1 files changed, 1331 insertions, 437 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index b663c2c95d39..177fa49357a5 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -41,6 +41,7 @@
 #include <linux/cpu.h>
 #include <linux/notifier.h>
 #include <linux/rculist.h>
+#include <linux/poll.h>
 
 #include <asm/uaccess.h>
 
@@ -54,8 +55,6 @@ void asmlinkage __attribute__((weak)) early_printk(const char *fmt, ...)
 {
 }
 
-#define __LOG_BUF_LEN   (1 << CONFIG_LOG_BUF_SHIFT)
-
 /* printk's without a loglevel use this.. */
 #define DEFAULT_MESSAGE_LOGLEVEL CONFIG_DEFAULT_MESSAGE_LOGLEVEL
 
@@ -99,24 +98,6 @@ EXPORT_SYMBOL_GPL(console_drivers);
 static int console_locked, console_suspended;
 
 /*
- * logbuf_lock protects log_buf, log_start, log_end, con_start and logged_chars
- * It is also used in interesting ways to provide interlocking in
- * console_unlock();.
- */
-static DEFINE_RAW_SPINLOCK(logbuf_lock);
-
-#define LOG_BUF_MASK (log_buf_len-1)
-#define LOG_BUF(idx) (log_buf[(idx) & LOG_BUF_MASK])
-
-/*
- * The indices into log_buf are not constrained to log_buf_len - they
- * must be masked before subscripting
- */
-static unsigned log_start;      /* Index into log_buf: next char to be read by syslog() */
-static unsigned con_start;      /* Index into log_buf: next char to be sent to consoles */
-static unsigned log_end;        /* Index into log_buf: most-recently-written-char + 1 */
-
-/*
  * If exclusive_console is non-NULL then only this console is to be printed to.
  */
 static struct console *exclusive_console;
@@ -145,13 +126,510 @@ 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);
+
+/* 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;
 #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;
 
-static char __log_buf[__LOG_BUF_LEN];
+#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 int log_buf_len = __LOG_BUF_LEN;
-static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
-static int saved_console_loglevel = -1;
+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;
+        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_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);
+        len = sprintf(user->buf, "%u,%llu,%llu;",
+                      (msg->facility << 3) | 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 >= 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
 /*
@@ -165,9 +643,9 @@ static int saved_console_loglevel = -1;
 void log_buf_kexec_setup(void)
 {
         VMCOREINFO_SYMBOL(log_buf);
-        VMCOREINFO_SYMBOL(log_end);
         VMCOREINFO_SYMBOL(log_buf_len);
-        VMCOREINFO_SYMBOL(logged_chars);
+        VMCOREINFO_SYMBOL(log_first_idx);
+        VMCOREINFO_SYMBOL(log_next_idx);
 }
 #endif
 
@@ -191,7 +669,6 @@ early_param("log_buf_len", log_buf_len_setup);
 void __init setup_log_buf(int early)
 {
         unsigned long flags;
-        unsigned start, dest_idx, offset;
         char *new_log_buf;
         int free;
 
@@ -219,20 +696,8 @@ void __init setup_log_buf(int early)
         log_buf_len = new_log_buf_len;
         log_buf = new_log_buf;
         new_log_buf_len = 0;
-        free = __LOG_BUF_LEN - log_end;
-
-        offset = start = min(con_start, log_start);
-        dest_idx = 0;
-        while (start != log_end) {
-                unsigned log_idx_mask = start & (__LOG_BUF_LEN - 1);
-
-                log_buf[dest_idx] = __log_buf[log_idx_mask];
-                start++;
-                dest_idx++;
-        }
-        log_start -= offset;
-        con_start -= offset;
-        log_end -= offset;
+        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);
@@ -332,11 +797,270 @@ static int check_syslog_permissions(int type, bool from_file)
         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, 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);
+                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, 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);
+                        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);
+                        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);
+                        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)
 {
-        unsigned i, j, limit, count;
-        int do_clear = 0;
-        char c;
+        bool clear = false;
+        static int saved_console_loglevel = -1;
         int error;
 
         error = check_syslog_permissions(type, from_file);
@@ -364,28 +1088,14 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                         goto out;
                 }
                 error = wait_event_interruptible(log_wait,
-                                                        (log_start - log_end));
+                                                 syslog_seq != log_next_seq);
                 if (error)
                         goto out;
-                i = 0;
-                raw_spin_lock_irq(&logbuf_lock);
-                while (!error && (log_start != log_end) && i < len) {
-                        c = LOG_BUF(log_start);
-                        log_start++;
-                        raw_spin_unlock_irq(&logbuf_lock);
-                        error = __put_user(c,buf);
-                        buf++;
-                        i++;
-                        cond_resched();
-                        raw_spin_lock_irq(&logbuf_lock);
-                }
-                raw_spin_unlock_irq(&logbuf_lock);
-                if (!error)
-                        error = i;
+                error = syslog_print(buf, len);
                 break;
         /* Read/clear last kernel messages */
         case SYSLOG_ACTION_READ_CLEAR:
-                do_clear = 1;
+                clear = true;
                 /* FALL THRU */
         /* Read last kernel messages */
         case SYSLOG_ACTION_READ_ALL:
@@ -399,51 +1109,11 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                         error = -EFAULT;
                         goto out;
                 }
-                count = len;
-                if (count > log_buf_len)
-                        count = log_buf_len;
-                raw_spin_lock_irq(&logbuf_lock);
-                if (count > logged_chars)
-                        count = logged_chars;
-                if (do_clear)
-                        logged_chars = 0;
-                limit = log_end;
-                /*
-                 * __put_user() could sleep, and while we sleep
-                 * printk() could overwrite the messages
-                 * we try to copy to user space. Therefore
-                 * the messages are copied in reverse. <manfreds>
-                 */
-                for (i = 0; i < count && !error; i++) {
-                        j = limit-1-i;
-                        if (j + log_buf_len < log_end)
-                                break;
-                        c = LOG_BUF(j);
-                        raw_spin_unlock_irq(&logbuf_lock);
-                        error = __put_user(c,&buf[count-1-i]);
-                        cond_resched();
-                        raw_spin_lock_irq(&logbuf_lock);
-                }
-                raw_spin_unlock_irq(&logbuf_lock);
-                if (error)
-                        break;
-                error = i;
-                if (i != count) {
-                        int offset = count-error;
-                        /* buffer overflow during copy, correct user buffer. */
-                        for (i = 0; i < error; i++) {
-                                if (__get_user(c,&buf[i+offset]) ||
-                                    __put_user(c,&buf[i])) {
-                                        error = -EFAULT;
-                                        break;
-                                }
-                                cond_resched();
-                        }
-                }
+                error = syslog_print_all(buf, len, clear);
                 break;
         /* Clear ring buffer */
         case SYSLOG_ACTION_CLEAR:
-                logged_chars = 0;
+                syslog_print_all(NULL, 0, true);
                 break;
         /* Disable logging to console */
         case SYSLOG_ACTION_CONSOLE_OFF:
@@ -472,7 +1142,38 @@ int do_syslog(int type, char __user *buf, int len, bool from_file)
                 break;
         /* Number of chars in the log buffer */
         case SYSLOG_ACTION_SIZE_UNREAD:
-                error = log_end - log_start;
+                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:
@@ -501,29 +1202,11 @@ 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_end -
-                (logged_chars < log_buf_len ? logged_chars : log_buf_len);
-        syslog_data[3] = log_buf + log_end;
+        syslog_data[2] = log_buf + log_first_idx;
+        syslog_data[3] = log_buf + log_next_idx;
 }
 #endif  /* CONFIG_KGDB_KDB */
 
-/*
- * Call the console drivers on a range of log_buf
- */
-static void __call_console_drivers(unsigned start, unsigned end)
-{
-        struct console *con;
-
-        for_each_console(con) {
-                if (exclusive_console && con != exclusive_console)
-                        continue;
-                if ((con->flags & CON_ENABLED) && con->write &&
-                                (cpu_online(smp_processor_id()) ||
-                                (con->flags & CON_ANYTIME)))
-                        con->write(con, &LOG_BUF(start), end - start);
-        }
-}
-
 static bool __read_mostly ignore_loglevel;
 
 static int __init ignore_loglevel_setup(char *str)
@@ -540,142 +1223,33 @@ MODULE_PARM_DESC(ignore_loglevel, "ignore loglevel setting, to"
         "print all kernel messages to the console.");
 
 /*
- * Write out chars from start to end - 1 inclusive
- */
-static void _call_console_drivers(unsigned start,
-                                unsigned end, int msg_log_level)
-{
-        trace_console(&LOG_BUF(0), start, end, log_buf_len);
-
-        if ((msg_log_level < console_loglevel || ignore_loglevel) &&
-                        console_drivers && start != end) {
-                if ((start & LOG_BUF_MASK) > (end & LOG_BUF_MASK)) {
-                        /* wrapped write */
-                        __call_console_drivers(start & LOG_BUF_MASK,
-                                                log_buf_len);
-                        __call_console_drivers(0, end & LOG_BUF_MASK);
-                } else {
-                        __call_console_drivers(start, end);
-                }
-        }
-}
-
-/*
- * Parse the syslog header <[0-9]*>. The decimal value represents 32bit, the
- * lower 3 bit are the log level, the rest are the log facility. In case
- * userspace passes usual userspace syslog messages to /dev/kmsg or
- * /dev/ttyprintk, the log prefix might contain the facility. Printk needs
- * to extract the correct log level for in-kernel processing, and not mangle
- * the original value.
- *
- * If a prefix is found, the length of the prefix is returned. If 'level' is
- * passed, it will be filled in with the log level without a possible facility
- * value. If 'special' is passed, the special printk prefix chars are accepted
- * and returned. If no valid header is found, 0 is returned and the passed
- * variables are not touched.
- */
-static size_t log_prefix(const char *p, unsigned int *level, char *special)
-{
-        unsigned int lev = 0;
-        char sp = '\0';
-        size_t len;
-
-        if (p[0] != '<' || !p[1])
-                return 0;
-        if (p[2] == '>') {
-                /* usual single digit level number or special char */
-                switch (p[1]) {
-                case '0' ... '7':
-                        lev = p[1] - '0';
-                        break;
-                case 'c': /* KERN_CONT */
-                case 'd': /* KERN_DEFAULT */
-                        sp = p[1];
-                        break;
-                default:
-                        return 0;
-                }
-                len = 3;
-        } else {
-                /* multi digit including the level and facility number */
-                char *endp = NULL;
-
-                lev = (simple_strtoul(&p[1], &endp, 10) & 7);
-                if (endp == NULL || endp[0] != '>')
-                        return 0;
-                len = (endp + 1) - p;
-        }
-
-        /* do not accept special char if not asked for */
-        if (sp && !special)
-                return 0;
-
-        if (special) {
-                *special = sp;
-                /* return special char, do not touch level */
-                if (sp)
-                        return len;
-        }
-
-        if (level)
-                *level = lev;
-        return len;
-}
-
-/*
  * 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(unsigned start, unsigned end)
+static void call_console_drivers(int level, const char *text, size_t len)
 {
-        unsigned cur_index, start_print;
-        static int msg_level = -1;
+        struct console *con;
 
-        BUG_ON(((int)(start - end)) > 0);
+        trace_console(text, 0, len, len);
 
-        cur_index = start;
-        start_print = start;
-        while (cur_index != end) {
-                if (msg_level < 0 && ((end - cur_index) > 2)) {
-                        /* strip log prefix */
-                        cur_index += log_prefix(&LOG_BUF(cur_index), &msg_level, NULL);
-                        start_print = cur_index;
-                }
-                while (cur_index != end) {
-                        char c = LOG_BUF(cur_index);
-
-                        cur_index++;
-                        if (c == '\n') {
-                                if (msg_level < 0) {
-                                        /*
-                                         * printk() has already given us loglevel tags in
-                                         * the buffer.  This code is here in case the
-                                         * log buffer has wrapped right round and scribbled
-                                         * on those tags
-                                         */
-                                        msg_level = default_message_loglevel;
-                                }
-                                _call_console_drivers(start_print, cur_index, msg_level);
-                                msg_level = -1;
-                                start_print = cur_index;
-                                break;
-                        }
-                }
-        }
-        _call_console_drivers(start_print, end, msg_level);
-}
+        if (level >= console_loglevel && !ignore_loglevel)
+                return;
+        if (!console_drivers)
+                return;
 
-static void emit_log_char(char c)
-{
-        LOG_BUF(log_end) = c;
-        log_end++;
-        if (log_end - log_start > log_buf_len)
-                log_start = log_end - log_buf_len;
-        if (log_end - con_start > log_buf_len)
-                con_start = log_end - log_buf_len;
-        if (logged_chars < log_buf_len)
-                logged_chars++;
+        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);
+        }
 }
 
 /*
@@ -700,16 +1274,6 @@ static void zap_locks(void)
         sema_init(&console_sem, 1);
 }
 
-#if defined(CONFIG_PRINTK_TIME)
-static bool printk_time = 1;
-#else
-static bool printk_time = 0;
-#endif
-module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);
-
-static bool always_kmsg_dump;
-module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
-
 /* Check if we have any console registered that can be called early in boot. */
 static int have_callable_console(void)
 {
@@ -722,51 +1286,6 @@ static int have_callable_console(void)
         return 0;
 }
 
-/**
- * printk - print a kernel message
- * @fmt: format string
- *
- * This is printk().  It can be called from any context.  We want it to work.
- *
- * 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(fmt, args);
-        va_end(args);
-
-        return r;
-}
-
-/* cpu currently holding logbuf_lock */
-static volatile unsigned int printk_cpu = UINT_MAX;
-
 /*
  * Can we actually use the console at this time on this cpu?
  *
@@ -810,17 +1329,12 @@ static int console_trylock_for_printk(unsigned int cpu)
                         retval = 0;
                 }
         }
-        printk_cpu = UINT_MAX;
+        logbuf_cpu = UINT_MAX;
         if (wake)
                 up(&console_sem);
         raw_spin_unlock(&logbuf_lock);
         return retval;
 }
-static const char recursion_bug_msg [] =
-                KERN_CRIT "BUG: recent printk recursion!\n";
-static int recursion_bug;
-static int new_text_line = 1;
-static char printk_buf[1024];
 
 int printk_delay_msec __read_mostly;
 
@@ -836,15 +1350,99 @@ static inline void printk_delay(void)
         }
 }
 
-asmlinkage int vprintk(const char *fmt, va_list args)
+/*
+ * 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 */
+        bool flushed:1;                 /* buffer sealed and committed */
+} cont;
+
+static void cont_flush(void)
 {
-        int printed_len = 0;
-        int current_log_level = default_message_loglevel;
+        if (cont.flushed)
+                return;
+        if (cont.len == 0)
+                return;
+
+        log_store(cont.facility, cont.level, LOG_NOCONS, cont.ts_nsec,
+                  NULL, 0, cont.buf, cont.len);
+
+        cont.flushed = true;
+}
+
+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)) {
+                cont_flush();
+                return false;
+        }
+
+        if (!cont.len) {
+                cont.facility = facility;
+                cont.level = level;
+                cont.owner = current;
+                cont.ts_nsec = local_clock();
+                cont.cons = 0;
+                cont.flushed = false;
+        }
+
+        memcpy(cont.buf + cont.len, text, len);
+        cont.len += len;
+        return true;
+}
+
+static size_t cont_print_text(char *text, size_t size)
+{
+        size_t textlen = 0;
+        size_t len;
+
+        if (cont.cons == 0) {
+                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) {
+                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;
-        char *p;
-        size_t plen;
-        char special;
+        int printed_len = 0;
 
         boot_delay_msec();
         printk_delay();
@@ -856,7 +1454,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
         /*
          * Ouch, printk recursed into itself!
          */
-        if (unlikely(printk_cpu == this_cpu)) {
+        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
@@ -873,97 +1471,91 @@ asmlinkage int vprintk(const char *fmt, va_list args)
 
         lockdep_off();
         raw_spin_lock(&logbuf_lock);
-        printk_cpu = this_cpu;
+        logbuf_cpu = this_cpu;
 
         if (recursion_bug) {
+                static const char recursion_msg[] =
+                        "BUG: recent printk recursion!";
+
                 recursion_bug = 0;
-                strcpy(printk_buf, recursion_bug_msg);
-                printed_len = strlen(recursion_bug_msg);
+                printed_len += strlen(recursion_msg);
+                /* emit KERN_CRIT message */
+                log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
+                          NULL, 0, recursion_msg, printed_len);
         }
-        /* Emit the output into the temporary buffer */
-        printed_len += vscnprintf(printk_buf + printed_len,
-                                  sizeof(printk_buf) - printed_len, fmt, args);
 
-        p = printk_buf;
+        /*
+         * 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);
 
-        /* Read log level and handle special printk prefix */
-        plen = log_prefix(p, &current_log_level, &special);
-        if (plen) {
-                p += plen;
+        /* mark and strip a trailing newline */
+        if (text_len && text[text_len-1] == '\n') {
+                text_len--;
+                lflags |= LOG_NEWLINE;
+        }
 
-                switch (special) {
-                case 'c': /* Strip <c> KERN_CONT, continue line */
-                        plen = 0;
-                        break;
-                case 'd': /* Strip <d> KERN_DEFAULT, start new line */
-                        plen = 0;
-                default:
-                        if (!new_text_line) {
-                                emit_log_char('\n');
-                                new_text_line = 1;
-                        }
+        /* 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 */
+                        lflags |= LOG_PREFIX;
+                case 'c':       /* KERN_CONT */
+                        text += 3;
+                        text_len -= 3;
                 }
         }
 
-        /*
-         * Copy the output into log_buf. If the caller didn't provide
-         * the appropriate log prefix, we insert them here
-         */
-        for (; *p; p++) {
-                if (new_text_line) {
-                        new_text_line = 0;
-
-                        if (plen) {
-                                /* Copy original log prefix */
-                                int i;
-
-                                for (i = 0; i < plen; i++)
-                                        emit_log_char(printk_buf[i]);
-                                printed_len += plen;
-                        } else {
-                                /* Add log prefix */
-                                emit_log_char('<');
-                                emit_log_char(current_log_level + '0');
-                                emit_log_char('>');
-                                printed_len += 3;
-                        }
+        if (level == -1)
+                level = default_message_loglevel;
 
-                        if (printk_time) {
-                                /* Add the current time stamp */
-                                char tbuf[50], *tp;
-                                unsigned tlen;
-                                unsigned long long t;
-                                unsigned long nanosec_rem;
-
-                                t = cpu_clock(printk_cpu);
-                                nanosec_rem = do_div(t, 1000000000);
-                                tlen = sprintf(tbuf, "[%5lu.%06lu] ",
-                                                (unsigned long) t,
-                                                nanosec_rem / 1000);
-
-                                for (tp = tbuf; tp < tbuf + tlen; tp++)
-                                        emit_log_char(*tp);
-                                printed_len += tlen;
-                        }
+        if (dict)
+                lflags |= LOG_PREFIX|LOG_NEWLINE;
 
-                        if (!*p)
-                                break;
+        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();
+
+                /* 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();
                 }
 
-                emit_log_char(*p);
-                if (*p == '\n')
-                        new_text_line = 1;
+                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 do all the
-         * actual magic (print out buffers, wake up klogd,
-         * etc). 
+         * 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 semaphore or not.
+         * 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();
@@ -974,16 +1566,88 @@ out_restore_irqs:
 
         return printed_len;
 }
-EXPORT_SYMBOL(printk);
-EXPORT_SYMBOL(vprintk);
+EXPORT_SYMBOL(vprintk_emit);
 
-#else
+asmlinkage int vprintk(const char *fmt, va_list args)
+{
+        return vprintk_emit(0, -1, NULL, 0, fmt, args);
+}
+EXPORT_SYMBOL(vprintk);
 
-static void call_console_drivers(unsigned start, unsigned end)
+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 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)
@@ -1217,7 +1881,7 @@ int is_console_locked(void)
 }
 
 /*
- * Delayed printk facility, for scheduler-internal messages:
+ * Delayed printk version, for scheduler-internal messages:
  */
 #define PRINTK_BUF_SIZE         512
 
@@ -1253,6 +1917,11 @@ void wake_up_klogd(void)
                 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;
+static enum log_flags console_prev;
+
 /**
  * console_unlock - unlock the console system
  *
@@ -1263,15 +1932,17 @@ void wake_up_klogd(void)
  * by printk().  If this is the case, console_unlock(); emits
  * the output prior to releasing the lock.
  *
- * If there is output waiting for klogd, we wake it up.
+ * 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 char text[LOG_LINE_MAX];
+        static u64 seen_seq;
         unsigned long flags;
-        unsigned _con_start, _log_end;
-        unsigned wake_klogd = 0, retry = 0;
+        bool wake_klogd = false;
+        bool retry;
 
         if (console_suspended) {
                 up(&console_sem);
@@ -1280,18 +1951,69 @@ void console_unlock(void)
 
         console_may_schedule = 0;
 
+        /* flush buffered message fragment immediately to console */
+        raw_spin_lock_irqsave(&logbuf_lock, flags);
+        if (cont.len && (cont.cons < cont.len || cont.flushed)) {
+                size_t len;
+
+                len = cont_print_text(text, sizeof(text));
+                raw_spin_unlock(&logbuf_lock);
+                stop_critical_timings();
+                call_console_drivers(cont.level, text, len);
+                start_critical_timings();
+                local_irq_restore(flags);
+        } else
+                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+
 again:
-        for ( ; ; ) {
+        for (;;) {
+                struct log *msg;
+                size_t len;
+                int level;
+
                 raw_spin_lock_irqsave(&logbuf_lock, flags);
-                wake_klogd |= log_start - log_end;
-                if (con_start == log_end)
-                        break;                  /* Nothing to print */
-                _con_start = con_start;
-                _log_end = log_end;
-                con_start = log_end;            /* Flush */
+                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;
+                        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(_con_start, _log_end);
+                call_console_drivers(level, text, len);
                 start_critical_timings();
                 local_irq_restore(flags);
         }
@@ -1312,8 +2034,7 @@ again:
          * flush, no worries.
          */
         raw_spin_lock(&logbuf_lock);
-        if (con_start != log_end)
-                retry = 1;
+        retry = console_seq != log_next_seq;
         raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 
         if (retry && console_trylock())
@@ -1549,7 +2270,9 @@ void register_console(struct console *newcon)
                  * for us.
                  */
                 raw_spin_lock_irqsave(&logbuf_lock, flags);
-                con_start = log_start;
+                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
@@ -1758,50 +2481,221 @@ int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 }
 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
  *
- * Iterate through each of the dump devices and call the oops/panic
- * callbacks with the log buffer.
+ * 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)
 {
-        unsigned long end;
-        unsigned chars;
         struct kmsg_dumper *dumper;
-        const char *s1, *s2;
-        unsigned long l1, l2;
         unsigned long flags;
 
         if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
                 return;
 
-        /* Theoretically, the log could move on after we do this, but
-           there's not a lot we can do about that. The new messages
-           will overwrite the start of what we dump. */
+        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);
-        end = log_end & LOG_BUF_MASK;
-        chars = logged_chars;
+        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, 0, 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
+ * @buf: 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;
+        enum log_flags prev;
+        size_t l = 0;
+        bool ret = false;
+
+        if (!dumper->active)
+                goto out;
 
-        if (chars > end) {
-                s1 = log_buf + log_buf_len - chars + end;
-                l1 = chars - end;
+        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;
+        }
 
-                s2 = log_buf;
-                l2 = end;
-        } else {
-                s1 = "";
-                l1 = 0;
+        /* last entry */
+        if (dumper->cur_seq >= dumper->next_seq) {
+                raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+                goto out;
+        }
 
-                s2 = log_buf + end - chars;
-                l2 = chars;
+        /* 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;
         }
 
-        rcu_read_lock();
-        list_for_each_entry_rcu(dumper, &dump_list, list)
-                dumper->dump(dumper, reason, s1, l1, s2, l2);
-        rcu_read_unlock();
+        /* 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);
+
+/**
+ * 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