trace_functions.c

// SPDX-License-Identifier: GPL-2.0
/*
 * ring buffer based function tracer
 *
 * Copyright (C) 2007-2008 Steven Rostedt <srostedt@redhat.com>
 * Copyright (C) 2008 Ingo Molnar <mingo@redhat.com>
 *
 * Based on code from the latency_tracer, that is:
 *
 *  Copyright (C) 2004-2006 Ingo Molnar
 *  Copyright (C) 2004 Nadia Yvette Chambers
 */
#include <linux/ring_buffer.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/ftrace.h>
#include <linux/slab.h>
#include <linux/fs.h>

#include "trace.h"

static void tracing_start_function_trace(struct trace_array *tr);
static void tracing_stop_function_trace(struct trace_array *tr);
static void
function_trace_call(unsigned long ip, unsigned long parent_ip,
		    struct ftrace_ops *op, struct ftrace_regs *fregs);
static void
function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
			  struct ftrace_ops *op, struct ftrace_regs *fregs);
static void
function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
			       struct ftrace_ops *op, struct ftrace_regs *fregs);
static void
function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
				     struct ftrace_ops *op,
				     struct ftrace_regs *fregs);
static struct tracer_flags func_flags;

/* Our option */
enum {

	TRACE_FUNC_NO_OPTS		= 0x0, /* No flags set. */
	TRACE_FUNC_OPT_STACK		= 0x1,
	TRACE_FUNC_OPT_NO_REPEATS	= 0x2,

	/* Update this to next highest bit. */
	TRACE_FUNC_OPT_HIGHEST_BIT	= 0x4
};

#define TRACE_FUNC_OPT_MASK	(TRACE_FUNC_OPT_HIGHEST_BIT - 1)

int ftrace_allocate_ftrace_ops(struct trace_array *tr)
{
	struct ftrace_ops *ops;

	/* The top level array uses the "global_ops" */
	if (tr->flags & TRACE_ARRAY_FL_GLOBAL)
		return 0;

	ops = kzalloc(sizeof(*ops), GFP_KERNEL);
	if (!ops)
		return -ENOMEM;

	/* Currently only the non stack version is supported */
	ops->func = function_trace_call;
	ops->flags = FTRACE_OPS_FL_PID;

	tr->ops = ops;
	ops->private = tr;

	return 0;
}

void ftrace_free_ftrace_ops(struct trace_array *tr)
{
	kfree(tr->ops);
	tr->ops = NULL;
}

int ftrace_create_function_files(struct trace_array *tr,
				 struct dentry *parent)
{
	/*
	 * The top level array uses the "global_ops", and the files are
	 * created on boot up.
	 */
	if (tr->flags & TRACE_ARRAY_FL_GLOBAL)
		return 0;

	if (!tr->ops)
		return -EINVAL;

	ftrace_create_filter_files(tr->ops, parent);

	return 0;
}

void ftrace_destroy_function_files(struct trace_array *tr)
{
	ftrace_destroy_filter_files(tr->ops);
	ftrace_free_ftrace_ops(tr);
}

static ftrace_func_t select_trace_function(u32 flags_val)
{
	switch (flags_val & TRACE_FUNC_OPT_MASK) {
	case TRACE_FUNC_NO_OPTS:
		return function_trace_call;
	case TRACE_FUNC_OPT_STACK:
		return function_stack_trace_call;
	case TRACE_FUNC_OPT_NO_REPEATS:
		return function_no_repeats_trace_call;
	case TRACE_FUNC_OPT_STACK | TRACE_FUNC_OPT_NO_REPEATS:
		return function_stack_no_repeats_trace_call;
	default:
		return NULL;
	}
}

static bool handle_func_repeats(struct trace_array *tr, u32 flags_val)
{
	if (!tr->last_func_repeats &&
	    (flags_val & TRACE_FUNC_OPT_NO_REPEATS)) {
		tr->last_func_repeats = alloc_percpu(struct trace_func_repeats);
		if (!tr->last_func_repeats)
			return false;
	}

	return true;
}

static int function_trace_init(struct trace_array *tr)
{
	ftrace_func_t func;
	/*
	 * Instance trace_arrays get their ops allocated
	 * at instance creation. Unless it failed
	 * the allocation.
	 */
	if (!tr->ops)
		return -ENOMEM;

	func = select_trace_function(func_flags.val);
	if (!func)
		return -EINVAL;

	if (!handle_func_repeats(tr, func_flags.val))
		return -ENOMEM;

	ftrace_init_array_ops(tr, func);

	tr->array_buffer.cpu = raw_smp_processor_id();

	tracing_start_cmdline_record();
	tracing_start_function_trace(tr);
	return 0;
}

static void function_trace_reset(struct trace_array *tr)
{
	tracing_stop_function_trace(tr);
	tracing_stop_cmdline_record();
	ftrace_reset_array_ops(tr);
}

static void function_trace_start(struct trace_array *tr)
{
	tracing_reset_online_cpus(&tr->array_buffer);
}

static void
function_trace_call(unsigned long ip, unsigned long parent_ip,
		    struct ftrace_ops *op, struct ftrace_regs *fregs)
{
	struct trace_array *tr = op->private;
	struct trace_array_cpu *data;
	unsigned int trace_ctx;
	int bit;
	int cpu;

	if (unlikely(!tr->function_enabled))
		return;

	bit = ftrace_test_recursion_trylock(ip, parent_ip);
	if (bit < 0)
		return;

	trace_ctx = tracing_gen_ctx();

	cpu = smp_processor_id();
	data = per_cpu_ptr(tr->array_buffer.data, cpu);
	if (!atomic_read(&data->disabled))
		trace_function(tr, ip, parent_ip, trace_ctx);

	ftrace_test_recursion_unlock(bit);
}

#ifdef CONFIG_UNWINDER_ORC
/*
 * Skip 2:
 *
 *   function_stack_trace_call()
 *   ftrace_call()
 */
#define STACK_SKIP 2
#else
/*
 * Skip 3:
 *   __trace_stack()
 *   function_stack_trace_call()
 *   ftrace_call()
 */
#define STACK_SKIP 3
#endif

static void
function_stack_trace_call(unsigned long ip, unsigned long parent_ip,
			  struct ftrace_ops *op, struct ftrace_regs *fregs)
{
	struct trace_array *tr = op->private;
	struct trace_array_cpu *data;
	unsigned long flags;
	long disabled;
	int cpu;
	unsigned int trace_ctx;

	if (unlikely(!tr->function_enabled))
		return;

	/*
	 * Need to use raw, since this must be called before the
	 * recursive protection is performed.
	 */
	local_irq_save(flags);
	cpu = raw_smp_processor_id();
	data = per_cpu_ptr(tr->array_buffer.data, cpu);
	disabled = atomic_inc_return(&data->disabled);

	if (likely(disabled == 1)) {
		trace_ctx = tracing_gen_ctx_flags(flags);
		trace_function(tr, ip, parent_ip, trace_ctx);
		__trace_stack(tr, trace_ctx, STACK_SKIP);
	}

	atomic_dec(&data->disabled);
	local_irq_restore(flags);
}

static inline bool is_repeat_check(struct trace_array *tr,
				   struct trace_func_repeats *last_info,
				   unsigned long ip, unsigned long parent_ip)
{
	if (last_info->ip == ip &&
	    last_info->parent_ip == parent_ip &&
	    last_info->count < U16_MAX) {
		last_info->ts_last_call =
			ring_buffer_time_stamp(tr->array_buffer.buffer);
		last_info->count++;
		return true;
	}

	return false;
}

static inline void process_repeats(struct trace_array *tr,
				   unsigned long ip, unsigned long parent_ip,
				   struct trace_func_repeats *last_info,
				   unsigned int trace_ctx)
{
	if (last_info->count) {
		trace_last_func_repeats(tr, last_info, trace_ctx);
		last_info->count = 0;
	}

	last_info->ip = ip;
	last_info->parent_ip = parent_ip;
}

static void
function_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
			       struct ftrace_ops *op,
			       struct ftrace_regs *fregs)
{
	struct trace_func_repeats *last_info;
	struct trace_array *tr = op->private;
	struct trace_array_cpu *data;
	unsigned int trace_ctx;
	unsigned long flags;
	int bit;
	int cpu;

	if (unlikely(!tr->function_enabled))
		return;

	bit = ftrace_test_recursion_trylock(ip, parent_ip);
	if (bit < 0)
		return;

	cpu = smp_processor_id();
	data = per_cpu_ptr(tr->array_buffer.data, cpu);
	if (atomic_read(&data->disabled))
		goto out;

	/*
	 * An interrupt may happen at any place here. But as far as I can see,
	 * the only damage that this can cause is to mess up the repetition
	 * counter without valuable data being lost.
	 * TODO: think about a solution that is better than just hoping to be
	 * lucky.
	 */
	last_info = per_cpu_ptr(tr->last_func_repeats, cpu);
	if (is_repeat_check(tr, last_info, ip, parent_ip))
		goto out;

	local_save_flags(flags);
	trace_ctx = tracing_gen_ctx_flags(flags);
	process_repeats(tr, ip, parent_ip, last_info, trace_ctx);

	trace_function(tr, ip, parent_ip, trace_ctx);

out:
	ftrace_test_recursion_unlock(bit);
}

static void
function_stack_no_repeats_trace_call(unsigned long ip, unsigned long parent_ip,
				     struct ftrace_ops *op,
				     struct ftrace_regs *fregs)
{
	struct trace_func_repeats *last_info;
	struct trace_array *tr = op->private;
	struct trace_array_cpu *data;
	unsigned long flags;
	long disabled;
	int cpu;
	unsigned int trace_ctx;

	if (unlikely(!tr->function_enabled))
		return;

	/*
	 * Need to use raw, since this must be called before the
	 * recursive protection is performed.
	 */
	local_irq_save(flags);
	cpu = raw_smp_processor_id();
	data = per_cpu_ptr(tr->array_buffer.data, cpu);
	disabled = atomic_inc_return(&data->disabled);

	if (likely(disabled == 1)) {
		last_info = per_cpu_ptr(tr->last_func_repeats, cpu);
		if (is_repeat_check(tr, last_info, ip, parent_ip))
			goto out;

		trace_ctx = tracing_gen_ctx_flags(flags);
		process_repeats(tr, ip, parent_ip, last_info, trace_ctx);

		trace_function(tr, ip, parent_ip, trace_ctx);
		__trace_stack(tr, trace_ctx, STACK_SKIP);
	}

 out:
	atomic_dec(&data->disabled);
	local_irq_restore(flags);
}

static struct tracer_opt func_opts[] = {
#ifdef CONFIG_STACKTRACE
	{ TRACER_OPT(func_stack_trace, TRACE_FUNC_OPT_STACK) },
#endif
	{ TRACER_OPT(func-no-repeats, TRACE_FUNC_OPT_NO_REPEATS) },
	{ } /* Always set a last empty entry */
};

static struct tracer_flags func_flags = {
	.val = TRACE_FUNC_NO_OPTS, /* By default: all flags disabled */
	.opts = func_opts
};

static void tracing_start_function_trace(struct trace_array *tr)
{
	tr->function_enabled = 0;
	register_ftrace_function(tr->ops);
	tr->function_enabled = 1;
}

static void tracing_stop_function_trace(struct trace_array *tr)
{
	tr->function_enabled = 0;
	unregister_ftrace_function(tr->ops);
}

static struct tracer function_trace;

static int
func_set_flag(struct trace_array *tr, u32 old_flags, u32 bit, int set)
{
	ftrace_func_t func;
	u32 new_flags;

	/* Do nothing if already set. */
	if (!!set == !!(func_flags.val & bit))
		return 0;

	/* We can change this flag only when not running. */
	if (tr->current_trace != &function_trace)
		return 0;

	new_flags = (func_flags.val & ~bit) | (set ? bit : 0);
	func = select_trace_function(new_flags);
	if (!func)
		return -EINVAL;

	/* Check if there's anything to change. */
	if (tr->ops->func == func)
		return 0;

	if (!handle_func_repeats(tr, new_flags))
		return -ENOMEM;

	unregister_ftrace_function(tr->ops);
	tr->ops->func = func;
	register_ftrace_function(tr->ops);

	return 0;
}

static struct tracer function_trace __tracer_data =
{
	.name		= "function",
	.init		= function_trace_init,
	.reset		= function_trace_reset,
	.start		= function_trace_start,
	.flags		= &func_flags,
	.set_flag	= func_set_flag,
	.allow_instances = true,
#ifdef CONFIG_FTRACE_SELFTEST
	.selftest	= trace_selftest_startup_function,
#endif
};

#ifdef CONFIG_DYNAMIC_FTRACE
static void update_traceon_count(struct ftrace_probe_ops *ops,
				 unsigned long ip,
				 struct trace_array *tr, bool on,
				 void *data)
{
	struct ftrace_func_mapper *mapper = data;
	long *count;
	long old_count;

	/*
	 * Tracing gets disabled (or enabled) once per count.
	 * This function can be called at the same time on multiple CPUs.
	 * It is fine if both disable (or enable) tracing, as disabling
	 * (or enabling) the second time doesn't do anything as the
	 * state of the tracer is already disabled (or enabled).
	 * What needs to be synchronized in this case is that the count
	 * only gets decremented once, even if the tracer is disabled
	 * (or enabled) twice, as the second one is really a nop.
	 *
	 * The memory barriers guarantee that we only decrement the
	 * counter once. First the count is read to a local variable
	 * and a read barrier is used to make sure that it is loaded
	 * before checking if the tracer is in the state we want.
	 * If the tracer is not in the state we want, then the count
	 * is guaranteed to be the old count.
	 *
	 * Next the tracer is set to the state we want (disabled or enabled)
	 * then a write memory barrier is used to make sure that
	 * the new state is visible before changing the counter by
	 * one minus the old counter. This guarantees that another CPU
	 * executing this code will see the new state before seeing
	 * the new counter value, and would not do anything if the new
	 * counter is seen.
	 *
	 * Note, there is no synchronization between this and a user
	 * setting the tracing_on file. But we currently don't care
	 * about that.
	 */
	count = (long *)ftrace_func_mapper_find_ip(mapper, ip);
	old_count = *count;

	if (old_count <= 0)
		return;

	/* Make sure we see count before checking tracing state */
	smp_rmb();

	if (on == !!tracer_tracing_is_on(tr))
		return;

	if (on)
		tracer_tracing_on(tr);
	else
		tracer_tracing_off(tr);

	/* Make sure tracing state is visible before updating count */
	smp_wmb();

	*count = old_count - 1;
}

static void
ftrace_traceon_count(unsigned long ip, unsigned long parent_ip,
		     struct trace_array *tr, struct ftrace_probe_ops *ops,
		     void *data)
{
	update_traceon_count(ops, ip, tr, 1, data);
}

static void
ftrace_traceoff_count(unsigned long ip, unsigned long parent_ip,
		      struct trace_array *tr, struct ftrace_probe_ops *ops,
		      void *data)
{
	update_traceon_count(ops, ip, tr, 0, data);
}

static void
ftrace_traceon(unsigned long ip, unsigned long parent_ip,
	       struct trace_array *tr, struct ftrace_probe_ops *ops,
	       void *data)
{
	if (tracer_tracing_is_on(tr))
		return;

	tracer_tracing_on(tr);
}

static void
ftrace_traceoff(unsigned long ip, unsigned long parent_ip,
		struct trace_array *tr, struct ftrace_probe_ops *ops,
		void *data)
{
	if (!tracer_tracing_is_on(tr))
		return;

	tracer_tracing_off(tr);
}

#ifdef CONFIG_UNWINDER_ORC
/*
 * Skip 3:
 *
 *   function_trace_probe_call()
 *   ftrace_ops_assist_func()
 *   ftrace_call()
 */
#define FTRACE_STACK_SKIP 3
#else
/*
 * Skip 5:
 *
 *   __trace_stack()
 *   ftrace_stacktrace()
 *   function_trace_probe_call()
 *   ftrace_ops_assist_func()
 *   ftrace_call()
 */
#define FTRACE_STACK_SKIP 5
#endif

static __always_inline void trace_stack(struct trace_array *tr)
{
	unsigned int trace_ctx;

	trace_ctx = tracing_gen_ctx();

	__trace_stack(tr, trace_ctx, FTRACE_STACK_SKIP);
}

static void
ftrace_stacktrace(unsigned long ip, unsigned long parent_ip,
		  struct trace_array *tr, struct ftrace_probe_ops *ops,
		  void *data)
{
	trace_stack(tr);
}

static void
ftrace_stacktrace_count(unsigned long ip, unsigned long parent_ip,
			struct trace_array *tr, struct ftrace_probe_ops *ops,
			void *data)
{
	struct ftrace_func_mapper *mapper = data;
	long *count;
	long old_count;
	long new_count;

	if (!tracing_is_on())
		return;

	/* unlimited? */
	if (!mapper) {
		trace_stack(tr);
		return;
	}

	count = (long *)ftrace_func_mapper_find_ip(mapper, ip);

	/*
	 * Stack traces should only execute the number of times the
	 * user specified in the counter.
	 */
	do {
		old_count = *count;

		if (!old_count)
			return;

		new_count = old_count - 1;
		new_count = cmpxchg(count, old_count, new_count);
		if (new_count == old_count)
			trace_stack(tr);

		if (!tracing_is_on())
			return;

	} while (new_count != old_count);
}

static int update_count(struct ftrace_probe_ops *ops, unsigned long ip,
			void *data)
{
	struct ftrace_func_mapper *mapper = data;
	long *count = NULL;

	if (mapper)
		count = (long *)ftrace_func_mapper_find_ip(mapper, ip);

	if (count) {
		if (*count <= 0)
			return 0;
		(*count)--;
	}

	return 1;
}

static void
ftrace_dump_probe(unsigned long ip, unsigned long parent_ip,
		  struct trace_array *tr, struct ftrace_probe_ops *ops,
		  void *data)
{
	if (update_count(ops, ip, data))
		ftrace_dump(DUMP_ALL);
}

/* Only dump the current CPU buffer. */
static void
ftrace_cpudump_probe(unsigned long ip, unsigned long parent_ip,
		     struct trace_array *tr, struct ftrace_probe_ops *ops,
		     void *data)
{
	if (update_count(ops, ip, data))
		ftrace_dump(DUMP_ORIG);
}

static int
ftrace_probe_print(const char *name, struct seq_file *m,
		   unsigned long ip, struct ftrace_probe_ops *ops,
		   void *data)
{
	struct ftrace_func_mapper *mapper = data;
	long *count = NULL;

	seq_printf(m, "%ps:%s", (void *)ip, name);

	if (mapper)
		count = (long *)ftrace_func_mapper_find_ip(mapper, ip);

	if (count)
		seq_printf(m, ":count=%ld\n", *count);
	else
		seq_puts(m, ":unlimited\n");

	return 0;
}

static int
ftrace_traceon_print(struct seq_file *m, unsigned long ip,
		     struct ftrace_probe_ops *ops,
		     void *data)
{
	return ftrace_probe_print("traceon", m, ip, ops, data);
}

static int
ftrace_traceoff_print(struct seq_file *m, unsigned long ip,
			 struct ftrace_probe_ops *ops, void *data)
{
	return ftrace_probe_print("traceoff", m, ip, ops, data);
}

static int
ftrace_stacktrace_print(struct seq_file *m, unsigned long ip,
			struct ftrace_probe_ops *ops, void *data)
{
	return ftrace_probe_print("stacktrace", m, ip, ops, data);
}

static int
ftrace_dump_print(struct seq_file *m, unsigned long ip,
			struct ftrace_probe_ops *ops, void *data)
{
	return ftrace_probe_print("dump", m, ip, ops, data);
}

static int
ftrace_cpudump_print(struct seq_file *m, unsigned long ip,
			struct ftrace_probe_ops *ops, void *data)
{
	return ftrace_probe_print("cpudump", m, ip, ops, data);
}


static int
ftrace_count_init(struct ftrace_probe_ops *ops, struct trace_array *tr,
		  unsigned long ip, void *init_data, void **data)
{
	struct ftrace_func_mapper *mapper = *data;

	if (!mapper) {
		mapper = allocate_ftrace_func_mapper();
		if (!mapper)
			return -ENOMEM;
		*data = mapper;
	}

	return ftrace_func_mapper_add_ip(mapper, ip, init_data);
}

static void
ftrace_count_free(struct ftrace_probe_ops *ops, struct trace_array *tr,
		  unsigned long ip, void *data)
{
	struct ftrace_func_mapper *mapper = data;

	if (!ip) {
		free_ftrace_func_mapper(mapper, NULL);
		return;
	}

	ftrace_func_mapper_remove_ip(mapper, ip);
}

static struct ftrace_probe_ops traceon_count_probe_ops = {
	.func			= ftrace_traceon_count,
	.print			= ftrace_traceon_print,
	.init			= ftrace_count_init,
	.free			= ftrace_count_free,
};

static struct ftrace_probe_ops traceoff_count_probe_ops = {
	.func			= ftrace_traceoff_count,
	.print			= ftrace_traceoff_print,
	.init			= ftrace_count_init,
	.free			= ftrace_count_free,
};

static struct ftrace_probe_ops stacktrace_count_probe_ops = {
	.func			= ftrace_stacktrace_count,
	.print			= ftrace_stacktrace_print,
	.init			= ftrace_count_init,
	.free			= ftrace_count_free,
};

static struct ftrace_probe_ops dump_probe_ops = {
	.func			= ftrace_dump_probe,
	.print			= ftrace_dump_print,
	.init			= ftrace_count_init,
	.free			= ftrace_count_free,
};

static struct ftrace_probe_ops cpudump_probe_ops = {
	.func			= ftrace_cpudump_probe,
	.print			= ftrace_cpudump_print,
};

static struct ftrace_probe_ops traceon_probe_ops = {
	.func			= ftrace_traceon,
	.print			= ftrace_traceon_print,
};

static struct ftrace_probe_ops traceoff_probe_ops = {
	.func			= ftrace_traceoff,
	.print			= ftrace_traceoff_print,
};

static struct ftrace_probe_ops stacktrace_probe_ops = {
	.func			= ftrace_stacktrace,
	.print			= ftrace_stacktrace_print,
};

static int
ftrace_trace_probe_callback(struct trace_array *tr,
			    struct ftrace_probe_ops *ops,
			    struct ftrace_hash *hash, char *glob,
			    char *cmd, char *param, int enable)
{
	void *count = (void *)-1;
	char *number;
	int ret;

	/* hash funcs only work with set_ftrace_filter */
	if (!enable)
		return -EINVAL;

	if (glob[0] == '!')
		return unregister_ftrace_function_probe_func(glob+1, tr, ops);

	if (!param)
		goto out_reg;

	number = strsep(&param, ":");

	if (!strlen(number))
		goto out_reg;

	/*
	 * We use the callback data field (which is a pointer)
	 * as our counter.
	 */
	ret = kstrtoul(number, 0, (unsigned long *)&count);
	if (ret)
		return ret;

 out_reg:
	ret = register_ftrace_function_probe(glob, tr, ops, count);

	return ret < 0 ? ret : 0;
}

static int
ftrace_trace_onoff_callback(struct trace_array *tr, struct ftrace_hash *hash,
			    char *glob, char *cmd, char *param, int enable)
{
	struct ftrace_probe_ops *ops;

	if (!tr)
		return -ENODEV;

	/* we register both traceon and traceoff to this callback */
	if (strcmp(cmd, "traceon") == 0)
		ops = param ? &traceon_count_probe_ops : &traceon_probe_ops;
	else
		ops = param ? &traceoff_count_probe_ops : &traceoff_probe_ops;

	return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
					   param, enable);
}

static int
ftrace_stacktrace_callback(struct trace_array *tr, struct ftrace_hash *hash,
			   char *glob, char *cmd, char *param, int enable)
{
	struct ftrace_probe_ops *ops;

	if (!tr)
		return -ENODEV;

	ops = param ? &stacktrace_count_probe_ops : &stacktrace_probe_ops;

	return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
					   param, enable);
}

static int
ftrace_dump_callback(struct trace_array *tr, struct ftrace_hash *hash,
			   char *glob, char *cmd, char *param, int enable)
{
	struct ftrace_probe_ops *ops;

	if (!tr)
		return -ENODEV;

	ops = &dump_probe_ops;

	/* Only dump once. */
	return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
					   "1", enable);
}

static int
ftrace_cpudump_callback(struct trace_array *tr, struct ftrace_hash *hash,
			   char *glob, char *cmd, char *param, int enable)
{
	struct ftrace_probe_ops *ops;

	if (!tr)
		return -ENODEV;

	ops = &cpudump_probe_ops;

	/* Only dump once. */
	return ftrace_trace_probe_callback(tr, ops, hash, glob, cmd,
					   "1", enable);
}

static struct ftrace_func_command ftrace_traceon_cmd = {
	.name			= "traceon",
	.func			= ftrace_trace_onoff_callback,
};

static struct ftrace_func_command ftrace_traceoff_cmd = {
	.name			= "traceoff",
	.func			= ftrace_trace_onoff_callback,
};

static struct ftrace_func_command ftrace_stacktrace_cmd = {
	.name			= "stacktrace",
	.func			= ftrace_stacktrace_callback,
};

static struct ftrace_func_command ftrace_dump_cmd = {
	.name			= "dump",
	.func			= ftrace_dump_callback,
};

static struct ftrace_func_command ftrace_cpudump_cmd = {
	.name			= "cpudump",
	.func			= ftrace_cpudump_callback,
};

static int __init init_func_cmd_traceon(void)
{
	int ret;

	ret = register_ftrace_command(&ftrace_traceoff_cmd);
	if (ret)
		return ret;

	ret = register_ftrace_command(&ftrace_traceon_cmd);
	if (ret)
		goto out_free_traceoff;

	ret = register_ftrace_command(&ftrace_stacktrace_cmd);
	if (ret)
		goto out_free_traceon;

	ret = register_ftrace_command(&ftrace_dump_cmd);
	if (ret)
		goto out_free_stacktrace;

	ret = register_ftrace_command(&ftrace_cpudump_cmd);
	if (ret)
		goto out_free_dump;

	return 0;

 out_free_dump:
	unregister_ftrace_command(&ftrace_dump_cmd);
 out_free_stacktrace:
	unregister_ftrace_command(&ftrace_stacktrace_cmd);
 out_free_traceon:
	unregister_ftrace_command(&ftrace_traceon_cmd);
 out_free_traceoff:
	unregister_ftrace_command(&ftrace_traceoff_cmd);

	return ret;
}
#else
static inline int init_func_cmd_traceon(void)
{
	return 0;
}
#endif /* CONFIG_DYNAMIC_FTRACE */

__init int init_function_trace(void)
{
	init_func_cmd_traceon();
	return register_tracer(&function_trace);
}