include <trace/events/printk.h>

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

/* 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;

/*
 * 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;

/*
 * The printk log buffer consists of a chain of concatenated variable
 * length records. Every record starts with a record header, containing
 * the overall length of the record.
 *
 * The heads to the first and last entry in the buffer, as well as the
 * sequence numbers of these both entries are maintained when messages
 * are stored..
 *
 * If the heads indicate available messages, the length in the header
 * tells the start next message. A length == 0 for the next message
 * indicates a wrap-around to the beginning of the buffer.
 *
 * Every record carries the monotonic timestamp in microseconds, as well as
 * the standard userspace syslog level and syslog facility. The usual
 * kernel messages use LOG_KERN; userspace-injected messages always carry
 * a matching syslog facility, by default LOG_USER. The origin of every
 * message can be reliably determined that way.
 *
 * The human readable log message directly follows the message header. The
 * length of the message text is stored in the header, the stored message
 * is not terminated.
 *
 * Optionally, a message can carry a dictionary of properties (key/value pairs),
 * to provide userspace with a machine-readable message context.
 *
 * Examples for well-defined, commonly used property names are:
 *   DEVICE=b12:8               device identifier
 *                                b12:8         block dev_t
 *                                c127:3        char dev_t
 *                                n8            netdev ifindex
 *                                +sound:card0  subsystem:devname
 *   SUBSYSTEM=pci              driver-core subsystem name
 *
 * Valid characters in property names are [a-zA-Z0-9.-_]. The plain text value
 * follows directly after a '=' character. Every property is terminated by
 * a '\0' character. The last property is not terminated.
 *
 * Example of a message structure:
 *   0000  ff 8f 00 00 00 00 00 00      monotonic time in nsec
 *   0008  34 00                        record is 52 bytes long
 *   000a        0b 00                  text is 11 bytes long
 *   000c              1f 00            dictionary is 23 bytes long
 *   000e                    03 00      LOG_KERN (facility) LOG_ERR (level)
 *   0010  69 74 27 73 20 61 20 6c      "it's a l"
 *         69 6e 65                     "ine"
 *   001b           44 45 56 49 43      "DEVIC"
 *         45 3d 62 38 3a 32 00 44      "E=b8:2\0D"
 *         52 49 56 45 52 3d 62 75      "RIVER=bu"
 *         67                           "g"
 *   0032     00 00 00                  padding to next message header
 *
 * The 'struct log' buffer header must never be directly exported to
 * userspace, it is a kernel-private implementation detail that might
 * need to be changed in the future, when the requirements change.
 *
 * /dev/kmsg exports the structured data in the following line format:
 *   "level,sequnum,timestamp;<message text>\n"
 *
 * The optional key/value pairs are attached as continuation lines starting
 * with a space character and terminated by a newline. All possible
 * non-prinatable characters are escaped in the "\xff" notation.
 *
 * Users of the export format should ignore possible additional values
 * separated by ',', and find the message after the ';' character.
 */

enum log_flags {
    LOG_NOCONS  = 1,    /* already flushed, do not print to console */
    LOG_NEWLINE = 2,    /* text ended with a newline */
    LOG_PREFIX  = 4,    /* text started with a prefix */
    LOG_CONT    = 8,    /* text is a fragment of a continuation line */
};

struct log {
    u64 ts_nsec;        /* timestamp in nanoseconds */
    u16 len;        /* length of entire record */
    u16 text_len;       /* length of text buffer */
    u16 dict_len;       /* length of dictionary buffer */
    u8 facility;        /* syslog facility */
    u8 flags:5;     /* internal record flags */
    u8 level:3;     /* syslog level */
};

/*
 * The logbuf_lock protects kmsg buffer, indices, counters. It is also
 * used in interesting ways to provide interlocking in console_unlock();
 */
static DEFINE_RAW_SPINLOCK(logbuf_lock);

#ifdef CONFIG_PRINTK
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static u32 syslog_idx;
static enum log_flags syslog_prev;
static size_t syslog_partial;

/* index and sequence number of the first record stored in the buffer */
static u64 log_first_seq;
static u32 log_first_idx;

/* index and sequence number of the next record to store in the buffer */
static u64 log_next_seq;
static u32 log_next_idx;

/* the next printk record to write to the console */
static u64 console_seq;
static u32 console_idx;
static enum log_flags console_prev;

/* the next printk record to read after the last 'clear' command */
static u64 clear_seq;
static u32 clear_idx;

#define PREFIX_MAX      32
#define LOG_LINE_MAX        1024 - PREFIX_MAX

/* record buffer */
#if defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
#define LOG_ALIGN 4
#else
#define LOG_ALIGN __alignof__(struct log)
#endif
#define __LOG_BUF_LEN (1 << CONFIG_LOG_BUF_SHIFT)
static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;

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

/* human readable text of the record */
static char *log_text(const struct log *msg)
{
    return (char *)msg + sizeof(struct log);
}

/* optional key/value pair dictionary attached to the record */
static char *log_dict(const struct log *msg)
{
    return (char *)msg + sizeof(struct log) + msg->text_len;
}

/* get record by index; idx must point to valid msg */
static struct log *log_from_idx(u32 idx)
{
    struct log *msg = (struct log *)(log_buf + idx);

    /*
     * A length == 0 record is the end of buffer marker. Wrap around and
     * read the message at the start of the buffer.
     */
    if (!msg->len)
        return (struct log *)log_buf;
    return msg;
}

/* get next record; idx must point to valid msg */
static u32 log_next(u32 idx)
{
    struct log *msg = (struct log *)(log_buf + idx);

    /* length == 0 indicates the end of the buffer; wrap */
    /*
     * A length == 0 record is the end of buffer marker. Wrap around and
     * read the message at the start of the buffer as *this* one, and
     * return the one after that.
     */
    if (!msg->len) {
        msg = (struct log *)log_buf;
        return msg->len;
    }
    return idx + msg->len;
}

/* insert record into the buffer, discard old ones, update heads */
static void log_store(int facility, int level,
              enum log_flags flags, u64 ts_nsec,
              const char *dict, u16 dict_len,
              const char *text, u16 text_len)
{
    struct log *msg;
    u32 size, pad_len;

    /* number of '\0' padding bytes to next message */
    size = sizeof(struct log) + text_len + dict_len;
    pad_len = (-size) & (LOG_ALIGN - 1);
    size += pad_len;

    while (log_first_seq < log_next_seq) {
        u32 free;

        if (log_next_idx > log_first_idx)
            free = max(log_buf_len - log_next_idx, log_first_idx);
        else
            free = log_first_idx - log_next_idx;

        if (free > size + sizeof(struct log))
            break;

        /* drop old messages until we have enough contiuous space */
        log_first_idx = log_next(log_first_idx);
        log_first_seq++;
    }

    if (log_next_idx + size + sizeof(struct log) >= log_buf_len) {
        /*
         * This message + an additional empty header does not fit
         * at the end of the buffer. Add an empty header with len == 0
         * to signify a wrap around.
         */
        memset(log_buf + log_next_idx, 0, sizeof(struct log));
        log_next_idx = 0;
    }

    /* fill message */
    msg = (struct log *)(log_buf + log_next_idx);
    memcpy(log_text(msg), text, text_len);
    msg->text_len = text_len;
    memcpy(log_dict(msg), dict, dict_len);
    msg->dict_len = dict_len;
    msg->facility = facility;
    msg->level = level & 7;
    msg->flags = flags & 0x1f;
    if (ts_nsec > 0)
        msg->ts_nsec = ts_nsec;
    else
        msg->ts_nsec = local_clock();
    memset(log_dict(msg) + dict_len, 0, pad_len);
    msg->len = sizeof(struct log) + text_len + dict_len + pad_len;

    /* insert message */
    log_next_idx += msg->len;
    log_next_seq++;
}

/* /dev/kmsg - userspace message inject/listen interface */
struct devkmsg_user {
    u64 seq;
    u32 idx;
    enum log_flags prev;
    struct mutex lock;
    char buf[8192];
};

static ssize_t devkmsg_writev(struct kiocb *iocb, const struct iovec *iv,
                  unsigned long count, loff_t pos)
{
    char *buf, *line;
    int i;
    int level = default_message_loglevel;
    int facility = 1;   /* LOG_USER */
    size_t len = iov_length(iv, count);
    ssize_t ret = len;

    if (len > LOG_LINE_MAX)
        return -EINVAL;
    buf = kmalloc(len+1, GFP_KERNEL);
    if (buf == NULL)
        return -ENOMEM;

    line = buf;
    for (i = 0; i < count; i++) {
        if (copy_from_user(line, iv[i].iov_base, iv[i].iov_len)) {
            ret = -EFAULT;
            goto out;
        }
        line += iv[i].iov_len;
    }

    /*
     * Extract and skip the syslog prefix <[0-9]*>. Coming from userspace
     * the decimal value represents 32bit, the lower 3 bit are the log
     * level, the rest are the log facility.
     *
     * If no prefix or no userspace facility is specified, we
     * enforce LOG_USER, to be able to reliably distinguish
     * kernel-generated messages from userspace-injected ones.
     */
    line = buf;
    if (line[0] == '<') {
        char *endp = NULL;

        i = simple_strtoul(line+1, &endp, 10);
        if (endp && endp[0] == '>') {
            level = i & 7;
            if (i >> 3)
                facility = i >> 3;
            endp++;
            len -= endp - line;
            line = endp;
        }
    }
    line[len] = '\0';

    printk_emit(facility, level, NULL, 0, "%s", line);
out:
    kfree(buf);
    return ret;
}

static ssize_t devkmsg_read(struct file *file, char __user *buf,
                size_t count, loff_t *ppos)
{
    struct devkmsg_user *user = file->private_data;
    struct log *msg;
    u64 ts_usec;
    size_t i;
    char cont = '-';
    size_t len;
    ssize_t ret;

    if (!user)
        return -EBADF;

    ret = mutex_lock_interruptible(&user->lock);
    if (ret)
        return ret;
    raw_spin_lock_irq(&logbuf_lock);
    while (user->seq == log_next_seq) {
        if (file->f_flags & O_NONBLOCK) {
            ret = -EAGAIN;
            raw_spin_unlock_irq(&logbuf_lock);
            goto out;
        }

        raw_spin_unlock_irq(&logbuf_lock);
        ret = wait_event_interruptible(log_wait,
                           user->seq != log_next_seq);
        if (ret)
            goto out;
        raw_spin_lock_irq(&logbuf_lock);
    }

    if (user->seq < log_first_seq) {
        /* our last seen message is gone, return error and reset */
        user->idx = log_first_idx;
        user->seq = log_first_seq;
        ret = -EPIPE;
        raw_spin_unlock_irq(&logbuf_lock);
        goto out;
    }

    msg = log_from_idx(user->idx);
    ts_usec = msg->ts_nsec;
    do_div(ts_usec, 1000);

    /*
     * If we couldn't merge continuation line fragments during the print,
     * export the stored flags to allow an optional external merge of the
     * records. Merging the records isn't always neccessarily correct, like
     * when we hit a race during printing. In most cases though, it produces
     * better readable output. 'c' in the record flags mark the first
     * fragment of a line, '+' the following.
     */
    if (msg->flags & LOG_CONT && !(user->prev & LOG_CONT))
        cont = 'c';
    else if ((msg->flags & LOG_CONT) ||
         ((user->prev & LOG_CONT) && !(msg->flags & LOG_PREFIX)))
        cont = '+';

    len = sprintf(user->buf, "%u,%llu,%llu,%c;",
              (msg->facility << 3) | msg->level,
              user->seq, ts_usec, cont);
    user->prev = msg->flags;

    /* escape non-printable characters */
    for (i = 0; i < msg->text_len; i++) {
        unsigned char c = log_text(msg)[i];

        if (c < ' ' || c >= 127 || c == '\\')
            len += sprintf(user->buf + len, "\\x%02x", c);
        else
            user->buf[len++] = c;
    }
    user->buf[len++] = '\n';

    if (msg->dict_len) {
        bool line = true;

        for (i = 0; i < msg->dict_len; i++) {
            unsigned char c = log_dict(msg)[i];

            if (line) {
                user->buf[len++] = ' ';
                line = false;
            }

            if (c == '\0') {
                user->buf[len++] = '\n';
                line = true;
                continue;
            }

            if (c < ' ' || c >= 127 || c == '\\') {
                len += sprintf(user->buf + len, "\\x%02x", c);
                continue;
            }

            user->buf[len++] = c;
        }
        user->buf[len++] = '\n';
    }

    user->idx = log_next(user->idx);
    user->seq++;
    raw_spin_unlock_irq(&logbuf_lock);

    if (len > count) {
        ret = -EINVAL;
        goto out;
    }

    if (copy_to_user(buf, user->buf, len)) {
        ret = -EFAULT;
        goto out;
    }
    ret = len;
out:
    mutex_unlock(&user->lock);
    return ret;
}

static loff_t devkmsg_llseek(struct file *file, loff_t offset, int whence)
{
    struct devkmsg_user *user = file->private_data;
    loff_t ret = 0;

    if (!user)
        return -EBADF;
    if (offset)
        return -ESPIPE;

    raw_spin_lock_irq(&logbuf_lock);
    switch (whence) {
    case SEEK_SET:
        /* the first record */
        user->idx = log_first_idx;
        user->seq = log_first_seq;
        break;
    case SEEK_DATA:
        /*
         * The first record after the last SYSLOG_ACTION_CLEAR,
         * like issued by 'dmesg -c'. Reading /dev/kmsg itself
         * changes no global state, and does not clear anything.
         */
        user->idx = clear_idx;
        user->seq = clear_seq;
        break;
    case SEEK_END:
        /* after the last record */
        user->idx = log_next_idx;
        user->seq = log_next_seq;
        break;
    default:
        ret = -EINVAL;
    }
    raw_spin_unlock_irq(&logbuf_lock);
    return ret;
}

static unsigned int devkmsg_poll(struct file *file, poll_table *wait)
{
    struct devkmsg_user *user = file->private_data;
    int ret = 0;

    if (!user)
        return POLLERR|POLLNVAL;

    poll_wait(file, &log_wait, wait);

    raw_spin_lock_irq(&logbuf_lock);
    if (user->seq < log_next_seq) {
        /* return error when data has vanished underneath us */
        if (user->seq < log_first_seq)
            ret = POLLIN|POLLRDNORM|POLLERR|POLLPRI;
        ret = POLLIN|POLLRDNORM;
    }
    raw_spin_unlock_irq(&logbuf_lock);

    return ret;
}

static int devkmsg_open(struct inode *inode, struct file *file)
{
    struct devkmsg_user *user;
    int err;

    /* write-only does not need any file context */
    if ((file->f_flags & O_ACCMODE) == O_WRONLY)
        return 0;

    err = security_syslog(SYSLOG_ACTION_READ_ALL);
    if (err)
        return err;

    user = kmalloc(sizeof(struct devkmsg_user), GFP_KERNEL);
    if (!user)
        return -ENOMEM;

    mutex_init(&user->lock);

    raw_spin_lock_irq(&logbuf_lock);
    user->idx = log_first_idx;
    user->seq = log_first_seq;
    raw_spin_unlock_irq(&logbuf_lock);

    file->private_data = user;
    return 0;
}

static int devkmsg_release(struct inode *inode, struct file *file)
{
    struct devkmsg_user *user = file->private_data;

    if (!user)
        return 0;

    mutex_destroy(&user->lock);
    kfree(user);
    return 0;
}

const struct file_operations kmsg_fops = {
    .open = devkmsg_open,
    .read = devkmsg_read,
    .aio_write = devkmsg_writev,
    .llseek = devkmsg_llseek,
    .poll = devkmsg_poll,
    .release = devkmsg_release,
};

#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_buf_len);
    VMCOREINFO_SYMBOL(log_first_idx);
    VMCOREINFO_SYMBOL(log_next_idx);
    /*
     * Export struct log size and field offsets. User space tools can
     * parse it and detect any changes to structure down the line.
     */
    VMCOREINFO_STRUCT_SIZE(log);
    VMCOREINFO_OFFSET(log, ts_nsec);
    VMCOREINFO_OFFSET(log, len);
    VMCOREINFO_OFFSET(log, text_len);
    VMCOREINFO_OFFSET(log, dict_len);
}
#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;
    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\n",
            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_next_idx;
    memcpy(log_buf, __log_buf, __LOG_BUF_LEN);
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);

    pr_info("log_buf_len: %d\n", log_buf_len);
    pr_info("early log buf free: %d(%d%%)\n",
        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\n",
        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).\n",
                 current->comm, task_pid_nr(current));
            return 0;
        }
        return -EPERM;
    }
    return 0;
}

#if defined(CONFIG_PRINTK_TIME)
static bool printk_time = 1;
#else
static bool printk_time;
#endif
module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);

static size_t print_time(u64 ts, char *buf)
{
    unsigned long rem_nsec;

    if (!printk_time)
        return 0;

    if (!buf)
        return 15;

    rem_nsec = do_div(ts, 1000000000);
    return sprintf(buf, "[%5lu.%06lu] ",
               (unsigned long)ts, rem_nsec / 1000);
}

static size_t print_prefix(const struct log *msg, bool syslog, char *buf)
{
    size_t len = 0;
    unsigned int prefix = (msg->facility << 3) | msg->level;

    if (syslog) {
        if (buf) {
            len += sprintf(buf, "<%u>", prefix);
        } else {
            len += 3;
            if (prefix > 999)
                len += 3;
            else if (prefix > 99)
                len += 2;
            else if (prefix > 9)
                len++;
        }
    }

    len += print_time(msg->ts_nsec, buf ? buf + len : NULL);
    return len;
}

static size_t msg_print_text(const struct log *msg, enum log_flags prev,
                 bool syslog, char *buf, size_t size)
{
    const char *text = log_text(msg);
    size_t text_size = msg->text_len;
    bool prefix = true;
    bool newline = true;
    size_t len = 0;

    if ((prev & LOG_CONT) && !(msg->flags & LOG_PREFIX))
        prefix = false;

    if (msg->flags & LOG_CONT) {
        if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE))
            prefix = false;

        if (!(msg->flags & LOG_NEWLINE))
            newline = false;
    }

    do {
        const char *next = memchr(text, '\n', text_size);
        size_t text_len;

        if (next) {
            text_len = next - text;
            next++;
            text_size -= next - text;
        } else {
            text_len = text_size;
        }

        if (buf) {
            if (print_prefix(msg, syslog, NULL) +
                text_len + 1 >= size - len)
                break;

            if (prefix)
                len += print_prefix(msg, syslog, buf + len);
            memcpy(buf + len, text, text_len);
            len += text_len;
            if (next || newline)
                buf[len++] = '\n';
        } else {
            /* SYSLOG_ACTION_* buffer size only calculation */
            if (prefix)
                len += print_prefix(msg, syslog, NULL);
            len += text_len;
            if (next || newline)
                len++;
        }

        prefix = true;
        text = next;
    } while (text);

    return len;
}

static int syslog_print(char __user *buf, int size)
{
    char *text;
    struct log *msg;
    int len = 0;

    text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
    if (!text)
        return -ENOMEM;

    while (size > 0) {
        size_t n;
        size_t skip;

        raw_spin_lock_irq(&logbuf_lock);
        if (syslog_seq < log_first_seq) {
            /* messages are gone, move to first one */
            syslog_seq = log_first_seq;
            syslog_idx = log_first_idx;
            syslog_prev = 0;
            syslog_partial = 0;
        }
        if (syslog_seq == log_next_seq) {
            raw_spin_unlock_irq(&logbuf_lock);
            break;
        }

        skip = syslog_partial;
        msg = log_from_idx(syslog_idx);
        n = msg_print_text(msg, syslog_prev, true, text,
                   LOG_LINE_MAX + PREFIX_MAX);
        if (n - syslog_partial <= size) {
            /* message fits into buffer, move forward */
            syslog_idx = log_next(syslog_idx);
            syslog_seq++;
            syslog_prev = msg->flags;
            n -= syslog_partial;
            syslog_partial = 0;
        } else if (!len){
            /* partial read(), remember position */
            n = size;
            syslog_partial += n;
        } else
            n = 0;
        raw_spin_unlock_irq(&logbuf_lock);

        if (!n)
            break;

        if (copy_to_user(buf, text + skip, n)) {
            if (!len)
                len = -EFAULT;
            break;
        }

        len += n;
        size -= n;
        buf += n;
    }

    kfree(text);
    return len;
}

static int syslog_print_all(char __user *buf, int size, bool clear)
{
    char *text;
    int len = 0;

    text = kmalloc(LOG_LINE_MAX + PREFIX_MAX, GFP_KERNEL);
    if (!text)
        return -ENOMEM;

    raw_spin_lock_irq(&logbuf_lock);
    if (buf) {
        u64 next_seq;
        u64 seq;
        u32 idx;
        enum log_flags prev;

        if (clear_seq < log_first_seq) {
            /* messages are gone, move to first available one */
            clear_seq = log_first_seq;
            clear_idx = log_first_idx;
        }

        /*
         * Find first record that fits, including all following records,
         * into the user-provided buffer for this dump.
         */
        seq = clear_seq;
        idx = clear_idx;
        prev = 0;
        while (seq < log_next_seq) {
            struct log *msg = log_from_idx(idx);

            len += msg_print_text(msg, prev, true, NULL, 0);
            prev = msg->flags;
            idx = log_next(idx);
            seq++;
        }

        /* move first record forward until length fits into the buffer */
        seq = clear_seq;
        idx = clear_idx;
        prev = 0;
        while (len > size && seq < log_next_seq) {
            struct log *msg = log_from_idx(idx);

            len -= msg_print_text(msg, prev, true, NULL, 0);
            prev = msg->flags;
            idx = log_next(idx);
            seq++;
        }

        /* last message fitting into this dump */
        next_seq = log_next_seq;

        len = 0;
        prev = 0;
        while (len >= 0 && seq < next_seq) {
            struct log *msg = log_from_idx(idx);
            int textlen;

            textlen = msg_print_text(msg, prev, true, text,
                         LOG_LINE_MAX + PREFIX_MAX);
            if (textlen < 0) {
                len = textlen;
                break;
            }
            idx = log_next(idx);
            seq++;
            prev = msg->flags;

            raw_spin_unlock_irq(&logbuf_lock);
            if (copy_to_user(buf + len, text, textlen))
                len = -EFAULT;
            else
                len += textlen;
            raw_spin_lock_irq(&logbuf_lock);

            if (seq < log_first_seq) {
                /* messages are gone, move to next one */
                seq = log_first_seq;
                idx = log_first_idx;
                prev = 0;
            }
        }
    }

    if (clear) {
        clear_seq = log_next_seq;
        clear_idx = log_next_idx;
    }
    raw_spin_unlock_irq(&logbuf_lock);

    kfree(text);
    return len;
}

int do_syslog(int type, char __user *buf, int len, bool from_file)
{
    bool clear = false;
    static int saved_console_loglevel = -1;
    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,
                         syslog_seq != log_next_seq);
        if (error)
            goto out;
        error = syslog_print(buf, len);
        break;
    /* Read/clear last kernel messages */
    case SYSLOG_ACTION_READ_CLEAR:
        clear = true;
        /* 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;
        }
        error = syslog_print_all(buf, len, clear);
        break;
    /* Clear ring buffer */
    case SYSLOG_ACTION_CLEAR:
        syslog_print_all(NULL, 0, true);
        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:
        raw_spin_lock_irq(&logbuf_lock);
        if (syslog_seq < log_first_seq) {
            /* messages are gone, move to first one */
            syslog_seq = log_first_seq;
            syslog_idx = log_first_idx;
            syslog_prev = 0;
            syslog_partial = 0;
        }
        if (from_file) {
            /*
             * Short-cut for poll(/"proc/kmsg") which simply checks
             * for pending data, not the size; return the count of
             * records, not the length.
             */
            error = log_next_idx - syslog_idx;
        } else {
            u64 seq = syslog_seq;
            u32 idx = syslog_idx;
            enum log_flags prev = syslog_prev;

            error = 0;
            while (seq < log_next_seq) {
                struct log *msg = log_from_idx(idx);

                error += msg_print_text(msg, prev, true, NULL, 0);
                idx = log_next(idx);
                seq++;
                prev = msg->flags;
            }
            error -= syslog_partial;
        }
        raw_spin_unlock_irq(&logbuf_lock);
        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);
}

static bool __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);
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.");

/*
 * 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(int level, const char *text, size_t len)
{
    struct console *con;

    trace_console(text, 0, len, len);

    if (level >= console_loglevel && !ignore_loglevel)
        return;
    if (!console_drivers)
        return;

    for_each_console(con) {
        if (exclusive_console && con != exclusive_console)
            continue;
        if (!(con->flags & CON_ENABLED))
            continue;
        if (!con->write)
            continue;
        if (!cpu_online(smp_processor_id()) &&
            !(con->flags & CON_ANYTIME))
            continue;
        con->write(con, text, len);
    }
}

/*
 * 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);
}

/* 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;
}

/*
 * 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;
        }
    }
    logbuf_cpu = UINT_MAX;
    if (wake)
        up(&console_sem);
    raw_spin_unlock(&logbuf_lock);
    return retval;
}

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();
        }
    }
}

/*
 * Continuation lines are buffered, and not committed to the record buffer
 * until the line is complete, or a race forces it. The line fragments
 * though, are printed immediately to the consoles to ensure everything has
 * reached the console in case of a kernel crash.
 */
static struct cont {
    char buf[LOG_LINE_MAX];
    size_t len;         /* length == 0 means unused buffer */
    size_t cons;            /* bytes written to console */
    struct task_struct *owner;  /* task of first print*/
    u64 ts_nsec;            /* time of first print */
    u8 level;           /* log level of first message */
    u8 facility;            /* log level of first message */
    enum log_flags flags;       /* prefix, newline flags */
    bool flushed:1;         /* buffer sealed and committed */
} cont;

static void cont_flush(enum log_flags flags)
{
    if (cont.flushed)
        return;
    if (cont.len == 0)
        return;

    if (cont.cons) {
        /*
         * If a fragment of this line was directly flushed to the
         * console; wait for the console to pick up the rest of the
         * line. LOG_NOCONS suppresses a duplicated output.
         */
        log_store(cont.facility, cont.level, flags | LOG_NOCONS,
              cont.ts_nsec, NULL, 0, cont.buf, cont.len);
        cont.flags = flags;
        cont.flushed = true;
    } else {
        /*
         * If no fragment of this line ever reached the console,
         * just submit it to the store and free the buffer.
         */
        log_store(cont.facility, cont.level, flags, 0,
              NULL, 0, cont.buf, cont.len);
        cont.len = 0;
    }
}

static bool cont_add(int facility, int level, const char *text, size_t len)
{
    if (cont.len && cont.flushed)
        return false;

    if (cont.len + len > sizeof(cont.buf)) {
        /* the line gets too long, split it up in separate records */
        cont_flush(LOG_CONT);
        return false;
    }

    if (!cont.len) {
        cont.facility = facility;
        cont.level = level;
        cont.owner = current;
        cont.ts_nsec = local_clock();
        cont.flags = 0;
        cont.cons = 0;
        cont.flushed = false;
    }

    memcpy(cont.buf + cont.len, text, len);
    cont.len += len;

    if (cont.len > (sizeof(cont.buf) * 80) / 100)
        cont_flush(LOG_CONT);

    return true;
}

static size_t cont_print_text(char *text, size_t size)
{
    size_t textlen = 0;
    size_t len;

    if (cont.cons == 0 && (console_prev & LOG_NEWLINE)) {
        textlen += print_time(cont.ts_nsec, text);
        size -= textlen;
    }

    len = cont.len - cont.cons;
    if (len > 0) {
        if (len+1 > size)
            len = size-1;
        memcpy(text + textlen, cont.buf + cont.cons, len);
        textlen += len;
        cont.cons = cont.len;
    }

    if (cont.flushed) {
        if (cont.flags & LOG_NEWLINE)
            text[textlen++] = '\n';
        /* got everything, release buffer */
        cont.len = 0;
    }
    return textlen;
}

asmlinkage int vprintk_emit(int facility, int level,
                const char *dict, size_t dictlen,
                const char *fmt, va_list args)
{
    static int recursion_bug;
    static char textbuf[LOG_LINE_MAX];
    char *text = textbuf;
    size_t text_len;
    enum log_flags lflags = 0;
    unsigned long flags;
    int this_cpu;
    int printed_len = 0;

    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(logbuf_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);
    logbuf_cpu = this_cpu;

    if (recursion_bug) {
        static const char recursion_msg[] =
            "BUG: recent printk recursion!";

        recursion_bug = 0;
        printed_len += strlen(recursion_msg);
        /* emit KERN_CRIT message */
        log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
              NULL, 0, recursion_msg, printed_len);
    }

    /*
     * The printf needs to come first; we need the syslog
     * prefix which might be passed-in as a parameter.
     */
    text_len = vscnprintf(text, sizeof(textbuf), fmt, args);

    /* mark and strip a trailing newline */
    if (text_len && text[text_len-1] == '\n') {
        text_len--;
        lflags |= LOG_NEWLINE;
    }

    /* strip kernel syslog prefix and extract log level or control flags */
    if (facility == 0) {
        int kern_level = printk_get_level(text);

        if (kern_level) {
            const char *end_of_header = printk_skip_level(text);
            switch (kern_level) {
            case '0' ... '7':
                if (level == -1)
                    level = kern_level - '0';
            case 'd':   /* KERN_DEFAULT */
                lflags |= LOG_PREFIX;
            case 'c':   /* KERN_CONT */
                break;
            }
            text_len -= end_of_header - text;
            text = (char *)end_of_header;
        }
    }

    if (level == -1)
        level = default_message_loglevel;

    if (dict)
        lflags |= LOG_PREFIX|LOG_NEWLINE;

    if (!(lflags & LOG_NEWLINE)) {
        /*
         * Flush the conflicting buffer. An earlier newline was missing,
         * or another task also prints continuation lines.
         */
        if (cont.len && (lflags & LOG_PREFIX || cont.owner != current))
            cont_flush(LOG_NEWLINE);

        /* buffer line if possible, otherwise store it right away */
        if (!cont_add(facility, level, text, text_len))
            log_store(facility, level, lflags | LOG_CONT, 0,
                  dict, dictlen, text, text_len);
    } else {
        bool stored = false;

        /*
         * If an earlier newline was missing and it was the same task,
         * either merge it with the current buffer and flush, or if
         * there was a race with interrupts (prefix == true) then just
         * flush it out and store this line separately.
         */
        if (cont.len && cont.owner == current) {
            if (!(lflags & LOG_PREFIX))
                stored = cont_add(facility, level, text, text_len);
            cont_flush(LOG_NEWLINE);
        }

        if (!stored)
            log_store(facility, level, lflags, 0,
                  dict, dictlen, text, text_len);
    }
    printed_len += text_len;

    /*
     * Try to acquire and then immediately release the console semaphore.
     * The release will print out buffers and wake up /dev/kmsg and syslog()
     * users.
     *
     * The console_trylock_for_printk() function will release 'logbuf_lock'
     * regardless of whether it actually gets the console 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(vprintk_emit);

asmlinkage int vprintk(const char *fmt, va_list args)
{
    return vprintk_emit(0, -1, NULL, 0, fmt, args);
}
EXPORT_SYMBOL(vprintk);

asmlinkage int printk_emit(int facility, int level,
               const char *dict, size_t dictlen,
               const char *fmt, ...)
{
    va_list args;
    int r;

    va_start(args, fmt);
    r = vprintk_emit(facility, level, dict, dictlen, fmt, args);
    va_end(args);

    return r;
}
EXPORT_SYMBOL(printk_emit);

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_emit(0, -1, NULL, 0, fmt, args);
    va_end(args);

    return r;
}
EXPORT_SYMBOL(printk);

#else /* CONFIG_PRINTK */

#define LOG_LINE_MAX        0
#define PREFIX_MAX      0
#define LOG_LINE_MAX 0
static u64 syslog_seq;
static u32 syslog_idx;
static u64 console_seq;
static u32 console_idx;
static enum log_flags syslog_prev;
static u64 log_first_seq;
static u32 log_first_idx;
static u64 log_next_seq;
static enum log_flags console_prev;
static struct cont {
    size_t len;
    size_t cons;
    u8 level;
    bool flushed:1;
} cont;
static struct log *log_from_idx(u32 idx) { return NULL; }
static u32 log_next(u32 idx) { return 0; }
static void call_console_drivers(int level, const char *text, size_t len) {}
static size_t msg_print_text(const struct log *msg, enum log_flags prev,
                 bool syslog, char *buf, size_t size) { return 0; }
static size_t cont_print_text(char *text, size_t size) { return 0; }

#endif /* CONFIG_PRINTK */

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

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");

void suspend_console(void)
{
    if (!console_suspend_enabled)
        return;
    printk("Suspending console(s) (use no_console_suspend to debug)\n");
    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();
}

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_DOWN_FAILED:
    case CPU_UP_CANCELED:
        console_lock();
        console_unlock();
    }
    return NOTIFY_OK;
}

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);

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;
}

/*
 * Delayed printk version, for scheduler-internal messages:
 */
#define PRINTK_BUF_SIZE     512

#define PRINTK_PENDING_WAKEUP   0x01
#define PRINTK_PENDING_SCHED    0x02

static DEFINE_PER_CPU(int, printk_pending);
static DEFINE_PER_CPU(char [PRINTK_BUF_SIZE], printk_sched_buf);

void printk_tick(void)
{
    if (__this_cpu_read(printk_pending)) {
        int pending = __this_cpu_xchg(printk_pending, 0);
        if (pending & PRINTK_PENDING_SCHED) {
            char *buf = __get_cpu_var(printk_sched_buf);
            printk(KERN_WARNING "[sched_delayed] %s", buf);
        }
        if (pending & PRINTK_PENDING_WAKEUP)
            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_or(printk_pending, PRINTK_PENDING_WAKEUP);
}

static void console_cont_flush(char *text, size_t size)
{
    unsigned long flags;
    size_t len;

    raw_spin_lock_irqsave(&logbuf_lock, flags);

    if (!cont.len)
        goto out;

    /*
     * We still queue earlier records, likely because the console was
     * busy. The earlier ones need to be printed before this one, we
     * did not flush any fragment so far, so just let it queue up.
     */
    if (console_seq < log_next_seq && !cont.cons)
        goto out;

    len = cont_print_text(text, size);
    raw_spin_unlock(&logbuf_lock);
    stop_critical_timings();
    call_console_drivers(cont.level, text, len);
    start_critical_timings();
    local_irq_restore(flags);
    return;
out:
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);
}

void console_unlock(void)
{
    static char text[LOG_LINE_MAX + PREFIX_MAX];
    static u64 seen_seq;
    unsigned long flags;
    bool wake_klogd = false;
    bool retry;

    if (console_suspended) {
        up(&console_sem);
        return;
    }

    console_may_schedule = 0;

    /* flush buffered message fragment immediately to console */
    console_cont_flush(text, sizeof(text));
again:
    for (;;) {
        struct log *msg;
        size_t len;
        int level;

        raw_spin_lock_irqsave(&logbuf_lock, flags);
        if (seen_seq != log_next_seq) {
            wake_klogd = true;
            seen_seq = log_next_seq;
        }

        if (console_seq < log_first_seq) {
            /* messages are gone, move to first one */
            console_seq = log_first_seq;
            console_idx = log_first_idx;
            console_prev = 0;
        }
skip:
        if (console_seq == log_next_seq)
            break;

        msg = log_from_idx(console_idx);
        if (msg->flags & LOG_NOCONS) {
            /*
             * Skip record we have buffered and already printed
             * directly to the console when we received it.
             */
            console_idx = log_next(console_idx);
            console_seq++;
            /*
             * We will get here again when we register a new
             * CON_PRINTBUFFER console. Clear the flag so we
             * will properly dump everything later.
             */
            msg->flags &= ~LOG_NOCONS;
            console_prev = msg->flags;
            goto skip;
        }

        level = msg->level;
        len = msg_print_text(msg, console_prev, false,
                     text, sizeof(text));
        console_idx = log_next(console_idx);
        console_seq++;
        console_prev = msg->flags;
        raw_spin_unlock(&logbuf_lock);

        stop_critical_timings();    /* don't trace print latency */
        call_console_drivers(level, text, len);
        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);
    retry = console_seq != log_next_seq;
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);

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

    if (wake_klogd)
        wake_up_klogd();
}
EXPORT_SYMBOL(console_unlock);

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.\n");

    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\n",
                    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);
        console_seq = syslog_seq;
        console_idx = syslog_idx;
        console_prev = syslog_prev;
        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\n",
            newcon->name, newcon->index);
        for_each_console(bcon)
            if (bcon->flags & CON_BOOT)
                unregister_console(bcon);
    } else {
        printk(KERN_INFO "%sconsole [%s%d] enabled\n",
            (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\n",
                con->name, con->index);
            unregister_console(con);
        }
    }
    hotcpu_notifier(console_cpu_notify, 0);
    return 0;
}
late_initcall(printk_late_init);

#if defined CONFIG_PRINTK

int printk_sched(const char *fmt, ...)
{
    unsigned long flags;
    va_list args;
    char *buf;
    int r;

    local_irq_save(flags);
    buf = __get_cpu_var(printk_sched_buf);

    va_start(args, fmt);
    r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);
    va_end(args);

    __this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);
    local_irq_restore(flags);

    return r;
}

/*
 * 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);

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);

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);

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);

static bool always_kmsg_dump;
module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);

void kmsg_dump(enum kmsg_dump_reason reason)
{
    struct kmsg_dumper *dumper;
    unsigned long flags;

    if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
        return;

    rcu_read_lock();
    list_for_each_entry_rcu(dumper, &dump_list, list) {
        if (dumper->max_reason && reason > dumper->max_reason)
            continue;

        /* initialize iterator with data about the stored records */
        dumper->active = true;

        raw_spin_lock_irqsave(&logbuf_lock, flags);
        dumper->cur_seq = clear_seq;
        dumper->cur_idx = clear_idx;
        dumper->next_seq = log_next_seq;
        dumper->next_idx = log_next_idx;
        raw_spin_unlock_irqrestore(&logbuf_lock, flags);

        /* invoke dumper which will iterate over records */
        dumper->dump(dumper, reason);

        /* reset iterator */
        dumper->active = false;
    }
    rcu_read_unlock();
}

bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
                   char *line, size_t size, size_t *len)
{
    struct log *msg;
    size_t l = 0;
    bool ret = false;

    if (!dumper->active)
        goto out;

    if (dumper->cur_seq < log_first_seq) {
        /* messages are gone, move to first available one */
        dumper->cur_seq = log_first_seq;
        dumper->cur_idx = log_first_idx;
    }

    /* last entry */
    if (dumper->cur_seq >= log_next_seq)
        goto out;

    msg = log_from_idx(dumper->cur_idx);
    l = msg_print_text(msg, 0, syslog, line, size);

    dumper->cur_idx = log_next(dumper->cur_idx);
    dumper->cur_seq++;
    ret = true;
out:
    if (len)
        *len = l;
    return ret;
}

bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
            char *line, size_t size, size_t *len)
{
    unsigned long flags;
    bool ret;

    raw_spin_lock_irqsave(&logbuf_lock, flags);
    ret = kmsg_dump_get_line_nolock(dumper, syslog, line, size, len);
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);

    return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_line);

bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
              char *buf, size_t size, size_t *len)
{
    unsigned long flags;
    u64 seq;
    u32 idx;
    u64 next_seq;
    u32 next_idx;
    enum log_flags prev;
    size_t l = 0;
    bool ret = false;

    if (!dumper->active)
        goto out;

    raw_spin_lock_irqsave(&logbuf_lock, flags);
    if (dumper->cur_seq < log_first_seq) {
        /* messages are gone, move to first available one */
        dumper->cur_seq = log_first_seq;
        dumper->cur_idx = log_first_idx;
    }

    /* last entry */
    if (dumper->cur_seq >= dumper->next_seq) {
        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
        goto out;
    }

    /* calculate length of entire buffer */
    seq = dumper->cur_seq;
    idx = dumper->cur_idx;
    prev = 0;
    while (seq < dumper->next_seq) {
        struct log *msg = log_from_idx(idx);

        l += msg_print_text(msg, prev, true, NULL, 0);
        idx = log_next(idx);
        seq++;
        prev = msg->flags;
    }

    /* move first record forward until length fits into the buffer */
    seq = dumper->cur_seq;
    idx = dumper->cur_idx;
    prev = 0;
    while (l > size && seq < dumper->next_seq) {
        struct log *msg = log_from_idx(idx);

        l -= msg_print_text(msg, prev, true, NULL, 0);
        idx = log_next(idx);
        seq++;
        prev = msg->flags;
    }

    /* last message in next interation */
    next_seq = seq;
    next_idx = idx;

    l = 0;
    prev = 0;
    while (seq < dumper->next_seq) {
        struct log *msg = log_from_idx(idx);

        l += msg_print_text(msg, prev, syslog, buf + l, size - l);
        idx = log_next(idx);
        seq++;
        prev = msg->flags;
    }

    dumper->next_seq = next_seq;
    dumper->next_idx = next_idx;
    ret = true;
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);
out:
    if (len)
        *len = l;
    return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_buffer);

void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
{
    dumper->cur_seq = clear_seq;
    dumper->cur_idx = clear_idx;
    dumper->next_seq = log_next_seq;
    dumper->next_idx = log_next_idx;
}

void kmsg_dump_rewind(struct kmsg_dumper *dumper)
{
    unsigned long flags;

    raw_spin_lock_irqsave(&logbuf_lock, flags);
    kmsg_dump_rewind_nolock(dumper);
    raw_spin_unlock_irqrestore(&logbuf_lock, flags);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif