linux/kernel/trace/ring_buffer.c
Steven Rostedt 78d904b46a ring-buffer: add NMI protection for spinlocks
Impact: prevent deadlock in NMI

The ring buffers are not yet totally lockless with writing to
the buffer. When a writer crosses a page, it grabs a per cpu spinlock
to protect against a reader. The spinlocks taken by a writer are not
to protect against other writers, since a writer can only write to
its own per cpu buffer. The spinlocks protect against readers that
can touch any cpu buffer. The writers are made to be reentrant
with the spinlocks disabling interrupts.

The problem arises when an NMI writes to the buffer, and that write
crosses a page boundary. If it grabs a spinlock, it can be racing
with another writer (since disabling interrupts does not protect
against NMIs) or with a reader on the same CPU. Luckily, most of the
users are not reentrant and protects against this issue. But if a
user of the ring buffer becomes reentrant (which is what the ring
buffers do allow), if the NMI also writes to the ring buffer then
we risk the chance of a deadlock.

This patch moves the ftrace_nmi_enter called by nmi_enter() to the
ring buffer code. It replaces the current ftrace_nmi_enter that is
used by arch specific code to arch_ftrace_nmi_enter and updates
the Kconfig to handle it.

When an NMI is called, it will set a per cpu variable in the ring buffer
code and will clear it when the NMI exits. If a write to the ring buffer
crosses page boundaries inside an NMI, a trylock is used on the spin
lock instead. If the spinlock fails to be acquired, then the entry
is discarded.

This bug appeared in the ftrace work in the RT tree, where event tracing
is reentrant. This workaround solved the deadlocks that appeared there.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
2009-02-07 20:00:17 -05:00

2586 lines
63 KiB
C

/*
* Generic ring buffer
*
* Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
*/
#include <linux/ring_buffer.h>
#include <linux/ftrace_irq.h>
#include <linux/spinlock.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/mutex.h>
#include <linux/sched.h> /* used for sched_clock() (for now) */
#include <linux/init.h>
#include <linux/hash.h>
#include <linux/list.h>
#include <linux/fs.h>
#include "trace.h"
/*
* Since the write to the buffer is still not fully lockless,
* we must be careful with NMIs. The locks in the writers
* are taken when a write crosses to a new page. The locks
* protect against races with the readers (this will soon
* be fixed with a lockless solution).
*
* Because we can not protect against NMIs, and we want to
* keep traces reentrant, we need to manage what happens
* when we are in an NMI.
*/
static DEFINE_PER_CPU(int, rb_in_nmi);
void ftrace_nmi_enter(void)
{
__get_cpu_var(rb_in_nmi)++;
/* call arch specific handler too */
arch_ftrace_nmi_enter();
}
void ftrace_nmi_exit(void)
{
arch_ftrace_nmi_exit();
__get_cpu_var(rb_in_nmi)--;
/* NMIs are not recursive */
WARN_ON_ONCE(__get_cpu_var(rb_in_nmi));
}
/*
* A fast way to enable or disable all ring buffers is to
* call tracing_on or tracing_off. Turning off the ring buffers
* prevents all ring buffers from being recorded to.
* Turning this switch on, makes it OK to write to the
* ring buffer, if the ring buffer is enabled itself.
*
* There's three layers that must be on in order to write
* to the ring buffer.
*
* 1) This global flag must be set.
* 2) The ring buffer must be enabled for recording.
* 3) The per cpu buffer must be enabled for recording.
*
* In case of an anomaly, this global flag has a bit set that
* will permantly disable all ring buffers.
*/
/*
* Global flag to disable all recording to ring buffers
* This has two bits: ON, DISABLED
*
* ON DISABLED
* ---- ----------
* 0 0 : ring buffers are off
* 1 0 : ring buffers are on
* X 1 : ring buffers are permanently disabled
*/
enum {
RB_BUFFERS_ON_BIT = 0,
RB_BUFFERS_DISABLED_BIT = 1,
};
enum {
RB_BUFFERS_ON = 1 << RB_BUFFERS_ON_BIT,
RB_BUFFERS_DISABLED = 1 << RB_BUFFERS_DISABLED_BIT,
};
static long ring_buffer_flags __read_mostly = RB_BUFFERS_ON;
/**
* tracing_on - enable all tracing buffers
*
* This function enables all tracing buffers that may have been
* disabled with tracing_off.
*/
void tracing_on(void)
{
set_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_on);
/**
* tracing_off - turn off all tracing buffers
*
* This function stops all tracing buffers from recording data.
* It does not disable any overhead the tracers themselves may
* be causing. This function simply causes all recording to
* the ring buffers to fail.
*/
void tracing_off(void)
{
clear_bit(RB_BUFFERS_ON_BIT, &ring_buffer_flags);
}
EXPORT_SYMBOL_GPL(tracing_off);
/**
* tracing_off_permanent - permanently disable ring buffers
*
* This function, once called, will disable all ring buffers
* permanenty.
*/
void tracing_off_permanent(void)
{
set_bit(RB_BUFFERS_DISABLED_BIT, &ring_buffer_flags);
}
#include "trace.h"
/* Up this if you want to test the TIME_EXTENTS and normalization */
#define DEBUG_SHIFT 0
/* FIXME!!! */
u64 ring_buffer_time_stamp(int cpu)
{
u64 time;
preempt_disable_notrace();
/* shift to debug/test normalization and TIME_EXTENTS */
time = sched_clock() << DEBUG_SHIFT;
preempt_enable_no_resched_notrace();
return time;
}
EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
{
/* Just stupid testing the normalize function and deltas */
*ts >>= DEBUG_SHIFT;
}
EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
#define RB_EVNT_HDR_SIZE (sizeof(struct ring_buffer_event))
#define RB_ALIGNMENT 4U
#define RB_MAX_SMALL_DATA 28
enum {
RB_LEN_TIME_EXTEND = 8,
RB_LEN_TIME_STAMP = 16,
};
/* inline for ring buffer fast paths */
static unsigned
rb_event_length(struct ring_buffer_event *event)
{
unsigned length;
switch (event->type) {
case RINGBUF_TYPE_PADDING:
/* undefined */
return -1;
case RINGBUF_TYPE_TIME_EXTEND:
return RB_LEN_TIME_EXTEND;
case RINGBUF_TYPE_TIME_STAMP:
return RB_LEN_TIME_STAMP;
case RINGBUF_TYPE_DATA:
if (event->len)
length = event->len * RB_ALIGNMENT;
else
length = event->array[0];
return length + RB_EVNT_HDR_SIZE;
default:
BUG();
}
/* not hit */
return 0;
}
/**
* ring_buffer_event_length - return the length of the event
* @event: the event to get the length of
*/
unsigned ring_buffer_event_length(struct ring_buffer_event *event)
{
unsigned length = rb_event_length(event);
if (event->type != RINGBUF_TYPE_DATA)
return length;
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
length -= sizeof(event->array[0]);
return length;
}
EXPORT_SYMBOL_GPL(ring_buffer_event_length);
/* inline for ring buffer fast paths */
static void *
rb_event_data(struct ring_buffer_event *event)
{
BUG_ON(event->type != RINGBUF_TYPE_DATA);
/* If length is in len field, then array[0] has the data */
if (event->len)
return (void *)&event->array[0];
/* Otherwise length is in array[0] and array[1] has the data */
return (void *)&event->array[1];
}
/**
* ring_buffer_event_data - return the data of the event
* @event: the event to get the data from
*/
void *ring_buffer_event_data(struct ring_buffer_event *event)
{
return rb_event_data(event);
}
EXPORT_SYMBOL_GPL(ring_buffer_event_data);
#define for_each_buffer_cpu(buffer, cpu) \
for_each_cpu(cpu, buffer->cpumask)
#define TS_SHIFT 27
#define TS_MASK ((1ULL << TS_SHIFT) - 1)
#define TS_DELTA_TEST (~TS_MASK)
struct buffer_data_page {
u64 time_stamp; /* page time stamp */
local_t commit; /* write commited index */
unsigned char data[]; /* data of buffer page */
};
struct buffer_page {
local_t write; /* index for next write */
unsigned read; /* index for next read */
struct list_head list; /* list of free pages */
struct buffer_data_page *page; /* Actual data page */
};
static void rb_init_page(struct buffer_data_page *bpage)
{
local_set(&bpage->commit, 0);
}
/*
* Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
* this issue out.
*/
static void free_buffer_page(struct buffer_page *bpage)
{
free_page((unsigned long)bpage->page);
kfree(bpage);
}
/*
* We need to fit the time_stamp delta into 27 bits.
*/
static inline int test_time_stamp(u64 delta)
{
if (delta & TS_DELTA_TEST)
return 1;
return 0;
}
#define BUF_PAGE_SIZE (PAGE_SIZE - offsetof(struct buffer_data_page, data))
/*
* head_page == tail_page && head == tail then buffer is empty.
*/
struct ring_buffer_per_cpu {
int cpu;
struct ring_buffer *buffer;
spinlock_t reader_lock; /* serialize readers */
raw_spinlock_t lock;
struct lock_class_key lock_key;
struct list_head pages;
struct buffer_page *head_page; /* read from head */
struct buffer_page *tail_page; /* write to tail */
struct buffer_page *commit_page; /* commited pages */
struct buffer_page *reader_page;
unsigned long overrun;
unsigned long entries;
u64 write_stamp;
u64 read_stamp;
atomic_t record_disabled;
};
struct ring_buffer {
unsigned pages;
unsigned flags;
int cpus;
cpumask_var_t cpumask;
atomic_t record_disabled;
struct mutex mutex;
struct ring_buffer_per_cpu **buffers;
};
struct ring_buffer_iter {
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long head;
struct buffer_page *head_page;
u64 read_stamp;
};
/* buffer may be either ring_buffer or ring_buffer_per_cpu */
#define RB_WARN_ON(buffer, cond) \
({ \
int _____ret = unlikely(cond); \
if (_____ret) { \
atomic_inc(&buffer->record_disabled); \
WARN_ON(1); \
} \
_____ret; \
})
/**
* check_pages - integrity check of buffer pages
* @cpu_buffer: CPU buffer with pages to test
*
* As a safty measure we check to make sure the data pages have not
* been corrupted.
*/
static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = &cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
return -1;
if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
return -1;
list_for_each_entry_safe(bpage, tmp, head, list) {
if (RB_WARN_ON(cpu_buffer,
bpage->list.next->prev != &bpage->list))
return -1;
if (RB_WARN_ON(cpu_buffer,
bpage->list.prev->next != &bpage->list))
return -1;
}
return 0;
}
static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
unsigned nr_pages)
{
struct list_head *head = &cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
unsigned long addr;
LIST_HEAD(pages);
unsigned i;
for (i = 0; i < nr_pages; i++) {
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
if (!bpage)
goto free_pages;
list_add(&bpage->list, &pages);
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto free_pages;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
}
list_splice(&pages, head);
rb_check_pages(cpu_buffer);
return 0;
free_pages:
list_for_each_entry_safe(bpage, tmp, &pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
return -ENOMEM;
}
static struct ring_buffer_per_cpu *
rb_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct buffer_page *bpage;
unsigned long addr;
int ret;
cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!cpu_buffer)
return NULL;
cpu_buffer->cpu = cpu;
cpu_buffer->buffer = buffer;
spin_lock_init(&cpu_buffer->reader_lock);
cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
INIT_LIST_HEAD(&cpu_buffer->pages);
bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!bpage)
goto fail_free_buffer;
cpu_buffer->reader_page = bpage;
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto fail_free_reader;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
ret = rb_allocate_pages(cpu_buffer, buffer->pages);
if (ret < 0)
goto fail_free_reader;
cpu_buffer->head_page
= list_entry(cpu_buffer->pages.next, struct buffer_page, list);
cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
return cpu_buffer;
fail_free_reader:
free_buffer_page(cpu_buffer->reader_page);
fail_free_buffer:
kfree(cpu_buffer);
return NULL;
}
static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
{
struct list_head *head = &cpu_buffer->pages;
struct buffer_page *bpage, *tmp;
list_del_init(&cpu_buffer->reader_page->list);
free_buffer_page(cpu_buffer->reader_page);
list_for_each_entry_safe(bpage, tmp, head, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
kfree(cpu_buffer);
}
/*
* Causes compile errors if the struct buffer_page gets bigger
* than the struct page.
*/
extern int ring_buffer_page_too_big(void);
/**
* ring_buffer_alloc - allocate a new ring_buffer
* @size: the size in bytes per cpu that is needed.
* @flags: attributes to set for the ring buffer.
*
* Currently the only flag that is available is the RB_FL_OVERWRITE
* flag. This flag means that the buffer will overwrite old data
* when the buffer wraps. If this flag is not set, the buffer will
* drop data when the tail hits the head.
*/
struct ring_buffer *ring_buffer_alloc(unsigned long size, unsigned flags)
{
struct ring_buffer *buffer;
int bsize;
int cpu;
/* Paranoid! Optimizes out when all is well */
if (sizeof(struct buffer_page) > sizeof(struct page))
ring_buffer_page_too_big();
/* keep it in its own cache line */
buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
GFP_KERNEL);
if (!buffer)
return NULL;
if (!alloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
goto fail_free_buffer;
buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
buffer->flags = flags;
/* need at least two pages */
if (buffer->pages == 1)
buffer->pages++;
cpumask_copy(buffer->cpumask, cpu_possible_mask);
buffer->cpus = nr_cpu_ids;
bsize = sizeof(void *) * nr_cpu_ids;
buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
GFP_KERNEL);
if (!buffer->buffers)
goto fail_free_cpumask;
for_each_buffer_cpu(buffer, cpu) {
buffer->buffers[cpu] =
rb_allocate_cpu_buffer(buffer, cpu);
if (!buffer->buffers[cpu])
goto fail_free_buffers;
}
mutex_init(&buffer->mutex);
return buffer;
fail_free_buffers:
for_each_buffer_cpu(buffer, cpu) {
if (buffer->buffers[cpu])
rb_free_cpu_buffer(buffer->buffers[cpu]);
}
kfree(buffer->buffers);
fail_free_cpumask:
free_cpumask_var(buffer->cpumask);
fail_free_buffer:
kfree(buffer);
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_alloc);
/**
* ring_buffer_free - free a ring buffer.
* @buffer: the buffer to free.
*/
void
ring_buffer_free(struct ring_buffer *buffer)
{
int cpu;
for_each_buffer_cpu(buffer, cpu)
rb_free_cpu_buffer(buffer->buffers[cpu]);
free_cpumask_var(buffer->cpumask);
kfree(buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_free);
static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
static void
rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
{
struct buffer_page *bpage;
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
for (i = 0; i < nr_pages; i++) {
if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
return;
p = cpu_buffer->pages.next;
bpage = list_entry(p, struct buffer_page, list);
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
if (RB_WARN_ON(cpu_buffer, list_empty(&cpu_buffer->pages)))
return;
rb_reset_cpu(cpu_buffer);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
static void
rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
struct list_head *pages, unsigned nr_pages)
{
struct buffer_page *bpage;
struct list_head *p;
unsigned i;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
for (i = 0; i < nr_pages; i++) {
if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
return;
p = pages->next;
bpage = list_entry(p, struct buffer_page, list);
list_del_init(&bpage->list);
list_add_tail(&bpage->list, &cpu_buffer->pages);
}
rb_reset_cpu(cpu_buffer);
rb_check_pages(cpu_buffer);
atomic_dec(&cpu_buffer->record_disabled);
}
/**
* ring_buffer_resize - resize the ring buffer
* @buffer: the buffer to resize.
* @size: the new size.
*
* The tracer is responsible for making sure that the buffer is
* not being used while changing the size.
* Note: We may be able to change the above requirement by using
* RCU synchronizations.
*
* Minimum size is 2 * BUF_PAGE_SIZE.
*
* Returns -1 on failure.
*/
int ring_buffer_resize(struct ring_buffer *buffer, unsigned long size)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned nr_pages, rm_pages, new_pages;
struct buffer_page *bpage, *tmp;
unsigned long buffer_size;
unsigned long addr;
LIST_HEAD(pages);
int i, cpu;
/*
* Always succeed at resizing a non-existent buffer:
*/
if (!buffer)
return size;
size = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
size *= BUF_PAGE_SIZE;
buffer_size = buffer->pages * BUF_PAGE_SIZE;
/* we need a minimum of two pages */
if (size < BUF_PAGE_SIZE * 2)
size = BUF_PAGE_SIZE * 2;
if (size == buffer_size)
return size;
mutex_lock(&buffer->mutex);
nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
if (size < buffer_size) {
/* easy case, just free pages */
if (RB_WARN_ON(buffer, nr_pages >= buffer->pages)) {
mutex_unlock(&buffer->mutex);
return -1;
}
rm_pages = buffer->pages - nr_pages;
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
rb_remove_pages(cpu_buffer, rm_pages);
}
goto out;
}
/*
* This is a bit more difficult. We only want to add pages
* when we can allocate enough for all CPUs. We do this
* by allocating all the pages and storing them on a local
* link list. If we succeed in our allocation, then we
* add these pages to the cpu_buffers. Otherwise we just free
* them all and return -ENOMEM;
*/
if (RB_WARN_ON(buffer, nr_pages <= buffer->pages)) {
mutex_unlock(&buffer->mutex);
return -1;
}
new_pages = nr_pages - buffer->pages;
for_each_buffer_cpu(buffer, cpu) {
for (i = 0; i < new_pages; i++) {
bpage = kzalloc_node(ALIGN(sizeof(*bpage),
cache_line_size()),
GFP_KERNEL, cpu_to_node(cpu));
if (!bpage)
goto free_pages;
list_add(&bpage->list, &pages);
addr = __get_free_page(GFP_KERNEL);
if (!addr)
goto free_pages;
bpage->page = (void *)addr;
rb_init_page(bpage->page);
}
}
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
rb_insert_pages(cpu_buffer, &pages, new_pages);
}
if (RB_WARN_ON(buffer, !list_empty(&pages))) {
mutex_unlock(&buffer->mutex);
return -1;
}
out:
buffer->pages = nr_pages;
mutex_unlock(&buffer->mutex);
return size;
free_pages:
list_for_each_entry_safe(bpage, tmp, &pages, list) {
list_del_init(&bpage->list);
free_buffer_page(bpage);
}
mutex_unlock(&buffer->mutex);
return -ENOMEM;
}
EXPORT_SYMBOL_GPL(ring_buffer_resize);
static inline int rb_null_event(struct ring_buffer_event *event)
{
return event->type == RINGBUF_TYPE_PADDING;
}
static inline void *
__rb_data_page_index(struct buffer_data_page *bpage, unsigned index)
{
return bpage->data + index;
}
static inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
{
return bpage->page->data + index;
}
static inline struct ring_buffer_event *
rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
{
return __rb_page_index(cpu_buffer->reader_page,
cpu_buffer->reader_page->read);
}
static inline struct ring_buffer_event *
rb_head_event(struct ring_buffer_per_cpu *cpu_buffer)
{
return __rb_page_index(cpu_buffer->head_page,
cpu_buffer->head_page->read);
}
static inline struct ring_buffer_event *
rb_iter_head_event(struct ring_buffer_iter *iter)
{
return __rb_page_index(iter->head_page, iter->head);
}
static inline unsigned rb_page_write(struct buffer_page *bpage)
{
return local_read(&bpage->write);
}
static inline unsigned rb_page_commit(struct buffer_page *bpage)
{
return local_read(&bpage->page->commit);
}
/* Size is determined by what has been commited */
static inline unsigned rb_page_size(struct buffer_page *bpage)
{
return rb_page_commit(bpage);
}
static inline unsigned
rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
{
return rb_page_commit(cpu_buffer->commit_page);
}
static inline unsigned rb_head_size(struct ring_buffer_per_cpu *cpu_buffer)
{
return rb_page_commit(cpu_buffer->head_page);
}
/*
* When the tail hits the head and the buffer is in overwrite mode,
* the head jumps to the next page and all content on the previous
* page is discarded. But before doing so, we update the overrun
* variable of the buffer.
*/
static void rb_update_overflow(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_event *event;
unsigned long head;
for (head = 0; head < rb_head_size(cpu_buffer);
head += rb_event_length(event)) {
event = __rb_page_index(cpu_buffer->head_page, head);
if (RB_WARN_ON(cpu_buffer, rb_null_event(event)))
return;
/* Only count data entries */
if (event->type != RINGBUF_TYPE_DATA)
continue;
cpu_buffer->overrun++;
cpu_buffer->entries--;
}
}
static inline void rb_inc_page(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_page **bpage)
{
struct list_head *p = (*bpage)->list.next;
if (p == &cpu_buffer->pages)
p = p->next;
*bpage = list_entry(p, struct buffer_page, list);
}
static inline unsigned
rb_event_index(struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
return (addr & ~PAGE_MASK) - (PAGE_SIZE - BUF_PAGE_SIZE);
}
static int
rb_is_commit(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
unsigned long index;
index = rb_event_index(event);
addr &= PAGE_MASK;
return cpu_buffer->commit_page->page == (void *)addr &&
rb_commit_index(cpu_buffer) == index;
}
static void
rb_set_commit_event(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
unsigned long addr = (unsigned long)event;
unsigned long index;
index = rb_event_index(event);
addr &= PAGE_MASK;
while (cpu_buffer->commit_page->page != (void *)addr) {
if (RB_WARN_ON(cpu_buffer,
cpu_buffer->commit_page == cpu_buffer->tail_page))
return;
cpu_buffer->commit_page->page->commit =
cpu_buffer->commit_page->write;
rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
cpu_buffer->write_stamp =
cpu_buffer->commit_page->page->time_stamp;
}
/* Now set the commit to the event's index */
local_set(&cpu_buffer->commit_page->page->commit, index);
}
static void
rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
{
/*
* We only race with interrupts and NMIs on this CPU.
* If we own the commit event, then we can commit
* all others that interrupted us, since the interruptions
* are in stack format (they finish before they come
* back to us). This allows us to do a simple loop to
* assign the commit to the tail.
*/
again:
while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
cpu_buffer->commit_page->page->commit =
cpu_buffer->commit_page->write;
rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
cpu_buffer->write_stamp =
cpu_buffer->commit_page->page->time_stamp;
/* add barrier to keep gcc from optimizing too much */
barrier();
}
while (rb_commit_index(cpu_buffer) !=
rb_page_write(cpu_buffer->commit_page)) {
cpu_buffer->commit_page->page->commit =
cpu_buffer->commit_page->write;
barrier();
}
/* again, keep gcc from optimizing */
barrier();
/*
* If an interrupt came in just after the first while loop
* and pushed the tail page forward, we will be left with
* a dangling commit that will never go forward.
*/
if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
goto again;
}
static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
cpu_buffer->read_stamp = cpu_buffer->reader_page->page->time_stamp;
cpu_buffer->reader_page->read = 0;
}
static void rb_inc_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/*
* The iterator could be on the reader page (it starts there).
* But the head could have moved, since the reader was
* found. Check for this case and assign the iterator
* to the head page instead of next.
*/
if (iter->head_page == cpu_buffer->reader_page)
iter->head_page = cpu_buffer->head_page;
else
rb_inc_page(cpu_buffer, &iter->head_page);
iter->read_stamp = iter->head_page->page->time_stamp;
iter->head = 0;
}
/**
* ring_buffer_update_event - update event type and data
* @event: the even to update
* @type: the type of event
* @length: the size of the event field in the ring buffer
*
* Update the type and data fields of the event. The length
* is the actual size that is written to the ring buffer,
* and with this, we can determine what to place into the
* data field.
*/
static void
rb_update_event(struct ring_buffer_event *event,
unsigned type, unsigned length)
{
event->type = type;
switch (type) {
case RINGBUF_TYPE_PADDING:
break;
case RINGBUF_TYPE_TIME_EXTEND:
event->len = DIV_ROUND_UP(RB_LEN_TIME_EXTEND, RB_ALIGNMENT);
break;
case RINGBUF_TYPE_TIME_STAMP:
event->len = DIV_ROUND_UP(RB_LEN_TIME_STAMP, RB_ALIGNMENT);
break;
case RINGBUF_TYPE_DATA:
length -= RB_EVNT_HDR_SIZE;
if (length > RB_MAX_SMALL_DATA) {
event->len = 0;
event->array[0] = length;
} else
event->len = DIV_ROUND_UP(length, RB_ALIGNMENT);
break;
default:
BUG();
}
}
static unsigned rb_calculate_event_length(unsigned length)
{
struct ring_buffer_event event; /* Used only for sizeof array */
/* zero length can cause confusions */
if (!length)
length = 1;
if (length > RB_MAX_SMALL_DATA)
length += sizeof(event.array[0]);
length += RB_EVNT_HDR_SIZE;
length = ALIGN(length, RB_ALIGNMENT);
return length;
}
static struct ring_buffer_event *
__rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
unsigned type, unsigned long length, u64 *ts)
{
struct buffer_page *tail_page, *head_page, *reader_page, *commit_page;
unsigned long tail, write;
struct ring_buffer *buffer = cpu_buffer->buffer;
struct ring_buffer_event *event;
unsigned long flags;
bool lock_taken = false;
commit_page = cpu_buffer->commit_page;
/* we just need to protect against interrupts */
barrier();
tail_page = cpu_buffer->tail_page;
write = local_add_return(length, &tail_page->write);
tail = write - length;
/* See if we shot pass the end of this buffer page */
if (write > BUF_PAGE_SIZE) {
struct buffer_page *next_page = tail_page;
local_irq_save(flags);
/*
* NMIs can happen after we take the lock.
* If we are in an NMI, only take the lock
* if it is not already taken. Otherwise
* simply fail.
*/
if (unlikely(__get_cpu_var(rb_in_nmi))) {
if (!__raw_spin_trylock(&cpu_buffer->lock))
goto out_unlock;
} else
__raw_spin_lock(&cpu_buffer->lock);
lock_taken = true;
rb_inc_page(cpu_buffer, &next_page);
head_page = cpu_buffer->head_page;
reader_page = cpu_buffer->reader_page;
/* we grabbed the lock before incrementing */
if (RB_WARN_ON(cpu_buffer, next_page == reader_page))
goto out_unlock;
/*
* If for some reason, we had an interrupt storm that made
* it all the way around the buffer, bail, and warn
* about it.
*/
if (unlikely(next_page == commit_page)) {
WARN_ON_ONCE(1);
goto out_unlock;
}
if (next_page == head_page) {
if (!(buffer->flags & RB_FL_OVERWRITE))
goto out_unlock;
/* tail_page has not moved yet? */
if (tail_page == cpu_buffer->tail_page) {
/* count overflows */
rb_update_overflow(cpu_buffer);
rb_inc_page(cpu_buffer, &head_page);
cpu_buffer->head_page = head_page;
cpu_buffer->head_page->read = 0;
}
}
/*
* If the tail page is still the same as what we think
* it is, then it is up to us to update the tail
* pointer.
*/
if (tail_page == cpu_buffer->tail_page) {
local_set(&next_page->write, 0);
local_set(&next_page->page->commit, 0);
cpu_buffer->tail_page = next_page;
/* reread the time stamp */
*ts = ring_buffer_time_stamp(cpu_buffer->cpu);
cpu_buffer->tail_page->page->time_stamp = *ts;
}
/*
* The actual tail page has moved forward.
*/
if (tail < BUF_PAGE_SIZE) {
/* Mark the rest of the page with padding */
event = __rb_page_index(tail_page, tail);
event->type = RINGBUF_TYPE_PADDING;
}
if (tail <= BUF_PAGE_SIZE)
/* Set the write back to the previous setting */
local_set(&tail_page->write, tail);
/*
* If this was a commit entry that failed,
* increment that too
*/
if (tail_page == cpu_buffer->commit_page &&
tail == rb_commit_index(cpu_buffer)) {
rb_set_commit_to_write(cpu_buffer);
}
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
/* fail and let the caller try again */
return ERR_PTR(-EAGAIN);
}
/* We reserved something on the buffer */
if (RB_WARN_ON(cpu_buffer, write > BUF_PAGE_SIZE))
return NULL;
event = __rb_page_index(tail_page, tail);
rb_update_event(event, type, length);
/*
* If this is a commit and the tail is zero, then update
* this page's time stamp.
*/
if (!tail && rb_is_commit(cpu_buffer, event))
cpu_buffer->commit_page->page->time_stamp = *ts;
return event;
out_unlock:
/* reset write */
if (tail <= BUF_PAGE_SIZE)
local_set(&tail_page->write, tail);
if (likely(lock_taken))
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
return NULL;
}
static int
rb_add_time_stamp(struct ring_buffer_per_cpu *cpu_buffer,
u64 *ts, u64 *delta)
{
struct ring_buffer_event *event;
static int once;
int ret;
if (unlikely(*delta > (1ULL << 59) && !once++)) {
printk(KERN_WARNING "Delta way too big! %llu"
" ts=%llu write stamp = %llu\n",
(unsigned long long)*delta,
(unsigned long long)*ts,
(unsigned long long)cpu_buffer->write_stamp);
WARN_ON(1);
}
/*
* The delta is too big, we to add a
* new timestamp.
*/
event = __rb_reserve_next(cpu_buffer,
RINGBUF_TYPE_TIME_EXTEND,
RB_LEN_TIME_EXTEND,
ts);
if (!event)
return -EBUSY;
if (PTR_ERR(event) == -EAGAIN)
return -EAGAIN;
/* Only a commited time event can update the write stamp */
if (rb_is_commit(cpu_buffer, event)) {
/*
* If this is the first on the page, then we need to
* update the page itself, and just put in a zero.
*/
if (rb_event_index(event)) {
event->time_delta = *delta & TS_MASK;
event->array[0] = *delta >> TS_SHIFT;
} else {
cpu_buffer->commit_page->page->time_stamp = *ts;
event->time_delta = 0;
event->array[0] = 0;
}
cpu_buffer->write_stamp = *ts;
/* let the caller know this was the commit */
ret = 1;
} else {
/* Darn, this is just wasted space */
event->time_delta = 0;
event->array[0] = 0;
ret = 0;
}
*delta = 0;
return ret;
}
static struct ring_buffer_event *
rb_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
unsigned type, unsigned long length)
{
struct ring_buffer_event *event;
u64 ts, delta;
int commit = 0;
int nr_loops = 0;
again:
/*
* We allow for interrupts to reenter here and do a trace.
* If one does, it will cause this original code to loop
* back here. Even with heavy interrupts happening, this
* should only happen a few times in a row. If this happens
* 1000 times in a row, there must be either an interrupt
* storm or we have something buggy.
* Bail!
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
return NULL;
ts = ring_buffer_time_stamp(cpu_buffer->cpu);
/*
* Only the first commit can update the timestamp.
* Yes there is a race here. If an interrupt comes in
* just after the conditional and it traces too, then it
* will also check the deltas. More than one timestamp may
* also be made. But only the entry that did the actual
* commit will be something other than zero.
*/
if (cpu_buffer->tail_page == cpu_buffer->commit_page &&
rb_page_write(cpu_buffer->tail_page) ==
rb_commit_index(cpu_buffer)) {
delta = ts - cpu_buffer->write_stamp;
/* make sure this delta is calculated here */
barrier();
/* Did the write stamp get updated already? */
if (unlikely(ts < cpu_buffer->write_stamp))
delta = 0;
if (test_time_stamp(delta)) {
commit = rb_add_time_stamp(cpu_buffer, &ts, &delta);
if (commit == -EBUSY)
return NULL;
if (commit == -EAGAIN)
goto again;
RB_WARN_ON(cpu_buffer, commit < 0);
}
} else
/* Non commits have zero deltas */
delta = 0;
event = __rb_reserve_next(cpu_buffer, type, length, &ts);
if (PTR_ERR(event) == -EAGAIN)
goto again;
if (!event) {
if (unlikely(commit))
/*
* Ouch! We needed a timestamp and it was commited. But
* we didn't get our event reserved.
*/
rb_set_commit_to_write(cpu_buffer);
return NULL;
}
/*
* If the timestamp was commited, make the commit our entry
* now so that we will update it when needed.
*/
if (commit)
rb_set_commit_event(cpu_buffer, event);
else if (!rb_is_commit(cpu_buffer, event))
delta = 0;
event->time_delta = delta;
return event;
}
static DEFINE_PER_CPU(int, rb_need_resched);
/**
* ring_buffer_lock_reserve - reserve a part of the buffer
* @buffer: the ring buffer to reserve from
* @length: the length of the data to reserve (excluding event header)
* @flags: a pointer to save the interrupt flags
*
* Returns a reseverd event on the ring buffer to copy directly to.
* The user of this interface will need to get the body to write into
* and can use the ring_buffer_event_data() interface.
*
* The length is the length of the data needed, not the event length
* which also includes the event header.
*
* Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
* If NULL is returned, then nothing has been allocated or locked.
*/
struct ring_buffer_event *
ring_buffer_lock_reserve(struct ring_buffer *buffer,
unsigned long length,
unsigned long *flags)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int cpu, resched;
if (ring_buffer_flags != RB_BUFFERS_ON)
return NULL;
if (atomic_read(&buffer->record_disabled))
return NULL;
/* If we are tracing schedule, we don't want to recurse */
resched = ftrace_preempt_disable();
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->record_disabled))
goto out;
length = rb_calculate_event_length(length);
if (length > BUF_PAGE_SIZE)
goto out;
event = rb_reserve_next_event(cpu_buffer, RINGBUF_TYPE_DATA, length);
if (!event)
goto out;
/*
* Need to store resched state on this cpu.
* Only the first needs to.
*/
if (preempt_count() == 1)
per_cpu(rb_need_resched, cpu) = resched;
return event;
out:
ftrace_preempt_enable(resched);
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
cpu_buffer->entries++;
/* Only process further if we own the commit */
if (!rb_is_commit(cpu_buffer, event))
return;
cpu_buffer->write_stamp += event->time_delta;
rb_set_commit_to_write(cpu_buffer);
}
/**
* ring_buffer_unlock_commit - commit a reserved
* @buffer: The buffer to commit to
* @event: The event pointer to commit.
* @flags: the interrupt flags received from ring_buffer_lock_reserve.
*
* This commits the data to the ring buffer, and releases any locks held.
*
* Must be paired with ring_buffer_lock_reserve.
*/
int ring_buffer_unlock_commit(struct ring_buffer *buffer,
struct ring_buffer_event *event,
unsigned long flags)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu = raw_smp_processor_id();
cpu_buffer = buffer->buffers[cpu];
rb_commit(cpu_buffer, event);
/*
* Only the last preempt count needs to restore preemption.
*/
if (preempt_count() == 1)
ftrace_preempt_enable(per_cpu(rb_need_resched, cpu));
else
preempt_enable_no_resched_notrace();
return 0;
}
EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
/**
* ring_buffer_write - write data to the buffer without reserving
* @buffer: The ring buffer to write to.
* @length: The length of the data being written (excluding the event header)
* @data: The data to write to the buffer.
*
* This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
* one function. If you already have the data to write to the buffer, it
* may be easier to simply call this function.
*
* Note, like ring_buffer_lock_reserve, the length is the length of the data
* and not the length of the event which would hold the header.
*/
int ring_buffer_write(struct ring_buffer *buffer,
unsigned long length,
void *data)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
unsigned long event_length;
void *body;
int ret = -EBUSY;
int cpu, resched;
if (ring_buffer_flags != RB_BUFFERS_ON)
return -EBUSY;
if (atomic_read(&buffer->record_disabled))
return -EBUSY;
resched = ftrace_preempt_disable();
cpu = raw_smp_processor_id();
if (!cpumask_test_cpu(cpu, buffer->cpumask))
goto out;
cpu_buffer = buffer->buffers[cpu];
if (atomic_read(&cpu_buffer->record_disabled))
goto out;
event_length = rb_calculate_event_length(length);
event = rb_reserve_next_event(cpu_buffer,
RINGBUF_TYPE_DATA, event_length);
if (!event)
goto out;
body = rb_event_data(event);
memcpy(body, data, length);
rb_commit(cpu_buffer, event);
ret = 0;
out:
ftrace_preempt_enable(resched);
return ret;
}
EXPORT_SYMBOL_GPL(ring_buffer_write);
static int rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = cpu_buffer->reader_page;
struct buffer_page *head = cpu_buffer->head_page;
struct buffer_page *commit = cpu_buffer->commit_page;
return reader->read == rb_page_commit(reader) &&
(commit == reader ||
(commit == head &&
head->read == rb_page_commit(commit)));
}
/**
* ring_buffer_record_disable - stop all writes into the buffer
* @buffer: The ring buffer to stop writes to.
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_sched() after this.
*/
void ring_buffer_record_disable(struct ring_buffer *buffer)
{
atomic_inc(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
/**
* ring_buffer_record_enable - enable writes to the buffer
* @buffer: The ring buffer to enable writes
*
* Note, multiple disables will need the same number of enables
* to truely enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable(struct ring_buffer *buffer)
{
atomic_dec(&buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
/**
* ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
* @buffer: The ring buffer to stop writes to.
* @cpu: The CPU buffer to stop
*
* This prevents all writes to the buffer. Any attempt to write
* to the buffer after this will fail and return NULL.
*
* The caller should call synchronize_sched() after this.
*/
void ring_buffer_record_disable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_inc(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
/**
* ring_buffer_record_enable_cpu - enable writes to the buffer
* @buffer: The ring buffer to enable writes
* @cpu: The CPU to enable.
*
* Note, multiple disables will need the same number of enables
* to truely enable the writing (much like preempt_disable).
*/
void ring_buffer_record_enable_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
cpu_buffer = buffer->buffers[cpu];
atomic_dec(&cpu_buffer->record_disabled);
}
EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
/**
* ring_buffer_entries_cpu - get the number of entries in a cpu buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the entries from.
*/
unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
return cpu_buffer->entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
/**
* ring_buffer_overrun_cpu - get the number of overruns in a cpu_buffer
* @buffer: The ring buffer
* @cpu: The per CPU buffer to get the number of overruns from
*/
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 0;
cpu_buffer = buffer->buffers[cpu];
return cpu_buffer->overrun;
}
EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
/**
* ring_buffer_entries - get the number of entries in a buffer
* @buffer: The ring buffer
*
* Returns the total number of entries in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_entries(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long entries = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
entries += cpu_buffer->entries;
}
return entries;
}
EXPORT_SYMBOL_GPL(ring_buffer_entries);
/**
* ring_buffer_overrun_cpu - get the number of overruns in buffer
* @buffer: The ring buffer
*
* Returns the total number of overruns in the ring buffer
* (all CPU entries)
*/
unsigned long ring_buffer_overruns(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
unsigned long overruns = 0;
int cpu;
/* if you care about this being correct, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
overruns += cpu_buffer->overrun;
}
return overruns;
}
EXPORT_SYMBOL_GPL(ring_buffer_overruns);
static void rb_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
/* Iterator usage is expected to have record disabled */
if (list_empty(&cpu_buffer->reader_page->list)) {
iter->head_page = cpu_buffer->head_page;
iter->head = cpu_buffer->head_page->read;
} else {
iter->head_page = cpu_buffer->reader_page;
iter->head = cpu_buffer->reader_page->read;
}
if (iter->head)
iter->read_stamp = cpu_buffer->read_stamp;
else
iter->read_stamp = iter->head_page->page->time_stamp;
}
/**
* ring_buffer_iter_reset - reset an iterator
* @iter: The iterator to reset
*
* Resets the iterator, so that it will start from the beginning
* again.
*/
void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
rb_iter_reset(iter);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
/**
* ring_buffer_iter_empty - check if an iterator has no more to read
* @iter: The iterator to check
*/
int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer;
cpu_buffer = iter->cpu_buffer;
return iter->head_page == cpu_buffer->commit_page &&
iter->head == rb_commit_index(cpu_buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
static void
rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
cpu_buffer->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
return;
case RINGBUF_TYPE_DATA:
cpu_buffer->read_stamp += event->time_delta;
return;
default:
BUG();
}
return;
}
static void
rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
struct ring_buffer_event *event)
{
u64 delta;
switch (event->type) {
case RINGBUF_TYPE_PADDING:
return;
case RINGBUF_TYPE_TIME_EXTEND:
delta = event->array[0];
delta <<= TS_SHIFT;
delta += event->time_delta;
iter->read_stamp += delta;
return;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
return;
case RINGBUF_TYPE_DATA:
iter->read_stamp += event->time_delta;
return;
default:
BUG();
}
return;
}
static struct buffer_page *
rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
{
struct buffer_page *reader = NULL;
unsigned long flags;
int nr_loops = 0;
local_irq_save(flags);
__raw_spin_lock(&cpu_buffer->lock);
again:
/*
* This should normally only loop twice. But because the
* start of the reader inserts an empty page, it causes
* a case where we will loop three times. There should be no
* reason to loop four times (that I know of).
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
reader = NULL;
goto out;
}
reader = cpu_buffer->reader_page;
/* If there's more to read, return this page */
if (cpu_buffer->reader_page->read < rb_page_size(reader))
goto out;
/* Never should we have an index greater than the size */
if (RB_WARN_ON(cpu_buffer,
cpu_buffer->reader_page->read > rb_page_size(reader)))
goto out;
/* check if we caught up to the tail */
reader = NULL;
if (cpu_buffer->commit_page == cpu_buffer->reader_page)
goto out;
/*
* Splice the empty reader page into the list around the head.
* Reset the reader page to size zero.
*/
reader = cpu_buffer->head_page;
cpu_buffer->reader_page->list.next = reader->list.next;
cpu_buffer->reader_page->list.prev = reader->list.prev;
local_set(&cpu_buffer->reader_page->write, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);
/* Make the reader page now replace the head */
reader->list.prev->next = &cpu_buffer->reader_page->list;
reader->list.next->prev = &cpu_buffer->reader_page->list;
/*
* If the tail is on the reader, then we must set the head
* to the inserted page, otherwise we set it one before.
*/
cpu_buffer->head_page = cpu_buffer->reader_page;
if (cpu_buffer->commit_page != reader)
rb_inc_page(cpu_buffer, &cpu_buffer->head_page);
/* Finally update the reader page to the new head */
cpu_buffer->reader_page = reader;
rb_reset_reader_page(cpu_buffer);
goto again;
out:
__raw_spin_unlock(&cpu_buffer->lock);
local_irq_restore(flags);
return reader;
}
static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
{
struct ring_buffer_event *event;
struct buffer_page *reader;
unsigned length;
reader = rb_get_reader_page(cpu_buffer);
/* This function should not be called when buffer is empty */
if (RB_WARN_ON(cpu_buffer, !reader))
return;
event = rb_reader_event(cpu_buffer);
if (event->type == RINGBUF_TYPE_DATA)
cpu_buffer->entries--;
rb_update_read_stamp(cpu_buffer, event);
length = rb_event_length(event);
cpu_buffer->reader_page->read += length;
}
static void rb_advance_iter(struct ring_buffer_iter *iter)
{
struct ring_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
unsigned length;
cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;
/*
* Check if we are at the end of the buffer.
*/
if (iter->head >= rb_page_size(iter->head_page)) {
if (RB_WARN_ON(buffer,
iter->head_page == cpu_buffer->commit_page))
return;
rb_inc_iter(iter);
return;
}
event = rb_iter_head_event(iter);
length = rb_event_length(event);
/*
* This should not be called to advance the header if we are
* at the tail of the buffer.
*/
if (RB_WARN_ON(cpu_buffer,
(iter->head_page == cpu_buffer->commit_page) &&
(iter->head + length > rb_commit_index(cpu_buffer))))
return;
rb_update_iter_read_stamp(iter, event);
iter->head += length;
/* check for end of page padding */
if ((iter->head >= rb_page_size(iter->head_page)) &&
(iter->head_page != cpu_buffer->commit_page))
rb_advance_iter(iter);
}
static struct ring_buffer_event *
rb_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
struct buffer_page *reader;
int nr_loops = 0;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
cpu_buffer = buffer->buffers[cpu];
again:
/*
* We repeat when a timestamp is encountered. It is possible
* to get multiple timestamps from an interrupt entering just
* as one timestamp is about to be written. The max times
* that this can happen is the number of nested interrupts we
* can have. Nesting 10 deep of interrupts is clearly
* an anomaly.
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 10))
return NULL;
reader = rb_get_reader_page(cpu_buffer);
if (!reader)
return NULL;
event = rb_reader_event(cpu_buffer);
switch (event->type) {
case RINGBUF_TYPE_PADDING:
RB_WARN_ON(cpu_buffer, 1);
rb_advance_reader(cpu_buffer);
return NULL;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
rb_advance_reader(cpu_buffer);
goto again;
case RINGBUF_TYPE_DATA:
if (ts) {
*ts = cpu_buffer->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
}
return event;
default:
BUG();
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_peek);
static struct ring_buffer_event *
rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer *buffer;
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_event *event;
int nr_loops = 0;
if (ring_buffer_iter_empty(iter))
return NULL;
cpu_buffer = iter->cpu_buffer;
buffer = cpu_buffer->buffer;
again:
/*
* We repeat when a timestamp is encountered. It is possible
* to get multiple timestamps from an interrupt entering just
* as one timestamp is about to be written. The max times
* that this can happen is the number of nested interrupts we
* can have. Nesting 10 deep of interrupts is clearly
* an anomaly.
*/
if (RB_WARN_ON(cpu_buffer, ++nr_loops > 10))
return NULL;
if (rb_per_cpu_empty(cpu_buffer))
return NULL;
event = rb_iter_head_event(iter);
switch (event->type) {
case RINGBUF_TYPE_PADDING:
rb_inc_iter(iter);
goto again;
case RINGBUF_TYPE_TIME_EXTEND:
/* Internal data, OK to advance */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_TIME_STAMP:
/* FIXME: not implemented */
rb_advance_iter(iter);
goto again;
case RINGBUF_TYPE_DATA:
if (ts) {
*ts = iter->read_stamp + event->time_delta;
ring_buffer_normalize_time_stamp(cpu_buffer->cpu, ts);
}
return event;
default:
BUG();
}
return NULL;
}
EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
/**
* ring_buffer_peek - peek at the next event to be read
* @buffer: The ring buffer to read
* @cpu: The cpu to peak at
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not consume the data.
*/
struct ring_buffer_event *
ring_buffer_peek(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
/**
* ring_buffer_iter_peek - peek at the next event to be read
* @iter: The ring buffer iterator
* @ts: The timestamp counter of this event.
*
* This will return the event that will be read next, but does
* not increment the iterator.
*/
struct ring_buffer_event *
ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
struct ring_buffer_event *event;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
/**
* ring_buffer_consume - return an event and consume it
* @buffer: The ring buffer to get the next event from
*
* Returns the next event in the ring buffer, and that event is consumed.
* Meaning, that sequential reads will keep returning a different event,
* and eventually empty the ring buffer if the producer is slower.
*/
struct ring_buffer_event *
ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_buffer_peek(buffer, cpu, ts);
if (!event)
goto out;
rb_advance_reader(cpu_buffer);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_consume);
/**
* ring_buffer_read_start - start a non consuming read of the buffer
* @buffer: The ring buffer to read from
* @cpu: The cpu buffer to iterate over
*
* This starts up an iteration through the buffer. It also disables
* the recording to the buffer until the reading is finished.
* This prevents the reading from being corrupted. This is not
* a consuming read, so a producer is not expected.
*
* Must be paired with ring_buffer_finish.
*/
struct ring_buffer_iter *
ring_buffer_read_start(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
struct ring_buffer_iter *iter;
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return NULL;
iter = kmalloc(sizeof(*iter), GFP_KERNEL);
if (!iter)
return NULL;
cpu_buffer = buffer->buffers[cpu];
iter->cpu_buffer = cpu_buffer;
atomic_inc(&cpu_buffer->record_disabled);
synchronize_sched();
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
__raw_spin_lock(&cpu_buffer->lock);
rb_iter_reset(iter);
__raw_spin_unlock(&cpu_buffer->lock);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return iter;
}
EXPORT_SYMBOL_GPL(ring_buffer_read_start);
/**
* ring_buffer_finish - finish reading the iterator of the buffer
* @iter: The iterator retrieved by ring_buffer_start
*
* This re-enables the recording to the buffer, and frees the
* iterator.
*/
void
ring_buffer_read_finish(struct ring_buffer_iter *iter)
{
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
atomic_dec(&cpu_buffer->record_disabled);
kfree(iter);
}
EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
/**
* ring_buffer_read - read the next item in the ring buffer by the iterator
* @iter: The ring buffer iterator
* @ts: The time stamp of the event read.
*
* This reads the next event in the ring buffer and increments the iterator.
*/
struct ring_buffer_event *
ring_buffer_read(struct ring_buffer_iter *iter, u64 *ts)
{
struct ring_buffer_event *event;
struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
unsigned long flags;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
event = rb_iter_peek(iter, ts);
if (!event)
goto out;
rb_advance_iter(iter);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return event;
}
EXPORT_SYMBOL_GPL(ring_buffer_read);
/**
* ring_buffer_size - return the size of the ring buffer (in bytes)
* @buffer: The ring buffer.
*/
unsigned long ring_buffer_size(struct ring_buffer *buffer)
{
return BUF_PAGE_SIZE * buffer->pages;
}
EXPORT_SYMBOL_GPL(ring_buffer_size);
static void
rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
{
cpu_buffer->head_page
= list_entry(cpu_buffer->pages.next, struct buffer_page, list);
local_set(&cpu_buffer->head_page->write, 0);
local_set(&cpu_buffer->head_page->page->commit, 0);
cpu_buffer->head_page->read = 0;
cpu_buffer->tail_page = cpu_buffer->head_page;
cpu_buffer->commit_page = cpu_buffer->head_page;
INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
local_set(&cpu_buffer->reader_page->write, 0);
local_set(&cpu_buffer->reader_page->page->commit, 0);
cpu_buffer->reader_page->read = 0;
cpu_buffer->overrun = 0;
cpu_buffer->entries = 0;
cpu_buffer->write_stamp = 0;
cpu_buffer->read_stamp = 0;
}
/**
* ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
* @buffer: The ring buffer to reset a per cpu buffer of
* @cpu: The CPU buffer to be reset
*/
void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
unsigned long flags;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
__raw_spin_lock(&cpu_buffer->lock);
rb_reset_cpu(cpu_buffer);
__raw_spin_unlock(&cpu_buffer->lock);
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
/**
* ring_buffer_reset - reset a ring buffer
* @buffer: The ring buffer to reset all cpu buffers
*/
void ring_buffer_reset(struct ring_buffer *buffer)
{
int cpu;
for_each_buffer_cpu(buffer, cpu)
ring_buffer_reset_cpu(buffer, cpu);
}
EXPORT_SYMBOL_GPL(ring_buffer_reset);
/**
* rind_buffer_empty - is the ring buffer empty?
* @buffer: The ring buffer to test
*/
int ring_buffer_empty(struct ring_buffer *buffer)
{
struct ring_buffer_per_cpu *cpu_buffer;
int cpu;
/* yes this is racy, but if you don't like the race, lock the buffer */
for_each_buffer_cpu(buffer, cpu) {
cpu_buffer = buffer->buffers[cpu];
if (!rb_per_cpu_empty(cpu_buffer))
return 0;
}
return 1;
}
EXPORT_SYMBOL_GPL(ring_buffer_empty);
/**
* ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
* @buffer: The ring buffer
* @cpu: The CPU buffer to test
*/
int ring_buffer_empty_cpu(struct ring_buffer *buffer, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer;
if (!cpumask_test_cpu(cpu, buffer->cpumask))
return 1;
cpu_buffer = buffer->buffers[cpu];
return rb_per_cpu_empty(cpu_buffer);
}
EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
/**
* ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
* @buffer_a: One buffer to swap with
* @buffer_b: The other buffer to swap with
*
* This function is useful for tracers that want to take a "snapshot"
* of a CPU buffer and has another back up buffer lying around.
* it is expected that the tracer handles the cpu buffer not being
* used at the moment.
*/
int ring_buffer_swap_cpu(struct ring_buffer *buffer_a,
struct ring_buffer *buffer_b, int cpu)
{
struct ring_buffer_per_cpu *cpu_buffer_a;
struct ring_buffer_per_cpu *cpu_buffer_b;
if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
!cpumask_test_cpu(cpu, buffer_b->cpumask))
return -EINVAL;
/* At least make sure the two buffers are somewhat the same */
if (buffer_a->pages != buffer_b->pages)
return -EINVAL;
if (ring_buffer_flags != RB_BUFFERS_ON)
return -EAGAIN;
if (atomic_read(&buffer_a->record_disabled))
return -EAGAIN;
if (atomic_read(&buffer_b->record_disabled))
return -EAGAIN;
cpu_buffer_a = buffer_a->buffers[cpu];
cpu_buffer_b = buffer_b->buffers[cpu];
if (atomic_read(&cpu_buffer_a->record_disabled))
return -EAGAIN;
if (atomic_read(&cpu_buffer_b->record_disabled))
return -EAGAIN;
/*
* We can't do a synchronize_sched here because this
* function can be called in atomic context.
* Normally this will be called from the same CPU as cpu.
* If not it's up to the caller to protect this.
*/
atomic_inc(&cpu_buffer_a->record_disabled);
atomic_inc(&cpu_buffer_b->record_disabled);
buffer_a->buffers[cpu] = cpu_buffer_b;
buffer_b->buffers[cpu] = cpu_buffer_a;
cpu_buffer_b->buffer = buffer_a;
cpu_buffer_a->buffer = buffer_b;
atomic_dec(&cpu_buffer_a->record_disabled);
atomic_dec(&cpu_buffer_b->record_disabled);
return 0;
}
EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
static void rb_remove_entries(struct ring_buffer_per_cpu *cpu_buffer,
struct buffer_data_page *bpage)
{
struct ring_buffer_event *event;
unsigned long head;
__raw_spin_lock(&cpu_buffer->lock);
for (head = 0; head < local_read(&bpage->commit);
head += rb_event_length(event)) {
event = __rb_data_page_index(bpage, head);
if (RB_WARN_ON(cpu_buffer, rb_null_event(event)))
return;
/* Only count data entries */
if (event->type != RINGBUF_TYPE_DATA)
continue;
cpu_buffer->entries--;
}
__raw_spin_unlock(&cpu_buffer->lock);
}
/**
* ring_buffer_alloc_read_page - allocate a page to read from buffer
* @buffer: the buffer to allocate for.
*
* This function is used in conjunction with ring_buffer_read_page.
* When reading a full page from the ring buffer, these functions
* can be used to speed up the process. The calling function should
* allocate a few pages first with this function. Then when it
* needs to get pages from the ring buffer, it passes the result
* of this function into ring_buffer_read_page, which will swap
* the page that was allocated, with the read page of the buffer.
*
* Returns:
* The page allocated, or NULL on error.
*/
void *ring_buffer_alloc_read_page(struct ring_buffer *buffer)
{
unsigned long addr;
struct buffer_data_page *bpage;
addr = __get_free_page(GFP_KERNEL);
if (!addr)
return NULL;
bpage = (void *)addr;
return bpage;
}
/**
* ring_buffer_free_read_page - free an allocated read page
* @buffer: the buffer the page was allocate for
* @data: the page to free
*
* Free a page allocated from ring_buffer_alloc_read_page.
*/
void ring_buffer_free_read_page(struct ring_buffer *buffer, void *data)
{
free_page((unsigned long)data);
}
/**
* ring_buffer_read_page - extract a page from the ring buffer
* @buffer: buffer to extract from
* @data_page: the page to use allocated from ring_buffer_alloc_read_page
* @cpu: the cpu of the buffer to extract
* @full: should the extraction only happen when the page is full.
*
* This function will pull out a page from the ring buffer and consume it.
* @data_page must be the address of the variable that was returned
* from ring_buffer_alloc_read_page. This is because the page might be used
* to swap with a page in the ring buffer.
*
* for example:
* rpage = ring_buffer_alloc_page(buffer);
* if (!rpage)
* return error;
* ret = ring_buffer_read_page(buffer, &rpage, cpu, 0);
* if (ret)
* process_page(rpage);
*
* When @full is set, the function will not return true unless
* the writer is off the reader page.
*
* Note: it is up to the calling functions to handle sleeps and wakeups.
* The ring buffer can be used anywhere in the kernel and can not
* blindly call wake_up. The layer that uses the ring buffer must be
* responsible for that.
*
* Returns:
* 1 if data has been transferred
* 0 if no data has been transferred.
*/
int ring_buffer_read_page(struct ring_buffer *buffer,
void **data_page, int cpu, int full)
{
struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
struct ring_buffer_event *event;
struct buffer_data_page *bpage;
unsigned long flags;
int ret = 0;
if (!data_page)
return 0;
bpage = *data_page;
if (!bpage)
return 0;
spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
/*
* rb_buffer_peek will get the next ring buffer if
* the current reader page is empty.
*/
event = rb_buffer_peek(buffer, cpu, NULL);
if (!event)
goto out;
/* check for data */
if (!local_read(&cpu_buffer->reader_page->page->commit))
goto out;
/*
* If the writer is already off of the read page, then simply
* switch the read page with the given page. Otherwise
* we need to copy the data from the reader to the writer.
*/
if (cpu_buffer->reader_page == cpu_buffer->commit_page) {
unsigned int read = cpu_buffer->reader_page->read;
if (full)
goto out;
/* The writer is still on the reader page, we must copy */
bpage = cpu_buffer->reader_page->page;
memcpy(bpage->data,
cpu_buffer->reader_page->page->data + read,
local_read(&bpage->commit) - read);
/* consume what was read */
cpu_buffer->reader_page += read;
} else {
/* swap the pages */
rb_init_page(bpage);
bpage = cpu_buffer->reader_page->page;
cpu_buffer->reader_page->page = *data_page;
cpu_buffer->reader_page->read = 0;
*data_page = bpage;
}
ret = 1;
/* update the entry counter */
rb_remove_entries(cpu_buffer, bpage);
out:
spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
return ret;
}
static ssize_t
rb_simple_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
{
long *p = filp->private_data;
char buf[64];
int r;
if (test_bit(RB_BUFFERS_DISABLED_BIT, p))
r = sprintf(buf, "permanently disabled\n");
else
r = sprintf(buf, "%d\n", test_bit(RB_BUFFERS_ON_BIT, p));
return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
}
static ssize_t
rb_simple_write(struct file *filp, const char __user *ubuf,
size_t cnt, loff_t *ppos)
{
long *p = filp->private_data;
char buf[64];
long val;
int ret;
if (cnt >= sizeof(buf))
return -EINVAL;
if (copy_from_user(&buf, ubuf, cnt))
return -EFAULT;
buf[cnt] = 0;
ret = strict_strtoul(buf, 10, &val);
if (ret < 0)
return ret;
if (val)
set_bit(RB_BUFFERS_ON_BIT, p);
else
clear_bit(RB_BUFFERS_ON_BIT, p);
(*ppos)++;
return cnt;
}
static struct file_operations rb_simple_fops = {
.open = tracing_open_generic,
.read = rb_simple_read,
.write = rb_simple_write,
};
static __init int rb_init_debugfs(void)
{
struct dentry *d_tracer;
struct dentry *entry;
d_tracer = tracing_init_dentry();
entry = debugfs_create_file("tracing_on", 0644, d_tracer,
&ring_buffer_flags, &rb_simple_fops);
if (!entry)
pr_warning("Could not create debugfs 'tracing_on' entry\n");
return 0;
}
fs_initcall(rb_init_debugfs);