Merge tag 'driver-core-3.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core updates from Greg Kroah-Hartman:
 "Here's the driver core, and other driver subsystems, pull request for
  the 3.5-rc1 merge window.

  Outside of a few minor driver core changes, we ended up with the
  following different subsystem and core changes as well, due to
  interdependancies on the driver core:
   - hyperv driver updates
   - drivers/memory being created and some drivers moved into it
   - extcon driver subsystem created out of the old Android staging
     switch driver code
   - dynamic debug updates
   - printk rework, and /dev/kmsg changes

  All of this has been tested in the linux-next releases for a few weeks
  with no reported problems.

  Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>"

Fix up conflicts in drivers/extcon/extcon-max8997.c where git noticed
that a patch to the deleted drivers/misc/max8997-muic.c driver needs to
be applied to this one.

* tag 'driver-core-3.5-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (90 commits)
  uio_pdrv_genirq: get irq through platform resource if not set otherwise
  memory: tegra{20,30}-mc: Remove empty *_remove()
  printk() - isolate KERN_CONT users from ordinary complete lines
  sysfs: get rid of some lockdep false positives
  Drivers: hv: util: Properly handle version negotiations.
  Drivers: hv: Get rid of an unnecessary check in vmbus_prep_negotiate_resp()
  memory: tegra{20,30}-mc: Use dev_err_ratelimited()
  driver core: Add dev_*_ratelimited() family
  Driver Core: don't oops with unregistered driver in driver_find_device()
  printk() - restore prefix/timestamp printing for multi-newline strings
  printk: add stub for prepend_timestamp()
  ARM: tegra30: Make MC optional in Kconfig
  ARM: tegra20: Make MC optional in Kconfig
  ARM: tegra30: MC: Remove unnecessary BUG*()
  ARM: tegra20: MC: Remove unnecessary BUG*()
  printk: correctly align __log_buf
  ARM: tegra30: Add Tegra Memory Controller(MC) driver
  ARM: tegra20: Add Tegra Memory Controller(MC) driver
  printk() - restore timestamp printing at console output
  printk() - do not merge continuation lines of different threads
  ...

3 files changed, 994 insertions, 460 deletions

diff --git a/kernel/module.c b/kernel/module.c
index 78ac6ec1e425..a4e60973ca73 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2953,7 +2953,7 @@ static struct module *load_module(void __user *umod,
 
 	/* Module is ready to execute: parsing args may do that. */
 	err = parse_args(mod->name, mod->args, mod->kp, mod->num_kp,
-			 -32768, 32767, NULL);
+			 -32768, 32767, &ddebug_dyndbg_module_param_cb);
 	if (err < 0)
 		goto unlink;
 
diff --git a/kernel/params.c b/kernel/params.c
index f37d82631347..ed35345be536 100644
--- a/kernel/params.c
+++ b/kernel/params.c
@@ -85,11 +85,13 @@ bool parameq(const char *a, const char *b)
 
 static int parse_one(char *param,
 		     char *val,
+		     const char *doing,
 		     const struct kernel_param *params,
 		     unsigned num_params,
 		     s16 min_level,
 		     s16 max_level,
-		     int (*handle_unknown)(char *param, char *val))
+		     int (*handle_unknown)(char *param, char *val,
+				     const char *doing))
 {
 	unsigned int i;
 	int err;
@@ -104,8 +106,8 @@ static int parse_one(char *param,
 			if (!val && params[i].ops->set != param_set_bool
 			    && params[i].ops->set != param_set_bint)
 				return -EINVAL;
-			pr_debug("They are equal!  Calling %p\n",
-			       params[i].ops->set);
+			pr_debug("handling %s with %p\n", param,
+				params[i].ops->set);
 			mutex_lock(&param_lock);
 			err = params[i].ops->set(val, &params[i]);
 			mutex_unlock(&param_lock);
@@ -114,11 +116,11 @@ static int parse_one(char *param,
 	}
 
 	if (handle_unknown) {
-		pr_debug("Unknown argument: calling %p\n", handle_unknown);
-		return handle_unknown(param, val);
+		pr_debug("doing %s: %s='%s'\n", doing, param, val);
+		return handle_unknown(param, val, doing);
 	}
 
-	pr_debug("Unknown argument `%s'\n", param);
+	pr_debug("Unknown argument '%s'\n", param);
 	return -ENOENT;
 }
 
@@ -175,49 +177,47 @@ static char *next_arg(char *args, char **param, char **val)
 }
 
 /* Args looks like "foo=bar,bar2 baz=fuz wiz". */
-int parse_args(const char *name,
+int parse_args(const char *doing,
 	       char *args,
 	       const struct kernel_param *params,
 	       unsigned num,
 	       s16 min_level,
 	       s16 max_level,
-	       int (*unknown)(char *param, char *val))
+	       int (*unknown)(char *param, char *val, const char *doing))
 {
 	char *param, *val;
 
-	pr_debug("Parsing ARGS: %s\n", args);
-
 	/* Chew leading spaces */
 	args = skip_spaces(args);
 
+	if (*args)
+		pr_debug("doing %s, parsing ARGS: '%s'\n", doing, args);
+
 	while (*args) {
 		int ret;
 		int irq_was_disabled;
 
 		args = next_arg(args, &param, &val);
 		irq_was_disabled = irqs_disabled();
-		ret = parse_one(param, val, params, num,
+		ret = parse_one(param, val, doing, params, num,
 				min_level, max_level, unknown);
-		if (irq_was_disabled && !irqs_disabled()) {
-			printk(KERN_WARNING "parse_args(): option '%s' enabled "
-					"irq's!\n", param);
-		}
+		if (irq_was_disabled && !irqs_disabled())
+			pr_warn("%s: option '%s' enabled irq's!\n",
+				doing, param);
+
 		switch (ret) {
 		case -ENOENT:
-			printk(KERN_ERR "%s: Unknown parameter `%s'\n",
-			       name, param);
+			pr_err("%s: Unknown parameter `%s'\n", doing, param);
 			return ret;
 		case -ENOSPC:
-			printk(KERN_ERR
-			       "%s: `%s' too large for parameter `%s'\n",
-			       name, val ?: "", param);
+			pr_err("%s: `%s' too large for parameter `%s'\n",
+			       doing, val ?: "", param);
 			return ret;
 		case 0:
 			break;
 		default:
-			printk(KERN_ERR
-			       "%s: `%s' invalid for parameter `%s'\n",
-			       name, val ?: "", param);
+			pr_err("%s: `%s' invalid for parameter `%s'\n",
+			       doing, val ?: "", param);
 			return ret;
 		}
 	}
@@ -263,8 +263,7 @@ STANDARD_PARAM_DEF(ulong, unsigned long, "%lu", unsigned long, strict_strtoul);
 int param_set_charp(const char *val, const struct kernel_param *kp)
 {
 	if (strlen(val) > 1024) {
-		printk(KERN_ERR "%s: string parameter too long\n",
-		       kp->name);
+		pr_err("%s: string parameter too long\n", kp->name);
 		return -ENOSPC;
 	}
 
@@ -400,8 +399,7 @@ static int param_array(const char *name,
 		int len;
 
 		if (*num == max) {
-			printk(KERN_ERR "%s: can only take %i arguments\n",
-			       name, max);
+			pr_err("%s: can only take %i arguments\n", name, max);
 			return -EINVAL;
 		}
 		len = strcspn(val, ",");
@@ -420,8 +418,7 @@ static int param_array(const char *name,
 	} while (save == ',');
 
 	if (*num < min) {
-		printk(KERN_ERR "%s: needs at least %i arguments\n",
-		       name, min);
+		pr_err("%s: needs at least %i arguments\n", name, min);
 		return -EINVAL;
 	}
 	return 0;
@@ -480,7 +477,7 @@ int param_set_copystring(const char *val, const struct kernel_param *kp)
 	const struct kparam_string *kps = kp->str;
 
 	if (strlen(val)+1 > kps->maxlen) {
-		printk(KERN_ERR "%s: string doesn't fit in %u chars.\n",
+		pr_err("%s: string doesn't fit in %u chars.\n",
 		       kp->name, kps->maxlen-1);
 		return -ENOSPC;
 	}
@@ -750,11 +747,8 @@ static struct module_kobject * __init locate_module_kobject(const char *name)
 #endif
 		if (err) {
 			kobject_put(&mk->kobj);
-			printk(KERN_ERR
-				"Module '%s' failed add to sysfs, error number %d\n",
+			pr_crit("Adding module '%s' to sysfs failed (%d), the system may be unstable.\n",
 				name, err);
-			printk(KERN_ERR
-				"The system will be unstable now.\n");
 			return NULL;
 		}
 
diff --git a/kernel/printk.c b/kernel/printk.c
index b663c2c95d39..32462d2b364a 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 +126,491 @@ 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
 
-static char __log_buf[__LOG_BUF_LEN];
+/* record buffer */
+#if !defined(CONFIG_64BIT) || defined(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)
+#define LOG_ALIGN 4
+#else
+#define LOG_ALIGN 8
+#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,
+		      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;
+
+	mutex_lock(&user->lock);
+	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
 /*
@@ -165,9 +624,9 @@ 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 +650,6 @@ 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 +677,8 @@ 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 +778,202 @@ 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_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++;
+		}
+		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 in 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)
 {
-	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 +1001,14 @@ 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:
@@ -399,52 +1022,11 @@ 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;
-		break;
+		syslog_print_all(NULL, 0, true);
 	/* Disable logging to console */
 	case SYSLOG_ACTION_CONSOLE_OFF:
 		if (saved_console_loglevel == -1)
@@ -472,7 +1054,35 @@ 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;
+		}
+		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:
@@ -501,29 +1111,11 @@ 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 +1132,33 @@ 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 +1183,6 @@ 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 +1195,6 @@ 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 +1238,12 @@ 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 +1259,23 @@ static inline void printk_delay(void)
 	}
 }
 
-asmlinkage int vprintk(const char *fmt, va_list args)
+asmlinkage int vprintk_emit(int facility, int level,
+			    const char *dict, size_t dictlen,
+			    const char *fmt, va_list args)
 {
-	int printed_len = 0;
-	int current_log_level = default_message_loglevel;
+	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;
-	char *p;
-	size_t plen;
-	char special;
+	bool newline = false;
+	bool prefix = false;
+	int printed_len = 0;
 
 	boot_delay_msec();
 	printk_delay();
@@ -856,7 +1287,7 @@ 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 +1304,110 @@ 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, 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--;
+		newline = true;
+	}
 
-		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 */
+			prefix = true;
+		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) {
+		prefix = true;
+		newline = true;
+	}
 
-			if (!*p)
-				break;
+	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;
 		}
 
-		emit_log_char(*p);
-		if (*p == '\n')
-			new_text_line = 1;
+		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 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 +1418,81 @@ 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 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)
@@ -1217,7 +1726,7 @@ 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 +1762,10 @@ 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;
+
 /**
  * console_unlock - unlock the console system
  *
@@ -1263,15 +1776,16 @@ 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 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);
@@ -1281,17 +1795,38 @@ void console_unlock(void)
 	console_may_schedule = 0;
 
 again:
-	for ( ; ; ) {
+	for (;;) {
+		struct log *msg;
+		static char text[LOG_LINE_MAX];
+		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;
+		}
+
+		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(_con_start, _log_end);
+		call_console_drivers(level, text, len);
 		start_critical_timings();
 		local_irq_restore(flags);
 	}
@@ -1312,8 +1847,7 @@ 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 +2083,8 @@ 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;
 		raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 		/*
 		 * We're about to replay the log buffer.  Only do this to the
@@ -1758,6 +2293,9 @@ 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
@@ -1767,8 +2305,7 @@ EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
  */
 void kmsg_dump(enum kmsg_dump_reason reason)
 {
-	unsigned long end;
-	unsigned chars;
+	u64 idx;
 	struct kmsg_dumper *dumper;
 	const char *s1, *s2;
 	unsigned long l1, l2;
@@ -1780,24 +2317,27 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 	/* 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. */
+
 	raw_spin_lock_irqsave(&logbuf_lock, flags);
-	end = log_end & LOG_BUF_MASK;
-	chars = logged_chars;
-	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
+	if (syslog_seq < log_first_seq)
+		idx = syslog_idx;
+	else
+		idx = log_first_idx;
 
-	if (chars > end) {
-		s1 = log_buf + log_buf_len - chars + end;
-		l1 = chars - end;
+	if (idx > log_next_idx) {
+		s1 = log_buf;
+		l1 = log_next_idx;
 
-		s2 = log_buf;
-		l2 = end;
+		s2 = log_buf + idx;
+		l2 = log_buf_len - idx;
 	} else {
 		s1 = "";
 		l1 = 0;
 
-		s2 = log_buf + end - chars;
-		l2 = chars;
+		s2 = log_buf + idx;
+		l2 = log_next_idx - idx;
 	}
+	raw_spin_unlock_irqrestore(&logbuf_lock, flags);
 
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list)