printk: use mutex lock to stop syslog_seq from going wild

[karo-tx-linux.git] / kernel / 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
 */

#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.
 */

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 */
        u16 level;              /* syslog level + facility */
};

/*
 * 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);

/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
static u32 syslog_idx;

/* 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;
#ifdef CONFIG_PRINTK
static u32 log_next_idx;

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

#define LOG_LINE_MAX 1024

/* 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,
                      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->level = (facility << 3) | (level & 7);
        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;
        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))
                        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;
        size_t len;
        ssize_t ret;

        if (!user)
                return -EBADF;

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

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

        msg = log_from_idx(user->idx);
        ts_usec = msg->ts_nsec;
        do_div(ts_usec, 1000);
        len = sprintf(user->buf, "%u,%llu,%llu;",
                      msg->level, user->seq, ts_usec);

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

                if (c < ' ' || c >= 128)
                        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 >= 128) {
                                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(&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(&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(&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(&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(&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(&logbuf_lock);
        user->idx = log_first_idx;
        user->seq = log_first_seq;
        raw_spin_unlock(&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);
}
#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_prefix(const struct log *msg, bool syslog, char *buf)
{
        size_t len = 0;

        if (syslog) {
                if (buf) {
                        len += sprintf(buf, "<%u>", msg->level);
                } else {
                        len += 3;
                        if (msg->level > 9)
                                len++;
                        if (msg->level > 99)
                                len++;
                }
        }

        if (printk_time) {
                if (buf) {
                        unsigned long long ts = msg->ts_nsec;
                        unsigned long rem_nsec = do_div(ts, 1000000000);

                        len += sprintf(buf + len, "[%5lu.%06lu] ",
                                         (unsigned long) ts, rem_nsec / 1000);
                } else {
                        len += 15;
                }
        }

        return len;
}

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

        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;

                        len += print_prefix(msg, syslog, buf + len);
                        memcpy(buf + len, text, text_len);
                        len += text_len;
                        buf[len++] = '\n';
                } else {
                        /* SYSLOG_ACTION_* buffer size only calculation */
                        len += print_prefix(msg, syslog, NULL);
                        len += text_len + 1;
                }

                text = next;
        } while (text);

        return len;
}

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

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

        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;
        }
        msg = log_from_idx(syslog_idx);
        len = msg_print_text(msg, true, text, LOG_LINE_MAX);
        syslog_idx = log_next(syslog_idx);
        syslog_seq++;
        raw_spin_unlock_irq(&logbuf_lock);

        if (len > 0 && copy_to_user(buf, text, len))
                len = -EFAULT;

        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, GFP_KERNEL);
        if (!text)
                return -ENOMEM;

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

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

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

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

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

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

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

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

                        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;
                        }
                }
        }

        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;
        static DEFINE_MUTEX(syslog_mutex);
        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 = mutex_lock_interruptible(&syslog_mutex);
                if (error)
                        goto out;
                error = wait_event_interruptible(log_wait,
                                                 syslog_seq != log_next_seq);
                if (error) {
                        mutex_unlock(&syslog_mutex);
                        goto out;
                }
                error = syslog_print(buf, len);
                mutex_unlock(&syslog_mutex);
                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);
        /* 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;
                }
                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;
                        u32 idx;

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

                                error += msg_print_text(msg, true, NULL, 0);
                                idx = log_next(idx);
                                seq++;
                        }
                }
                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);
}

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

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();
                }
        }
}

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 cont_buf[LOG_LINE_MAX];
        static size_t cont_len;
        static int cont_level;
        static struct task_struct *cont_task;
        static char textbuf[LOG_LINE_MAX];
        char *text = textbuf;
        size_t text_len;
        unsigned long flags;
        int this_cpu;
        bool newline = false;
        bool prefix = false;
        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, 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--;
                newline = true;
        }

        /* strip syslog prefix and extract log level or control flags */
        if (text[0] == '<' && text[1] && text[2] == '>') {
                switch (text[1]) {
                case '0' ... '7':
                        if (level == -1)
                                level = text[1] - '0';
                case 'd':       /* KERN_DEFAULT */
                        prefix = true;
                case 'c':       /* KERN_CONT */
                        text += 3;
                        text_len -= 3;
                }
        }

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

        if (dict) {
                prefix = true;
                newline = true;
        }

        if (!newline) {
                if (cont_len && (prefix || cont_task != current)) {
                        /*
                         * Flush earlier buffer, which is either from a
                         * different thread, or when we got a new prefix.
                         */
                        log_store(facility, cont_level, NULL, 0, cont_buf, cont_len);
                        cont_len = 0;
                }

                if (!cont_len) {
                        cont_level = level;
                        cont_task = current;
                }

                /* buffer or append to earlier buffer from the same thread */
                if (cont_len + text_len > sizeof(cont_buf))
                        text_len = sizeof(cont_buf) - cont_len;
                memcpy(cont_buf + cont_len, text, text_len);
                cont_len += text_len;
        } else {
                if (cont_len && cont_task == current) {
                        if (prefix) {
                                /*
                                 * New prefix from the same thread; flush. We
                                 * either got no earlier newline, or we race
                                 * with an interrupt.
                                 */
                                log_store(facility, cont_level,
                                          NULL, 0, cont_buf, cont_len);
                                cont_len = 0;
                        }

                        /* append to the earlier buffer and flush */
                        if (cont_len + text_len > sizeof(cont_buf))
                                text_len = sizeof(cont_buf) - cont_len;
                        memcpy(cont_buf + cont_len, text, text_len);
                        cont_len += text_len;
                        log_store(facility, cont_level,
                                  NULL, 0, cont_buf, cont_len);
                        cont_len = 0;
                        cont_task = NULL;
                        printed_len = cont_len;
                } else {
                        /* ordinary single and terminated line */
                        log_store(facility, level,
                                  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);

/**
 * printk - print a kernel message
 * @fmt: format string
 *
 * This is printk(). It can be called from any context. We want it to work.
 *
 * We try to grab the console_lock. If we succeed, it's easy - we log the
 * output and call the console drivers.  If we fail to get the semaphore, we
 * place the output into the log buffer and return. The current holder of
 * the console_sem will notice the new output in console_unlock(); and will
 * send it to the consoles before releasing the lock.
 *
 * One effect of this deferred printing is that code which calls printk() and
 * then changes console_loglevel may break. This is because console_loglevel
 * is inspected when the actual printing occurs.
 *
 * See also:
 * printf(3)
 *
 * See the vsnprintf() documentation for format string extensions over C99.
 */
asmlinkage int printk(const char *fmt, ...)
{
        va_list args;
        int r;

#ifdef CONFIG_KGDB_KDB
        if (unlikely(kdb_trap_printk)) {
                va_start(args, fmt);
                r = vkdb_printf(fmt, args);
                va_end(args);
                return r;
        }
#endif
        va_start(args, fmt);
        r = vprintk_emit(0, -1, NULL, 0, fmt, args);
        va_end(args);

        return r;
}
EXPORT_SYMBOL(printk);

#else

#define LOG_LINE_MAX 0
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, bool syslog,
                             char *buf, 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);

/**
 * add_preferred_console - add a device to the list of preferred consoles.
 * @name: device name
 * @idx: device index
 * @options: options for this console
 *
 * The last preferred console added will be used for kernel messages
 * and stdin/out/err for init.  Normally this is used by console_setup
 * above to handle user-supplied console arguments; however it can also
 * be used by arch-specific code either to override the user or more
 * commonly to provide a default console (ie from PROM variables) when
 * the user has not supplied one.
 */
int add_preferred_console(char *name, int idx, char *options)
{
        return __add_preferred_console(name, idx, options, NULL);
}

int update_console_cmdline(char *name, int idx, char *name_new, int idx_new, char *options)
{
        struct console_cmdline *c;
        int i;

        for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0]; i++)
                if (strcmp(console_cmdline[i].name, name) == 0 &&
                          console_cmdline[i].index == idx) {
                                c = &console_cmdline[i];
                                strlcpy(c->name, name_new, sizeof(c->name));
                                c->name[sizeof(c->name) - 1] = 0;
                                c->options = options;
                                c->index = idx_new;
                                return i;
                }
        /* not found */
        return -1;
}

bool console_suspend_enabled = 1;
EXPORT_SYMBOL(console_suspend_enabled);

static int __init console_suspend_disable(char *str)
{
        console_suspend_enabled = 0;
        return 1;
}
__setup("no_console_suspend", console_suspend_disable);
module_param_named(console_suspend, console_suspend_enabled,
                bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(console_suspend, "suspend console during suspend"
        " and hibernate operations");

/**
 * suspend_console - suspend the console subsystem
 *
 * This disables printk() while we go into suspend states
 */
void suspend_console(void)
{
        if (!console_suspend_enabled)
                return;
        printk("Suspending console(s) (use no_console_suspend to debug)\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();
}

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

/**
 * console_lock - lock the console system for exclusive use.
 *
 * Acquires a lock which guarantees that the caller has
 * exclusive access to the console system and the console_drivers list.
 *
 * Can sleep, returns nothing.
 */
void console_lock(void)
{
        BUG_ON(in_interrupt());
        down(&console_sem);
        if (console_suspended)
                return;
        console_locked = 1;
        console_may_schedule = 1;
}
EXPORT_SYMBOL(console_lock);

/**
 * console_trylock - try to lock the console system for exclusive use.
 *
 * Tried to acquire a lock which guarantees that the caller has
 * exclusive access to the console system and the console_drivers list.
 *
 * returns 1 on success, and 0 on failure to acquire the lock.
 */
int console_trylock(void)
{
        if (down_trylock(&console_sem))
                return 0;
        if (console_suspended) {
                up(&console_sem);
                return 0;
        }
        console_locked = 1;
        console_may_schedule = 0;
        return 1;
}
EXPORT_SYMBOL(console_trylock);

int is_console_locked(void)
{
        return console_locked;
}

/*
 * 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);
}

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

/**
 * console_unlock - unlock the console system
 *
 * Releases the console_lock which the caller holds on the console system
 * and the console driver list.
 *
 * While the console_lock was held, console output may have been buffered
 * by printk().  If this is the case, console_unlock(); emits
 * the output prior to releasing the lock.
 *
 * If there is output waiting, we wake /dev/kmsg and syslog() users.
 *
 * console_unlock(); may be called from any context.
 */
void console_unlock(void)
{
        static u64 seen_seq;
        unsigned long flags;
        bool wake_klogd = false;
        bool retry;

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

        console_may_schedule = 0;

again:
        for (;;) {
                struct log *msg;
                static char text[LOG_LINE_MAX];
                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;
                }

                if (console_seq == log_next_seq)
                        break;

                msg = log_from_idx(console_idx);
                level = msg->level & 7;

                len = msg_print_text(msg, false, text, sizeof(text));

                console_idx = log_next(console_idx);
                console_seq++;
                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);

/**
 * console_conditional_schedule - yield the CPU if required
 *
 * If the console code is currently allowed to sleep, and
 * if this CPU should yield the CPU to another task, do
 * so here.
 *
 * Must be called within console_lock();.
 */
void __sched console_conditional_schedule(void)
{
        if (console_may_schedule)
                cond_resched();
}
EXPORT_SYMBOL(console_conditional_schedule);

void console_unblank(void)
{
        struct console *c;

        /*
         * console_unblank can no longer be called in interrupt context unless
         * oops_in_progress is set to 1..
         */
        if (oops_in_progress) {
                if (down_trylock(&console_sem) != 0)
                        return;
        } else
                console_lock();

        console_locked = 1;
        console_may_schedule = 0;
        for_each_console(c)
                if ((c->flags & CON_ENABLED) && c->unblank)
                        c->unblank();
        console_unlock();
}

/*
 * Return the console tty driver structure and its associated index
 */
struct tty_driver *console_device(int *index)
{
        struct console *c;
        struct tty_driver *driver = NULL;

        console_lock();
        for_each_console(c) {
                if (!c->device)
                        continue;
                driver = c->device(c, index);
                if (driver)
                        break;
        }
        console_unlock();
        return driver;
}

/*
 * Prevent further output on the passed console device so that (for example)
 * serial drivers can disable console output before suspending a port, and can
 * re-enable output afterwards.
 */
void console_stop(struct console *console)
{
        console_lock();
        console->flags &= ~CON_ENABLED;
        console_unlock();
}
EXPORT_SYMBOL(console_stop);

void console_start(struct console *console)
{
        console_lock();
        console->flags |= CON_ENABLED;
        console_unlock();
}
EXPORT_SYMBOL(console_start);

static int __read_mostly keep_bootcon;

static int __init keep_bootcon_setup(char *str)
{
        keep_bootcon = 1;
        printk(KERN_INFO "debug: skip boot console de-registration.\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;
                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);

/**
 * printk_timed_ratelimit - caller-controlled printk ratelimiting
 * @caller_jiffies: pointer to caller's state
 * @interval_msecs: minimum interval between prints
 *
 * printk_timed_ratelimit() returns true if more than @interval_msecs
 * milliseconds have elapsed since the last time printk_timed_ratelimit()
 * returned true.
 */
bool printk_timed_ratelimit(unsigned long *caller_jiffies,
                        unsigned int interval_msecs)
{
        if (*caller_jiffies == 0
                        || !time_in_range(jiffies, *caller_jiffies,
                                        *caller_jiffies
                                        + msecs_to_jiffies(interval_msecs))) {
                *caller_jiffies = jiffies;
                return true;
        }
        return false;
}
EXPORT_SYMBOL(printk_timed_ratelimit);

static DEFINE_SPINLOCK(dump_list_lock);
static LIST_HEAD(dump_list);

/**
 * kmsg_dump_register - register a kernel log dumper.
 * @dumper: pointer to the kmsg_dumper structure
 *
 * Adds a kernel log dumper to the system. The dump callback in the
 * structure will be called when the kernel oopses or panics and must be
 * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
 */
int kmsg_dump_register(struct kmsg_dumper *dumper)
{
        unsigned long flags;
        int err = -EBUSY;

        /* The dump callback needs to be set */
        if (!dumper->dump)
                return -EINVAL;

        spin_lock_irqsave(&dump_list_lock, flags);
        /* Don't allow registering multiple times */
        if (!dumper->registered) {
                dumper->registered = 1;
                list_add_tail_rcu(&dumper->list, &dump_list);
                err = 0;
        }
        spin_unlock_irqrestore(&dump_list_lock, flags);

        return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_register);

/**
 * kmsg_dump_unregister - unregister a kmsg dumper.
 * @dumper: pointer to the kmsg_dumper structure
 *
 * Removes a dump device from the system. Returns zero on success and
 * %-EINVAL otherwise.
 */
int kmsg_dump_unregister(struct kmsg_dumper *dumper)
{
        unsigned long flags;
        int err = -EINVAL;

        spin_lock_irqsave(&dump_list_lock, flags);
        if (dumper->registered) {
                dumper->registered = 0;
                list_del_rcu(&dumper->list);
                err = 0;
        }
        spin_unlock_irqrestore(&dump_list_lock, flags);
        synchronize_rcu();

        return err;
}
EXPORT_SYMBOL_GPL(kmsg_dump_unregister);

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

/**
 * kmsg_dump - dump kernel log to kernel message dumpers.
 * @reason: the reason (oops, panic etc) for dumping
 *
 * Call each of the registered dumper's dump() callback, which can
 * retrieve the kmsg records with kmsg_dump_get_line() or
 * kmsg_dump_get_buffer().
 */
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();
}

/**
 * kmsg_dump_get_line - retrieve one kmsg log line
 * @dumper: registered kmsg dumper
 * @syslog: include the "<4>" prefixes
 * @line: buffer to copy the line to
 * @size: maximum size of the buffer
 * @len: length of line placed into buffer
 *
 * Start at the beginning of the kmsg buffer, with the oldest kmsg
 * record, and copy one record into the provided buffer.
 *
 * Consecutive calls will return the next available record moving
 * towards the end of the buffer with the youngest messages.
 *
 * A return value of FALSE indicates that there are no more records to
 * read.
 */
bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
                        char *line, size_t size, size_t *len)
{
        unsigned long flags;
        struct log *msg;
        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 >= log_next_seq) {
                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
                goto out;
        }

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

        dumper->cur_idx = log_next(dumper->cur_idx);
        dumper->cur_seq++;
        ret = true;
        raw_spin_unlock_irqrestore(&logbuf_lock, flags);
out:
        if (len)
                *len = l;
        return ret;
}
EXPORT_SYMBOL_GPL(kmsg_dump_get_line);

/**
 * kmsg_dump_get_buffer - copy kmsg log lines
 * @dumper: registered kmsg dumper
 * @syslog: include the "<4>" prefixes
 * @line: buffer to copy the line to
 * @size: maximum size of the buffer
 * @len: length of line placed into buffer
 *
 * Start at the end of the kmsg buffer and fill the provided buffer
 * with as many of the the *youngest* kmsg records that fit into it.
 * If the buffer is large enough, all available kmsg records will be
 * copied with a single call.
 *
 * Consecutive calls will fill the buffer with the next block of
 * available older records, not including the earlier retrieved ones.
 *
 * A return value of FALSE indicates that there are no more records to
 * read.
 */
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;
        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;
        while (seq < dumper->next_seq) {
                struct log *msg = log_from_idx(idx);

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

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

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

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

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

                l += msg_print_text(msg, syslog,
                                    buf + l, size - l);

                idx = log_next(idx);
                seq++;
        }

        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);

/**
 * kmsg_dump_rewind - reset the interator
 * @dumper: registered kmsg dumper
 *
 * Reset the dumper's iterator so that kmsg_dump_get_line() and
 * kmsg_dump_get_buffer() can be called again and used multiple
 * times within the same dumper.dump() callback.
 */
void kmsg_dump_rewind(struct kmsg_dumper *dumper)
{
        unsigned long flags;

        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);
}
EXPORT_SYMBOL_GPL(kmsg_dump_rewind);
#endif