tracedump: Dump ftrace ring buffer data

Add a new module that will dump the contents of the ftrace ring buffer.
Data is compressed and can be in ascii or binary form. Data will
automatically dump on kernel panic to console. Data can be dumped by
reading /proc/tracedump. See tracedump.h for details.

Change-Id: I7b7afc3def0b88629dd120d17e43858306a8f357
Signed-off-by: Liang Cheng <licheng@nvidia.com>
Reviewed-on: http://git-master/r/69494
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Dan Willemsen <dwillemsen@nvidia.com>

Rebase-Id: Rb7921bf859e968422af1a98b971415462d8c57f0

5 files changed, 808 insertions, 0 deletions

diff --git a/Documentation/trace/tracedump.txt b/Documentation/trace/tracedump.txt
new file mode 100644
index 000000000000..cba0decc3fc3
--- /dev/null
+++ b/Documentation/trace/tracedump.txt
@@ -0,0 +1,58 @@
+			     Tracedump
+
+		Documentation written by Alon Farchy
+
+1. Overview
+============
+
+The tracedump module provides additional mechanisms to retrieve tracing data.
+It can be used to retrieve traces after a kernel panic or while the system
+is running in either binary format or plaintext. The dumped data is compressed
+with zlib to conserve space.
+
+2. Configuration Options
+========================
+
+CONFIG_TRACEDUMP - enable the tracedump module.
+CONFIG_TRACEDUMP_PANIC - dump to console on kernel panic
+CONFIG_TRACEDUMP_PROCFS - add file /proc/tracedump for userspace access.
+
+3. Module Parameters
+====================
+
+format_ascii
+
+	If 1, data will dump in human-readable format, ordered by time.
+	If 0, data will be dumped as raw pages from the ring buffer,
+	ordered by CPU, followed by the saved cmdlines so that the
+	raw data can be decoded. Default: 0
+
+panic_size
+
+	Maximum amount of compressed data to dump during a kernel panic
+	in kilobytes. This only applies if format_ascii == 1. In this case,
+	tracedump will compress the data, check the size, and if it is too big
+	toss out some data, compress again, etc, until the size is below
+	panic_size. Default: 512KB
+
+compress_level
+
+	Determines the compression level that zlib will use. Available levels
+	are 0-9, with 0 as no compression and 9 as maximum compression.
+	Default: 9.
+
+4. Usage
+========
+
+If configured with CONFIG_TRACEDUMP_PROCFS, the tracing data can be pulled
+by reading from /proc/tracedump. For example:
+
+	# cat /proc/tracedump > my_tracedump
+
+Tracedump will surround the dump with a magic word (TRACEDUMP). Between the
+magic words is the compressed data, which can be decompressed with a standard
+zlib implementation. After decompression, if format_ascii == 1, then the
+output should be readable.
+
+If format_ascii == 0, the output should be in binary form, delimited by
+CPU_END. After the last CPU should be the saved cmdlines, delimited by |.
diff --git a/include/linux/tracedump.h b/include/linux/tracedump.h
new file mode 100644
index 000000000000..9e86946e354e
--- /dev/null
+++ b/include/linux/tracedump.h
@@ -0,0 +1,43 @@
+/*
+ * include/linux/tracedump.h
+ *
+ * Copyright (c) 2011, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#ifndef _LINUX_KERNEL_TRACEDUMP_H
+#define _LINUX_KERNEL_TRACEDUMP_H
+
+/* tracedump
+ * This module provides additional mechanisms for retreiving tracing data.
+ * For details on configurations, parameters and usage, see tracedump.txt.
+ */
+
+#define TD_NO_PRINT 0
+#define TD_PRINT_CONSOLE 1
+#define TD_PRINT_USER 2
+
+/* Dump the tracer to console */
+int tracedump_dump(size_t max_out);
+
+/* Dumping functions */
+int tracedump_init(void);
+ssize_t tracedump_all(int print_to);
+ssize_t tracedump_next(size_t max_out, int print_to);
+int tracedump_reset(void);
+int tracedump_deinit(void);
+
+#endif /* _LINUX_KERNEL_TRACEDUMP_H */
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 1c8ed74dcaf0..fd101e6f0190 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -582,6 +582,30 @@ config TRACELEVEL
 	  will automatically be enabled on kernel boot, and users can change
 	  the the trace level in a kernel parameter.
 
+config TRACEDUMP
+	bool "Dumping functionality for ftrace"
+	depends on FUNCTION_TRACER
+	help
+	  This option adds functionality to dump tracing data in several forms
+	  Data can be dumped in ascii form or as raw pages from the tracing
+	  ring buffers, along with the saved cmdlines. This is specified by
+	  the module parameter tracedump_ascii. Data will be compressed
+	  using zlib.
+
+config TRACEDUMP_PANIC
+	bool "Tracedump to console on panic"
+	depends on TRACEDUMP
+	help
+	  With this option, tracedump will automatically dump to the console
+	  on a kernel panic.
+
+config TRACEDUMP_PROCFS
+	bool "Tracedump via proc file"
+	depends on TRACEDUMP
+	help
+	  With this option, tracedump can be dumped from user space by reading
+	  from /proc/tracedump.
+
 endif # FTRACE
 
 endif # TRACING_SUPPORT
diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
index 45ef52cfb0b9..2ac813c96712 100644
--- a/kernel/trace/Makefile
+++ b/kernel/trace/Makefile
@@ -59,6 +59,7 @@ ifeq ($(CONFIG_TRACING),y)
 obj-$(CONFIG_KGDB_KDB) += trace_kdb.o
 endif
 obj-$(CONFIG_TRACELEVEL) += tracelevel.o
+obj-$(CONFIG_TRACEDUMP) += tracedump.o
 obj-$(CONFIG_PROBE_EVENTS) += trace_probe.o
 obj-$(CONFIG_UPROBE_EVENT) += trace_uprobe.o
 
diff --git a/kernel/trace/tracedump.c b/kernel/trace/tracedump.c
new file mode 100644
index 000000000000..8d9589faad82
--- /dev/null
+++ b/kernel/trace/tracedump.c
@@ -0,0 +1,682 @@
+/*
+ * kernel/trace/tracedump.c
+ *
+ * Copyright (c) 2011, NVIDIA CORPORATION.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <linux/console.h>
+#include <linux/cpumask.h>
+#include <linux/init.h>
+#include <linux/irqflags.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/proc_fs.h>
+#include <linux/ring_buffer.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/string.h>
+#include <linux/threads.h>
+#include <linux/tracedump.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/zlib.h>
+
+#include "trace.h"
+#include "trace_output.h"
+
+#define CPU_MAX (NR_CPUS-1)
+
+#define TRYM(fn, ...) do {		\
+	int try_error = (fn);		\
+	if (try_error < 0) {		\
+		printk(__VA_ARGS__);	\
+		return try_error;	\
+	}				\
+} while (0)
+
+#define TRY(fn) TRYM(fn, TAG "Caught error from %s in %s\n", #fn, __func__)
+
+/* Stolen from printk.c */
+#define for_each_console(con) \
+	for (con = console_drivers; con != NULL; con = con->next)
+
+#define TAG KERN_ERR "tracedump: "
+
+#define TD_MIN_CONSUME 2000
+#define TD_COMPRESS_CHUNK 0x8000
+
+static DEFINE_MUTEX(tracedump_proc_lock);
+
+static const char MAGIC_NUMBER[9] = "TRACEDUMP";
+static const char CPU_DELIM[7] = "CPU_END";
+#define CMDLINE_DELIM "|"
+
+/* Type of output */
+static bool current_format;
+static bool format_ascii;
+module_param(format_ascii, bool, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(format_ascii, "Dump ascii or raw data");
+
+/* Max size of output */
+static uint panic_size = 0x80000;
+module_param(panic_size, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(panic_size, "Max dump size during kernel panic (bytes)");
+
+static uint compress_level = 9;
+module_param(compress_level, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(compress_level, "Level of compression to use. [0-9]");
+
+static char out_buf[TD_COMPRESS_CHUNK];
+static z_stream stream;
+static int compress_done;
+static int flush;
+
+static int old_trace_flags;
+
+static struct trace_iterator iter;
+static struct pager_s {
+	struct trace_array	*tr;
+	void			*spare;
+	int			cpu;
+	int			len;
+	char __user		*ubuf;
+} pager;
+
+static char cmdline_buf[16+TASK_COMM_LEN];
+
+static int print_to_console(const char *buf, size_t len)
+{
+	struct console *con;
+
+	/* Stolen from printk.c */
+	for_each_console(con) {
+		if ((con->flags & CON_ENABLED) && con->write &&
+		   (cpu_online(smp_processor_id()) ||
+		   (con->flags & CON_ANYTIME)))
+			con->write(con, buf, len);
+	}
+	return 0;
+}
+
+static int print_to_user(const char *buf, size_t len)
+{
+	int size;
+	size = copy_to_user(pager.ubuf, buf, len);
+	if (size > 0) {
+		printk(TAG "Failed to copy to user %d bytes\n", size);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+static int print(const char *buf, size_t len, int print_to)
+{
+	if (print_to == TD_PRINT_CONSOLE)
+		TRY(print_to_console(buf, len));
+	else if (print_to == TD_PRINT_USER)
+		TRY(print_to_user(buf, len));
+	return 0;
+}
+
+/* print_magic will print MAGIC_NUMBER using the
+ * print function selected by print_to.
+ */
+static inline ssize_t print_magic(int print_to)
+{
+	print(MAGIC_NUMBER, sizeof(MAGIC_NUMBER), print_to);
+	return sizeof(MAGIC_NUMBER);
+}
+
+static int iter_init(void)
+{
+	int cpu;
+
+	/* Make iter point to global ring buffer used in trace. */
+	trace_init_global_iter(&iter);
+
+	/* Disable tracing */
+	for_each_tracing_cpu(cpu) {
+		atomic_inc(&iter.tr->data[cpu]->disabled);
+	}
+
+	/* Save flags */
+	old_trace_flags = trace_flags;
+
+	/* Dont look at memory in panic mode. */
+	trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
+
+	/* Prepare ring buffer iter */
+	for_each_tracing_cpu(cpu) {
+		iter.buffer_iter[cpu] =
+		 ring_buffer_read_prepare(iter.tr->buffer, cpu);
+	}
+	ring_buffer_read_prepare_sync();
+	for_each_tracing_cpu(cpu) {
+		ring_buffer_read_start(iter.buffer_iter[cpu]);
+		tracing_iter_reset(&iter, cpu);
+	}
+	return 0;
+}
+
+/* iter_next gets the next entry in the ring buffer, ordered by time.
+ * If there are no more entries, returns 0.
+ */
+static ssize_t iter_next(void)
+{
+	/* Zero out the iterator's seq */
+	memset(&iter.seq, 0,
+		sizeof(struct trace_iterator) -
+		offsetof(struct trace_iterator, seq));
+
+	while (!trace_empty(&iter)) {
+		if (trace_find_next_entry_inc(&iter) == NULL) {
+			printk(TAG "trace_find_next_entry failed!\n");
+			return -EINVAL;
+		}
+
+		/* Copy the ring buffer data to iterator's seq */
+		print_trace_line(&iter);
+		if (iter.seq.len != 0)
+			return iter.seq.len;
+	}
+	return 0;
+}
+
+static int iter_deinit(void)
+{
+	int cpu;
+	/* Enable tracing */
+	for_each_tracing_cpu(cpu) {
+		ring_buffer_read_finish(iter.buffer_iter[cpu]);
+	}
+	for_each_tracing_cpu(cpu) {
+		atomic_dec(&iter.tr->data[cpu]->disabled);
+	}
+
+	/* Restore flags */
+	trace_flags = old_trace_flags;
+	return 0;
+}
+
+static int pager_init(void)
+{
+	int cpu;
+
+	/* Need to do this to get a pointer to global_trace (iter.tr).
+	   Lame, I know. */
+	trace_init_global_iter(&iter);
+
+	/* Turn off tracing */
+	for_each_tracing_cpu(cpu) {
+		atomic_inc(&iter.tr->data[cpu]->disabled);
+	}
+
+	memset(&pager, 0, sizeof(pager));
+	pager.tr = iter.tr;
+	pager.len = TD_COMPRESS_CHUNK;
+
+	return 0;
+}
+
+/* pager_next_cpu moves the pager to the next cpu.
+ * Returns 0 if pager is done, else 1.
+ */
+static ssize_t pager_next_cpu(void)
+{
+	if (pager.cpu <= CPU_MAX) {
+		pager.cpu += 1;
+		return 1;
+	}
+
+	return 0;
+}
+
+/* pager_next gets the next page of data from the ring buffer
+ * of the current cpu. Returns page size or 0 if no more data.
+ */
+static ssize_t pager_next(void)
+{
+	int ret;
+
+	if (pager.cpu > CPU_MAX)
+		return 0;
+
+	if (!pager.spare)
+		pager.spare = ring_buffer_alloc_read_page(pager.tr->buffer);
+	if (!pager.spare) {
+		printk(TAG "ring_buffer_alloc_read_page failed!");
+		return -ENOMEM;
+	}
+
+	ret = ring_buffer_read_page(pager.tr->buffer,
+				    &pager.spare,
+				    pager.len,
+				    pager.cpu, 0);
+	if (ret < 0)
+		return 0;
+
+	return PAGE_SIZE;
+}
+
+static int pager_deinit(void)
+{
+	int cpu;
+	if (pager.spare != NULL)
+		ring_buffer_free_read_page(pager.tr->buffer, pager.spare);
+
+	for_each_tracing_cpu(cpu) {
+		atomic_dec(&iter.tr->data[cpu]->disabled);
+	}
+	return 0;
+}
+
+/* cmdline_next gets the next saved cmdline from the trace and
+ * puts it in cmdline_buf. Returns the size of the cmdline, or 0 if empty.
+ * but will reset itself on a subsequent call.
+ */
+static ssize_t cmdline_next(void)
+{
+	static int pid;
+	ssize_t size = 0;
+
+	if (pid >= PID_MAX_DEFAULT)
+		pid = -1;
+
+	while (size == 0 && pid < PID_MAX_DEFAULT) {
+		pid++;
+		trace_find_cmdline(pid, cmdline_buf);
+		if (!strncmp(cmdline_buf, "<...>", 5))
+			continue;
+
+		sprintf(&cmdline_buf[strlen(cmdline_buf)], " %d"
+				     CMDLINE_DELIM, pid);
+		size = strlen(cmdline_buf);
+	}
+	return size;
+}
+
+/* comsume_events removes the first 'num' entries from the ring buffer. */
+static int consume_events(size_t num)
+{
+	TRY(iter_init());
+	for (; num > 0 && !trace_empty(&iter); num--) {
+		trace_find_next_entry_inc(&iter);
+		ring_buffer_consume(iter.tr->buffer, iter.cpu, &iter.ts,
+				    &iter.lost_events);
+	}
+	TRY(iter_deinit());
+	return 0;
+}
+
+static int data_init(void)
+{
+	if (current_format)
+		TRY(iter_init());
+	else
+		TRY(pager_init());
+	return 0;
+}
+
+/* data_next will figure out the right 'next' function to
+ * call and will select the right buffer to pass back
+ * to compress_next.
+ *
+ * iter_next should be used to get data entry-by-entry, ordered
+ * by time, which is what we need in order to convert it to ascii.
+ *
+ * pager_next will return a full page of raw data at a time, one
+ * CPU at a time. pager_next_cpu must be called to get the next CPU.
+ * cmdline_next will get the next saved cmdline
+ */
+static ssize_t data_next(const char **buf)
+{
+	ssize_t size;
+
+	if (current_format) {
+		TRY(size = iter_next());
+		*buf = iter.seq.buffer;
+	} else {
+		TRY(size = pager_next());
+		*buf = pager.spare;
+		if (size == 0) {
+			if (pager_next_cpu()) {
+				size = sizeof(CPU_DELIM);
+				*buf = CPU_DELIM;
+			} else {
+				TRY(size = cmdline_next());
+				*buf = cmdline_buf;
+			}
+		}
+	}
+	return size;
+}
+
+static int data_deinit(void)
+{
+	if (current_format)
+		TRY(iter_deinit());
+	else
+		TRY(pager_deinit());
+	return 0;
+}
+
+static int compress_init(void)
+{
+	int workspacesize, ret;
+
+	compress_done = 0;
+	flush = Z_NO_FLUSH;
+	stream.data_type = current_format ? Z_ASCII : Z_BINARY;
+	workspacesize = zlib_deflate_workspacesize(MAX_WBITS, MAX_MEM_LEVEL);
+	stream.workspace = vmalloc(workspacesize);
+	if (!stream.workspace) {
+		printk(TAG "Could not allocate "
+			   "enough memory for zlib!\n");
+		return -ENOMEM;
+	}
+	memset(stream.workspace, 0, workspacesize);
+
+	ret = zlib_deflateInit(&stream, compress_level);
+	if (ret != Z_OK) {
+		printk(TAG "%s\n", stream.msg);
+		return ret;
+	}
+	stream.avail_in = 0;
+	stream.avail_out = 0;
+	TRY(data_init());
+	return 0;
+}
+
+/* compress_next will compress up to min(max_out, TD_COMPRESS_CHUNK) bytes
+ * of data into the output buffer. It gets the data by calling data_next.
+ * It will return the most data it possibly can. If it returns 0, then
+ * there is no more data.
+ *
+ * By the way that zlib works, each call to zlib_deflate will possibly
+ * consume up to avail_in bytes from next_in, and will fill up to
+ * avail_out bytes in next_out. Once flush == Z_FINISH, it can not take
+ * any more input. It will output until it is finished, and will return
+ * Z_STREAM_END.
+ */
+static ssize_t compress_next(size_t max_out)
+{
+	ssize_t ret;
+	max_out = min(max_out, (size_t)TD_COMPRESS_CHUNK);
+	stream.next_out = out_buf;
+	stream.avail_out = max_out;
+	while (stream.avail_out > 0 && !compress_done) {
+		if (stream.avail_in == 0 && flush != Z_FINISH) {
+			TRY(stream.avail_in =
+			    data_next((const char **)&stream.next_in));
+			flush = (stream.avail_in == 0) ? Z_FINISH : Z_NO_FLUSH;
+		}
+		if (stream.next_in != NULL) {
+			TRYM((ret = zlib_deflate(&stream, flush)),
+			     "zlib: %s\n", stream.msg);
+			compress_done = (ret == Z_STREAM_END);
+		}
+	}
+	ret = max_out - stream.avail_out;
+	return ret;
+}
+
+static int compress_deinit(void)
+{
+	TRY(data_deinit());
+
+	zlib_deflateEnd(&stream);
+	vfree(stream.workspace);
+
+	/* TODO: remove */
+	printk(TAG "Total in: %ld\n", stream.total_in);
+	printk(TAG "Total out: %ld\n", stream.total_out);
+	return stream.total_out;
+}
+
+static int compress_reset(void)
+{
+	TRY(compress_deinit());
+	TRY(compress_init());
+	return 0;
+}
+
+/* tracedump_init initializes all tracedump components.
+ * Call this before tracedump_next
+ */
+int tracedump_init(void)
+{
+	TRY(compress_init());
+	return 0;
+}
+
+/* tracedump_next will print up to max_out data from the tracing ring
+ * buffers using the print function selected by print_to. The data is
+ * compressed using zlib.
+ *
+ * The output type of the data is specified by the format_ascii module
+ * parameter. If format_ascii == 1, human-readable data will be output.
+ * Otherwise, it will output raw data from the ring buffer in cpu order,
+ * followed by the saved_cmdlines data.
+ */
+ssize_t tracedump_next(size_t max_out, int print_to)
+{
+	ssize_t size;
+	TRY(size = compress_next(max_out));
+	print(out_buf, size, print_to);
+	return size;
+}
+
+/* tracedump_all will print all data in the tracing ring buffers using
+ * the print function selected by print_to. The data is compressed using
+ * zlib, and is surrounded by MAGIC_NUMBER.
+ *
+ * The output type of the data is specified by the format_ascii module
+ * parameter. If format_ascii == 1, human-readable data will be output.
+ * Otherwise, it will output raw data from the ring buffer in cpu order,
+ * followed by the saved_cmdlines data.
+ */
+ssize_t tracedump_all(int print_to)
+{
+	ssize_t ret, size = 0;
+	TRY(size += print_magic(print_to));
+
+	do {
+		/* Here the size used doesn't really matter,
+		 * since we're dumping everything. */
+		TRY(ret = tracedump_next(0xFFFFFFFF, print_to));
+		size += ret;
+	} while (ret > 0);
+
+	TRY(size += print_magic(print_to));
+
+	return size;
+}
+
+/* tracedump_deinit deinitializes all tracedump components.
+ * This must be called, even on error.
+ */
+int tracedump_deinit(void)
+{
+	TRY(compress_deinit());
+	return 0;
+}
+
+/* tracedump_reset reinitializes all tracedump components. */
+int tracedump_reset(void)
+{
+	TRY(compress_reset());
+	return 0;
+}
+
+
+
+/* tracedump_open opens the tracedump file for reading. */
+static int tracedump_open(struct inode *inode, struct file *file)
+{
+	int ret;
+	mutex_lock(&tracedump_proc_lock);
+	current_format = format_ascii;
+	ret = tracedump_init();
+	if (ret < 0)
+		goto err;
+
+	ret = nonseekable_open(inode, file);
+	if (ret < 0)
+		goto err;
+	return ret;
+
+err:
+	mutex_unlock(&tracedump_proc_lock);
+	return ret;
+}
+
+/* tracedump_read will reads data from tracedump_next and prints
+ * it to userspace. It will surround the data with MAGIC_NUMBER.
+ */
+static ssize_t tracedump_read(struct file *file, char __user *buf,
+			      size_t len, loff_t *offset)
+{
+	static int done;
+	ssize_t size = 0;
+
+	pager.ubuf = buf;
+
+	if (*offset == 0) {
+		done = 0;
+		TRY(size = print_magic(TD_PRINT_USER));
+	} else if (!done) {
+		TRY(size = tracedump_next(len, TD_PRINT_USER));
+		if (size == 0) {
+			TRY(size = print_magic(TD_PRINT_USER));
+			done = 1;
+		}
+	}
+
+	*offset += size;
+
+	return size;
+}
+
+static int tracedump_release(struct inode *inode, struct file *file)
+{
+	int ret;
+	ret = tracedump_deinit();
+	mutex_unlock(&tracedump_proc_lock);
+	return ret;
+}
+
+/* tracedump_dump dumps all tracing data from the tracing ring buffers
+ * to all consoles. For details about the output format, see
+ * tracedump_all.
+
+ * At most max_out bytes are dumped. To accomplish this,
+ * tracedump_dump calls tracedump_all several times without writing the data,
+ * each time tossing out old data until it reaches its goal.
+ *
+ * Note: dumping raw pages currently does NOT follow the size limit.
+ */
+
+int tracedump_dump(size_t max_out)
+{
+	ssize_t size;
+	size_t consume;
+
+	printk(TAG "\n");
+
+	tracedump_init();
+
+	if (format_ascii) {
+		size = tracedump_all(TD_NO_PRINT);
+		if (size < 0) {
+			printk(TAG "failed to dump\n");
+			goto out;
+		}
+		while (size > max_out) {
+			TRY(tracedump_deinit());
+			/* Events take more or less 60 ascii bytes each,
+			   not counting compression */
+			consume = TD_MIN_CONSUME + (size - max_out) /
+					(60 / (compress_level + 1));
+			TRY(consume_events(consume));
+			TRY(tracedump_init());
+			size = tracedump_all(TD_NO_PRINT);
+			if (size < 0) {
+				printk(TAG "failed to dump\n");
+				goto out;
+			}
+		}
+
+		TRY(tracedump_reset());
+	}
+	size = tracedump_all(TD_PRINT_CONSOLE);
+	if (size < 0) {
+		printk(TAG "failed to dump\n");
+		goto out;
+	}
+
+out:
+	tracedump_deinit();
+	printk(KERN_INFO "\n" TAG " end\n");
+	return size;
+}
+
+static const struct file_operations tracedump_fops = {
+	.owner = THIS_MODULE,
+	.open = tracedump_open,
+	.read = tracedump_read,
+	.release = tracedump_release,
+};
+
+#ifdef CONFIG_TRACEDUMP_PANIC
+static int tracedump_panic_handler(struct notifier_block *this,
+				   unsigned long event, void *unused)
+{
+	tracedump_dump(panic_size);
+	return 0;
+}
+
+static struct notifier_block tracedump_panic_notifier = {
+	.notifier_call	= tracedump_panic_handler,
+	.next		= NULL,
+	.priority	= 150   /* priority: INT_MAX >= x >= 0 */
+};
+#endif
+
+static int __init tracedump_initcall(void)
+{
+#ifdef CONFIG_TRACEDUMP_PROCFS
+	struct proc_dir_entry *entry;
+
+	/* Create a procfs file for easy dumping */
+	entry = create_proc_entry("tracedump", S_IFREG | S_IRUGO, NULL);
+	if (!entry)
+		printk(TAG "failed to create proc entry\n");
+	else
+		entry->proc_fops = &tracedump_fops;
+#endif
+
+#ifdef CONFIG_TRACEDUMP_PANIC
+	/* Automatically dump to console on a kernel panic */
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &tracedump_panic_notifier);
+#endif
+	return 0;
+}
+
+early_initcall(tracedump_initcall);