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    Subject[RFC PATCH 1/3] Unified trace buffer
    RFC RFC RFC RFC RFC!!!!

    Now did I get your attention that this is a request for comment patch.

    This is probably very buggy. I ran it as a back end for ftrace but only
    tested the irqsoff and ftrace tracers. The selftests are busted with it.

    But this is an attempt to get a unified buffering system that was
    talked about at the LPC meeting.

    I did not get a chance to implement all the event recording and printing
    in the debugfs/tracing/buffers directory. But I got enough to do
    some ftrace work with it.

    Now that it boots and runs (albeit, a bit buggy), I decided to post it.
    This is some idea that I had to handle this.

    I tried to make it as simple as possible. Basically we have:

    buffer = ring_buffer_alloc(size, flags, max_event_size, print_func, name);

    We can record either the fast way of reserving a part of the buffer:

    event = ring_buffer_lock_reserve(buffer, event_id, length, &flags);
    event->data = record_this_data;
    ring_buffer_unlock_commit(buffer, event, flags);

    Or if we already have the data together:

    ring_buffer_write(buffer, event_id, length, data);

    We can read by consuming or iterating:

    event = ring_buffer_consume(buffer);

    iter = ring_buffer_start(buffer, iter_flags);
    event = ring_buffer_read(iter, &next_cpu);
    ring_buffer_finish(iter);

    Note, the iteration part stops recording to the buffer. This is a feature.
    If you want producer/consumer, then you should be using the consumer.


    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    ---
    include/linux/ring_buffer.h | 138 +++
    kernel/trace/Kconfig | 4
    kernel/trace/Makefile | 1
    kernel/trace/ring_buffer.c | 1565 ++++++++++++++++++++++++++++++++++++++++++++
    4 files changed, 1708 insertions(+)

    Index: linux-compile.git/include/linux/ring_buffer.h
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-compile.git/include/linux/ring_buffer.h 2008-09-23 17:45:49.000000000 -0400
    @@ -0,0 +1,138 @@
    +#ifndef _LINUX_RING_BUFFER_H
    +#define _LINUX_RING_BUFFER_H
    +
    +#include <linux/mm.h>
    +#include <linux/seq_file.h>
    +
    +struct ring_buffer;
    +struct ring_buffer_iter;
    +
    +/*
    + * Don't reference this struct directly, use the inline items below.
    + */
    +struct ring_buffer_event {
    + unsigned long long counter;
    + short type;
    + short length;
    + char body[];
    +} __attribute__((__packed__));
    +
    +#define RB_EVNT_HDR_SIZE (sizeof(struct ring_buffer_event))
    +
    +static inline unsigned
    +ring_buffer_event_type(struct ring_buffer_event *event_handler)
    +{
    + return event_handler->type;
    +}
    +
    +static inline unsigned
    +ring_buffer_event_length(struct ring_buffer_event *event_handler)
    +{
    + return event_handler->length;
    +}
    +
    +static inline void *
    +ring_buffer_event_data(struct ring_buffer_event *event_handler)
    +{
    + return event_handler->body;
    +}
    +
    +static inline unsigned long long
    +ring_buffer_event_counter(struct ring_buffer_event *event_handler)
    +{
    + return event_handler->counter;
    +}
    +
    +struct ring_buffer_seq;
    +
    +unsigned long ring_buffer_max_event_size(struct ring_buffer *buffer);
    +
    +typedef void (*ring_buffer_print_func) (struct ring_buffer *buffer,
    + struct ring_buffer_seq *seq,
    + struct ring_buffer_event *event);
    +
    +struct ring_buffer_seq *ring_buffer_seq_alloc(gfp_t flags);
    +void ring_buffer_seq_free(struct ring_buffer_seq *seq);
    +unsigned ring_buffer_seq_length(struct ring_buffer_seq *seq);
    +void ring_buffer_seq_set_length(struct ring_buffer_seq *seq, unsigned len);
    +int ring_buffer_seq_printf(struct ring_buffer_seq *seq, const char *fmt, ...)
    + __attribute__ ((format (printf, 2, 3)));
    +int ring_buffer_seq_puts(struct ring_buffer_seq *seq, const char *str);
    +int ring_buffer_seq_putc(struct ring_buffer_seq *seq, unsigned char c);
    +int ring_buffer_seq_putmem(struct ring_buffer_seq *s, void *mem, size_t len);
    +int ring_buffer_seq_to_seqfile(struct seq_file *m, struct ring_buffer_seq *s);
    +int ring_buffer_seq_putmem_hex(struct ring_buffer_seq *s, void *mem, size_t len);
    +ssize_t ring_buffer_seq_copy_to_user(struct ring_buffer_seq *seq,
    + char __user *ubuf,
    + size_t cnt);
    +int ring_buffer_seq_to_mem(struct ring_buffer_seq *s, void *mem, size_t len);
    +void ring_buffer_seq_reset(struct ring_buffer_seq *s);
    +
    +void ring_buffer_lock(struct ring_buffer *buffer, unsigned long *flags);
    +void ring_buffer_unlock(struct ring_buffer *buffer, unsigned long flags);
    +
    +struct ring_buffer *
    +ring_buffer_alloc(unsigned long size, unsigned long flags,
    + unsigned long max_event_size,
    + ring_buffer_print_func print_func,
    + const char *name, ...);
    +void ring_buffer_free(struct ring_buffer *buffer);
    +
    +int
    +ring_buffer_register_event(struct ring_buffer *buffer, unsigned long length,
    + ring_buffer_print_func print_func,
    + int event_type,
    + const char *name, ...);
    +void *ring_buffer_lock_reserve(struct ring_buffer *buffer,
    + int event_type,
    + unsigned long length,
    + unsigned long *flags);
    +int ring_buffer_unlock_commit(struct ring_buffer *buffer,
    + void *data, unsigned long flags);
    +
    +int ring_buffer_rename(struct ring_buffer *buffer, char *new_name, ...);
    +
    +void *ring_buffer_write(struct ring_buffer *buffer,
    + int event_type,
    + unsigned long length,
    + void *event);
    +
    +enum ring_buffer_iter_flags {
    + RB_ITER_FL_SNAP = 1 << 0,
    +};
    +
    +struct ring_buffer_event *
    +ring_buffer_consume(struct ring_buffer *buffer);
    +
    +struct ring_buffer_iter *
    +ring_buffer_start(struct ring_buffer *buffer, unsigned flags);
    +void ring_buffer_finish(struct ring_buffer_iter *iter);
    +
    +struct ring_buffer_event *
    +ring_buffer_peek(struct ring_buffer_iter *iter, int *next_cpu);
    +
    +struct ring_buffer_event *
    +ring_buffer_read(struct ring_buffer_iter *iter, int *next_cpu);
    +
    +unsigned long ring_buffer_size(struct ring_buffer *buffer);
    +
    +void ring_buffer_reset_cpu(struct ring_buffer *buffer, int cpu);
    +
    +int ring_buffer_empty(struct ring_buffer *buffer);
    +
    +void ring_buffer_disable(struct ring_buffer *buffer);
    +void ring_buffer_enable(struct ring_buffer *buffer);
    +
    +void ring_buffer_snapshot(struct ring_buffer *buffer);
    +void ring_buffer_snapshot_cpu(struct ring_buffer *buffer, int cpu);
    +void ring_buffer_snapshot_one_cpu(struct ring_buffer *buffer, int cpu);
    +
    +unsigned long ring_buffer_entries(struct ring_buffer *buffer);
    +unsigned long ring_buffer_overruns(struct ring_buffer *buffer);
    +
    +enum ring_buffer_flags {
    + RB_FL_OVERWRITE = 1 << 0,
    + RB_FL_SNAPSHOT = 1 << 1,
    +};
    +
    +#endif /* _LINUX_RING_BUFFER_H */
    Index: linux-compile.git/kernel/trace/ring_buffer.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-compile.git/kernel/trace/ring_buffer.c 2008-09-24 00:46:40.000000000 -0400
    @@ -0,0 +1,1565 @@
    +/*
    + * Generic ring buffer
    + *
    + * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
    + */
    +#include <linux/ring_buffer.h>
    +#include <linux/spinlock.h>
    +#include <linux/debugfs.h>
    +#include <linux/uaccess.h>
    +#include <linux/module.h>
    +#include <linux/percpu.h>
    +#include <linux/init.h>
    +#include <linux/hash.h>
    +#include <linux/list.h>
    +#include <linux/fs.h>
    +
    +#include "trace.h"
    +
    +#define MAX_NAME_SIZE 256
    +#define RING_BUFFER_EVENT_DYN_START 1000
    +#define RB_EVENT_HASHBITS 10
    +#define RB_EVENT_HASHSIZE (1<<RB_EVENT_HASHBITS)
    +
    +/*
    + * head_page == tail_page && head == tail then buffer is empty.
    + */
    +struct ring_buffer_per_cpu {
    + int cpu;
    + struct ring_buffer *buffer;
    + raw_spinlock_t lock;
    + struct lock_class_key lock_key;
    + void **pages;
    + unsigned long head; /* read from head */
    + unsigned long tail; /* write to tail */
    + unsigned long head_page;
    + unsigned long tail_page;
    + unsigned long overrun;
    + unsigned long entries;
    +};
    +
    +struct ring_buffer {
    + char name[MAX_NAME_SIZE + 1];
    + ring_buffer_print_func default_func;
    + unsigned long size;
    + unsigned long next_event_type;
    + unsigned long max_event_size;
    + unsigned pages;
    + unsigned page_size;
    + unsigned flags;
    + int cpus;
    + atomic_t record_disabled;
    +
    + spinlock_t lock;
    + struct mutex mutex;
    +
    + struct ring_buffer_per_cpu *buffers[NR_CPUS];
    + struct list_head list;
    + struct list_head events;
    +
    + struct ring_buffer_per_cpu *snap_buffers[NR_CPUS];
    +
    + struct hlist_head event_hash[RB_EVENT_HASHSIZE];
    +
    + /* debugfs file entries */
    + struct dentry *dir_ent;
    + struct dentry *entry_dir;
    + struct dentry *text_ent;
    + struct dentry **binary_ents; /* per cpu */
    +};
    +
    +struct ring_buffer_event_holder {
    + struct ring_buffer *buffer;
    + struct list_head list;
    + struct hlist_node hash;
    + char *name;
    + unsigned event_type;
    + unsigned length;
    + ring_buffer_print_func print_func;
    +};
    +
    +struct ring_buffer_iter_per_cpu {
    + unsigned long head;
    + unsigned long head_page;
    +};
    +
    +struct ring_buffer_iter {
    + struct ring_buffer *buffer;
    + struct ring_buffer_iter_per_cpu buffers[NR_CPUS];
    + int next_cpu;
    + unsigned flags;
    +};
    +
    +struct ring_buffer_seq {
    + unsigned char buffer[PAGE_SIZE];
    + unsigned int len;
    + unsigned int readpos;
    +};
    +
    +static struct file_operations text_fops = {
    +#if 0
    + .open = text_open,
    + .read = seq_read,
    + .llseek = seq_lseek,
    + .release = text_release,
    +#endif
    +};
    +
    +static struct file_operations binary_fops = {
    +#if 0
    + .open = binary_open,
    + .read = seq_read,
    + .llseek = seq_lseek,
    + .release = binary_release,
    +#endif
    +};
    +
    +/* FIXME!!! */
    +unsigned long long
    +ring_buffer_next_counter(int cpu)
    +{
    + return sched_clock();
    +}
    +
    +DEFINE_MUTEX(buffer_mutex);
    +static LIST_HEAD(ring_buffer_list);
    +static struct dentry *buffer_dent;
    +#define TEMP_BUFFER_SIZE 1023
    +static char temp_buffer[TEMP_BUFFER_SIZE+1];
    +
    +static int ring_buffer_register_debugfs(struct ring_buffer *buffer)
    +{
    + struct dentry *tracing_dent;
    + struct dentry *dentry;
    + struct dentry *entry;
    + char name_buf[32];
    + int ret = -ENOMEM, i;
    +
    + if (!buffer_dent) {
    + tracing_dent = tracing_init_dentry();
    + buffer_dent = debugfs_create_dir("buffers", tracing_dent);
    + if (!buffer_dent) {
    + pr_warning("Could not create debugfs directory"
    + " 'tracing/buffers'\n");
    + return ret;
    + }
    + }
    +
    + buffer->binary_ents = kzalloc(sizeof(struct dentry *) * buffer->cpus,
    + GFP_KERNEL);
    + if (!buffer->binary_ents)
    + return ret;
    +
    + dentry = debugfs_create_dir(buffer->name, buffer_dent);
    + if (!dentry)
    + goto free_binary_ents;
    + buffer->dir_ent = dentry;
    +
    + entry = debugfs_create_file("text", 0444, dentry,
    + buffer, &text_fops);
    + if (!entry)
    + goto fail_free_dir;
    + buffer->text_ent = entry;
    +
    + for (i = 0; i < buffer->cpus; i++) {
    + snprintf(name_buf, 32, "binary%d", i);
    + entry = debugfs_create_file(name_buf, 0444, dentry,
    + buffer->buffers[i], &binary_fops);
    + if (!entry)
    + goto fail_free_ents;
    + buffer->binary_ents[i] = entry;
    + }
    +
    + return 0;
    +
    + fail_free_ents:
    + debugfs_remove(buffer->text_ent);
    + for (i = 0; i < buffer->cpus; i++) {
    + if (buffer->binary_ents[i])
    + debugfs_remove(buffer->binary_ents[i]);
    + }
    +
    + fail_free_dir:
    + kfree(buffer->binary_ents);
    + debugfs_remove(dentry);
    +
    + free_binary_ents:
    + kfree(buffer->binary_ents);
    + return -1;
    +}
    +
    +static void ring_buffer_unregister_debugfs(struct ring_buffer *buffer)
    +{
    + /* fast and simple for now */
    + debugfs_remove_recursive(buffer->dir_ent);
    +}
    +
    +static struct ring_buffer_per_cpu *
    +ring_buffer_allocate_cpu_buffer(struct ring_buffer *buffer, int cpu)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + int pages = buffer->pages;
    + int i;
    +
    + 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;
    + cpu_buffer->lock = (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED;
    +
    + cpu_buffer->pages = kzalloc_node(ALIGN(sizeof(void *) * pages,
    + cache_line_size()), GFP_KERNEL,
    + cpu_to_node(cpu));
    + if (!cpu_buffer->pages)
    + goto fail_free_buffer;
    +
    + for (i = 0; i < pages; i++) {
    + cpu_buffer->pages[i] = (void *)get_zeroed_page(GFP_KERNEL);
    + if (!cpu_buffer->pages[i])
    + goto fail_free_pages;
    + }
    +
    + return cpu_buffer;
    +
    + fail_free_pages:
    + for (i = 0; i < pages; i++) {
    + if (cpu_buffer->pages[i])
    + free_page((unsigned long)cpu_buffer->pages[i]);
    + }
    + kfree(cpu_buffer->pages);
    +
    + fail_free_buffer:
    + kfree(cpu_buffer);
    + return NULL;
    +}
    +
    +static void
    +ring_buffer_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
    +{
    + int i;
    +
    + for (i = 0; i < cpu_buffer->buffer->pages; i++) {
    + if (cpu_buffer->pages[i])
    + free_page((unsigned long)cpu_buffer->pages[i]);
    + }
    + kfree(cpu_buffer->pages);
    + kfree(cpu_buffer);
    +}
    +
    +struct ring_buffer *
    +ring_buffer_alloc(unsigned long size, unsigned long flags,
    + unsigned long max_event_size,
    + ring_buffer_print_func print_func,
    + const char *name, ...)
    +{
    + struct ring_buffer *buffer, *p;
    + va_list args;
    + int order = 0;
    + int ret = 0;
    + int cpu;
    +
    + /* For now, we only allow max of page size */
    + if (max_event_size > PAGE_SIZE) {
    + WARN_ON(1);
    + return NULL;
    + }
    + max_event_size = PAGE_SIZE;
    +
    + mutex_lock(&buffer_mutex);
    +
    + /* keep it in its own cache line */
    + buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
    + GFP_KERNEL);
    + if (!buffer)
    + goto fail_unlock;
    +
    + va_start(args, name);
    + vsnprintf(buffer->name, MAX_NAME_SIZE, name, args);
    + va_end(args);
    +
    + buffer->name[MAX_NAME_SIZE] = 0;
    + /* FIXME; this should be better than a linear search */
    + list_for_each_entry(p, &ring_buffer_list, list) {
    + if (strcmp(p->name, buffer->name) == 0) {
    + ret = -EBUSY;
    + break;
    + }
    + }
    + if (ret)
    + goto fail_free_buffer;
    +
    + buffer->page_size = 1 << order << PAGE_SHIFT;
    + buffer->next_event_type = RING_BUFFER_EVENT_DYN_START;
    + buffer->max_event_size = max_event_size;
    + INIT_LIST_HEAD(&buffer->events);
    +
    + buffer->default_func = print_func;
    + buffer->pages = (size + (buffer->page_size - 1)) / buffer->page_size;
    + buffer->flags = flags;
    +
    + /* need at least two pages */
    + if (buffer->pages == 1)
    + buffer->pages++;
    +
    + /* FIXME: do for only online CPUS */
    + buffer->cpus = num_possible_cpus();
    + for_each_possible_cpu(cpu) {
    + if (cpu >= buffer->cpus)
    + continue;
    + buffer->buffers[cpu] =
    + ring_buffer_allocate_cpu_buffer(buffer, cpu);
    + if (!buffer->buffers[cpu])
    + goto fail_free_buffers;
    + }
    +
    + if (flags & RB_FL_SNAPSHOT) {
    + for_each_possible_cpu(cpu) {
    + if (cpu >= buffer->cpus)
    + continue;
    + buffer->snap_buffers[cpu] =
    + ring_buffer_allocate_cpu_buffer(buffer, cpu);
    + if (!buffer->snap_buffers[cpu])
    + goto fail_free_snap_buffers;
    + }
    + }
    +
    + ret = ring_buffer_register_debugfs(buffer);
    + if (ret)
    + goto fail_free_snap_buffers;
    +
    + spin_lock_init(&buffer->lock);
    + mutex_init(&buffer->mutex);
    +
    + mutex_unlock(&buffer_mutex);
    +
    + return buffer;
    +
    + fail_free_snap_buffers:
    + if (!(flags & RB_FL_SNAPSHOT))
    + goto fail_free_buffers;
    +
    + for_each_possible_cpu(cpu) {
    + if (cpu >= buffer->cpus)
    + continue;
    + if (buffer->snap_buffers[cpu])
    + ring_buffer_free_cpu_buffer(buffer->snap_buffers[cpu]);
    + }
    +
    + fail_free_buffers:
    + for_each_possible_cpu(cpu) {
    + if (cpu >= buffer->cpus)
    + continue;
    + if (buffer->buffers[cpu])
    + ring_buffer_free_cpu_buffer(buffer->buffers[cpu]);
    + }
    +
    + fail_free_buffer:
    + kfree(buffer);
    +
    + fail_unlock:
    + mutex_unlock(&buffer_mutex);
    + return NULL;
    +}
    +
    +static struct ring_buffer_event_holder *
    +__ring_buffer_find_event(struct ring_buffer *buffer, int event_type)
    +{
    + struct ring_buffer_event_holder *p;
    + struct hlist_node *t;
    + unsigned long key;
    +
    + key = hash_long(event_type, RB_EVENT_HASHBITS);
    +
    + hlist_for_each_entry_rcu(p, t, &buffer->event_hash[key], hash) {
    + if (p->event_type == event_type)
    + return p;
    + }
    +
    + return NULL;
    +}
    +
    +/**
    + * ring_buffer_register_event - register an event to a ring buffer
    + * @buffer: the buffer to register the event to.
    + * @length: the length of the event
    + * @print_func: The pretty print output to handle this event.
    + * @event_type: Set the event type, or 0 to have one given
    + * @name: The name of this event, to show in the debugfs.
    + *
    + * This function allows events to be registered, as well as adding
    + * a function to handle how to show this event in text format.
    + * The event_type must be less than 1000, since that is where
    + * the dynamic event types start. Event types are unique to buffers.
    + */
    +int
    +ring_buffer_register_event(struct ring_buffer *buffer, unsigned long length,
    + ring_buffer_print_func print_func,
    + int event_type,
    + const char *name, ...)
    +{
    + struct ring_buffer_event_holder *ptr, *event;
    + struct list_head *p;
    + va_list args, args2;
    + unsigned long key;
    + int r;
    +
    + if (event_type >= RING_BUFFER_EVENT_DYN_START)
    + return -EINVAL;
    +
    + event = kzalloc(sizeof(*event), GFP_KERNEL);
    + if (!event)
    + return -ENOMEM;
    +
    + event->print_func = print_func;
    +
    + mutex_lock(&buffer->mutex);
    +
    + if (!event_type)
    + event_type = buffer->next_event_type++;
    +
    + ptr = __ring_buffer_find_event(buffer, event_type);
    + if (ptr) {
    + event_type = -EBUSY;
    + kfree(event);
    + goto out;
    + }
    +
    + va_start(args, name);
    + va_copy(args2, args);
    + r = vsnprintf(temp_buffer, TEMP_BUFFER_SIZE, name, args);
    +
    + event->name = kzalloc(r+1, GFP_KERNEL);
    + if (!event->name) {
    + va_end(args2);
    + va_end(args);
    + kfree(event);
    + return -ENOMEM;
    + }
    +
    + if (unlikely(r >= TEMP_BUFFER_SIZE))
    + vsnprintf(event->name, r+1, name, args2);
    + else
    + strcpy(event->name, temp_buffer);
    +
    + va_end(args2);
    + va_end(args);
    +
    + list_for_each(p, &buffer->events) {
    + ptr = list_entry(p, struct ring_buffer_event_holder, list);
    + r = strcmp(event->name, ptr->name);
    + if (!r) {
    + WARN_ON(1);
    + kfree(event->name);
    + kfree(event);
    + event = NULL;
    + goto out;
    + }
    + if (r < 0)
    + break;
    + }
    +
    + list_add_tail(&event->list, p);
    +
    + key = hash_long(event_type, RB_EVENT_HASHBITS);
    + hlist_add_head_rcu(&event->hash, &buffer->event_hash[key]);
    +
    + out:
    + mutex_unlock(&buffer->mutex);
    + return event_type;
    +}
    +
    +static void
    +ring_buffer_event_free(struct ring_buffer_event_holder *event)
    +{
    + kfree(event->name);
    + kfree(event);
    +}
    +
    +/**
    + * ring_buffer_free - free a ring buffer.
    + * @buffer: the buffer to free.
    + */
    +void
    +ring_buffer_free(struct ring_buffer *buffer)
    +{
    + struct ring_buffer_event_holder *event_holder, *n;
    + int cpu;
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++)
    + ring_buffer_free_cpu_buffer(buffer->buffers[cpu]);
    +
    + list_for_each_entry_safe(event_holder, n,
    + &buffer->events, list)
    + ring_buffer_event_free(event_holder);
    +
    + ring_buffer_unregister_debugfs(buffer);
    + kfree(buffer);
    +}
    +
    +/**
    + * ring_buffer_max_event_size - return max_event_size of the buffer
    + * @buffer: the buffer to get the max event size that is allowed.
    + *
    + * Returns the max event size allowed for the given buffer.
    + */
    +unsigned long
    +ring_buffer_max_event_size(struct ring_buffer *buffer)
    +{
    + return buffer->max_event_size;
    +}
    +
    +static inline int
    +ring_buffer_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
    +{
    + return cpu_buffer->head_page == cpu_buffer->tail_page &&
    + cpu_buffer->head == cpu_buffer->tail;
    +}
    +
    +static inline int
    +ring_buffer_null_event(struct ring_buffer_event *event)
    +{
    + return !event->type && !event->counter;
    +}
    +
    +static inline int
    +ring_buffer_short_event(struct ring_buffer *buffer, unsigned long ptr)
    +{
    + return ptr + RB_EVNT_HDR_SIZE > buffer->page_size;
    +}
    +
    +static void
    +ring_buffer_update_overflow(struct ring_buffer_per_cpu *cpu_buffer,
    + unsigned long head_page)
    +{
    + struct ring_buffer *buffer = cpu_buffer->buffer;
    + struct ring_buffer_event *event;
    + unsigned long head;
    +
    + for (head = 0; head < buffer->page_size; head += event->length) {
    + if (ring_buffer_short_event(buffer, head))
    + break;
    + event = cpu_buffer->pages[cpu_buffer->head_page] + head;
    + if (ring_buffer_null_event(event))
    + break;
    + cpu_buffer->overrun++;
    + cpu_buffer->entries--;
    + }
    +}
    +
    +static inline void
    +ring_buffer_inc_page(struct ring_buffer *buffer,
    + unsigned long *page)
    +{
    + (*page)++;
    + if (*page >= buffer->pages)
    + *page = 0;
    +}
    +
    +static struct ring_buffer_event *
    +ring_buffer_reserve_next_event(struct ring_buffer_per_cpu *cpu_buffer,
    + unsigned long length)
    +{
    + unsigned long head_page, tail_page, tail;
    + struct ring_buffer *buffer = cpu_buffer->buffer;
    + struct ring_buffer_event *event;
    +
    + if (length > buffer->page_size)
    + return NULL;
    +
    + tail_page = cpu_buffer->tail_page;
    + head_page = cpu_buffer->head_page;
    + tail = cpu_buffer->tail;
    +
    + BUG_ON(tail_page >= buffer->pages);
    + BUG_ON(head_page >= buffer->pages);
    +
    + if (tail + length > buffer->page_size) {
    + unsigned long next_page = tail_page;
    +
    + ring_buffer_inc_page(buffer, &next_page);
    +
    + if (next_page == head_page) {
    + if (!(buffer->flags & RB_FL_OVERWRITE))
    + return NULL;
    +
    + /* count overflows */
    + ring_buffer_update_overflow(cpu_buffer, head_page);
    +
    + ring_buffer_inc_page(buffer, &head_page);
    + cpu_buffer->head_page = head_page;
    + cpu_buffer->head = 0;
    + }
    +
    + if (!ring_buffer_short_event(buffer, tail)) {
    + event = cpu_buffer->pages[tail_page] + tail;
    + /* empty event */
    + event->counter = 0;
    + event->type = 0;
    + event->length = buffer->page_size - tail;
    + }
    +
    + tail = 0;
    + tail_page = next_page;
    + cpu_buffer->tail_page = tail_page;
    + cpu_buffer->tail = tail;
    + }
    +
    + BUG_ON(tail_page >= buffer->pages);
    + BUG_ON(ring_buffer_short_event(buffer, tail));
    +
    + event = cpu_buffer->pages[tail_page] + tail;
    + event->length = length;
    + cpu_buffer->entries++;
    +
    + return event;
    +}
    +
    +/**
    + * ring_buffer_lock_reserve - reserve a part of the buffer
    + * @buffer: the ring buffer to reserve from
    + * @event_type: the event type to reserve
    + * @length: the length of the data to reserve (excluding event header)
    + * @flags: a pointer to save the interrupt flags
    + *
    + * Returns a location on the ring buffer to copy directly to.
    + * 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.
    + */
    +void *ring_buffer_lock_reserve(struct ring_buffer *buffer,
    + int event_type,
    + unsigned long length,
    + unsigned long *flags)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_event *event;
    + int cpu;
    +
    + if (atomic_read(&buffer->record_disabled))
    + return NULL;
    +
    + raw_local_irq_save(*flags);
    + cpu = raw_smp_processor_id();
    + cpu_buffer = buffer->buffers[cpu];
    + __raw_spin_lock(&cpu_buffer->lock);
    +
    + if (atomic_read(&buffer->record_disabled))
    + goto no_record;
    +
    + length += RB_EVNT_HDR_SIZE;
    + length = ALIGN(length, 8);
    + WARN_ON(length > buffer->max_event_size);
    + event = ring_buffer_reserve_next_event(cpu_buffer, length);
    + if (!event)
    + goto no_record;
    +
    + event->counter = ring_buffer_next_counter(cpu_buffer->cpu);
    + event->type = event_type;
    +
    + return &event->body;
    +
    + no_record:
    + __raw_spin_unlock(&cpu_buffer->lock);
    + local_irq_restore(*flags);
    + return NULL;
    +}
    +
    +/**
    + * ring_buffer_unlock_commit - commit a reserved
    + * @buffer: The buffer to commit to
    + * @data: The data 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, void *data, unsigned long flags)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_event *event =
    + container_of(data, struct ring_buffer_event, body);
    +
    + int cpu = raw_smp_processor_id();
    +
    + cpu_buffer = buffer->buffers[cpu];
    +
    + cpu_buffer->tail += event->length;
    +
    + __raw_spin_unlock(&cpu_buffer->lock);
    + raw_local_irq_restore(flags);
    +
    + return 0;
    +}
    +
    +/**
    + * ring_buffer_write - write data to the buffer without reserving
    + * @buffer: The ring buffer to write to.
    + * @event_type: The event type 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.
    + */
    +void *ring_buffer_write(struct ring_buffer *buffer,
    + int event_type,
    + unsigned long length,
    + void *data)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_event *event;
    + unsigned long event_length, flags;
    + void *ret = NULL;
    + int cpu;
    +
    + if (atomic_read(&buffer->record_disabled))
    + return NULL;
    +
    + local_irq_save(flags);
    + cpu = raw_smp_processor_id();
    + cpu_buffer = buffer->buffers[cpu];
    + __raw_spin_lock(&cpu_buffer->lock);
    +
    + if (atomic_read(&buffer->record_disabled))
    + goto out;
    +
    + event_length = ALIGN(length + RB_EVNT_HDR_SIZE, 8);
    + event = ring_buffer_reserve_next_event(cpu_buffer, event_length);
    + if (!event)
    + goto out;
    +
    + event->counter = ring_buffer_next_counter(cpu_buffer->cpu);
    + event->type = event_type;
    + memcpy(&event->body, data, length);
    +
    + cpu_buffer->tail += event->length;
    +
    + ret = event->body;
    + out:
    + __raw_spin_unlock(&cpu_buffer->lock);
    + local_irq_restore(flags);
    +
    + return ret;
    +}
    +
    +/**
    + * ring_buffer_lock - lock the ring buffer
    + * @buffer: The ring buffer to lock
    + * @flags: The place to store the interrupt flags
    + *
    + * This locks all the per CPU buffers.
    + *
    + * Must be unlocked by ring_buffer_unlock.
    + */
    +void ring_buffer_lock(struct ring_buffer *buffer, unsigned long *flags)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + int cpu;
    +
    + local_irq_save(*flags);
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    +
    + cpu_buffer = buffer->buffers[cpu];
    + __raw_spin_lock(&cpu_buffer->lock);
    + }
    +}
    +
    +/**
    + * ring_buffer_unlock - unlock a locked buffer
    + * @buffer: The locked buffer to unlock
    + * @flags: The interrupt flags received by ring_buffer_lock
    + */
    +void ring_buffer_unlock(struct ring_buffer *buffer, unsigned long flags)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + int cpu;
    +
    + for (cpu = buffer->cpus - 1; cpu >= 0; cpu--) {
    +
    + cpu_buffer = buffer->buffers[cpu];
    + __raw_spin_unlock(&cpu_buffer->lock);
    + }
    +
    + local_irq_restore(flags);
    +}
    +
    +/**
    + * 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.
    + */
    +void ring_buffer_record_disable(struct ring_buffer *buffer)
    +{
    + atomic_inc(&buffer->record_disabled);
    +}
    +
    +/**
    + * 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);
    +}
    +
    +/**
    + * 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;
    +
    + cpu_buffer = buffer->buffers[cpu];
    + return cpu_buffer->entries;
    +}
    +
    +/**
    + * 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;
    +
    + cpu_buffer = buffer->buffers[cpu];
    + return cpu_buffer->overrun;
    +}
    +
    +/**
    + * 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 (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    + entries += cpu_buffer->entries;
    + }
    +
    + return 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 (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    + overruns += cpu_buffer->overrun;
    + }
    +
    + return overruns;
    +}
    +
    +static inline int
    +ring_buffer_iter_cpu_empty(struct ring_buffer_iter_per_cpu *cpu_iter,
    + struct ring_buffer_per_cpu *cpu_buffer)
    +{
    + return cpu_iter->head_page == cpu_buffer->tail_page &&
    + cpu_iter->head == cpu_buffer->tail;
    +}
    +
    +static inline struct ring_buffer_per_cpu *
    +iter_choose_buffer(struct ring_buffer_iter *iter, int cpu)
    +{
    + struct ring_buffer *buffer = iter->buffer;
    +
    + if (iter->flags & RB_ITER_FL_SNAP)
    + return buffer->snap_buffers[cpu];
    + else
    + return buffer->buffers[cpu];
    +}
    +
    +static void
    +ring_buffer_advance_head(struct ring_buffer_per_cpu *cpu_buffer)
    +{
    + struct ring_buffer *buffer = cpu_buffer->buffer;
    + struct ring_buffer_event *event;
    +
    + event = cpu_buffer->pages[cpu_buffer->head_page] + cpu_buffer->head;
    +
    + if (ring_buffer_short_event(buffer, cpu_buffer->head) ||
    + ring_buffer_null_event(event)) {
    + BUG_ON(cpu_buffer->head_page == cpu_buffer->tail_page);
    + ring_buffer_inc_page(buffer, &cpu_buffer->head_page);
    + cpu_buffer->head = 0;
    + return;
    + }
    +
    + BUG_ON((cpu_buffer->head_page == cpu_buffer->tail_page) &&
    + (cpu_buffer->head + event->length > cpu_buffer->tail));
    +
    + cpu_buffer->head += event->length;
    + if (ring_buffer_short_event(buffer, cpu_buffer->head)) {
    + ring_buffer_inc_page(buffer, &cpu_buffer->head_page);
    + cpu_buffer->head = 0;
    + return;
    + }
    +
    + /* check for end of page padding */
    + event = cpu_buffer->pages[cpu_buffer->head_page] + cpu_buffer->head;
    + if ((ring_buffer_short_event(buffer, cpu_buffer->head) ||
    + ring_buffer_null_event(event)) &&
    + (cpu_buffer->head_page != cpu_buffer->tail_page))
    + ring_buffer_advance_head(cpu_buffer);
    +}
    +
    +static void
    +ring_buffer_advance_iter(struct ring_buffer_iter *iter, int cpu)
    +{
    + struct ring_buffer *buffer = iter->buffer;
    + struct ring_buffer_iter_per_cpu *cpu_iter = &iter->buffers[cpu];
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_event *event;
    +
    + cpu_buffer = iter_choose_buffer(iter, cpu);
    + event = cpu_buffer->pages[cpu_iter->head_page] + cpu_iter->head;
    +
    + if (ring_buffer_short_event(buffer, cpu_iter->head) ||
    + ring_buffer_null_event(event)) {
    + BUG_ON(cpu_iter->head_page == cpu_buffer->tail_page);
    + ring_buffer_inc_page(buffer, &cpu_iter->head_page);
    + cpu_iter->head = 0;
    + return;
    + }
    +
    + BUG_ON((cpu_iter->head_page == cpu_buffer->tail_page) &&
    + (cpu_iter->head + event->length > cpu_buffer->tail));
    +
    + cpu_iter->head += event->length;
    + if (ring_buffer_short_event(buffer, cpu_iter->head)) {
    + ring_buffer_inc_page(buffer, &cpu_iter->head_page);
    + cpu_iter->head = 0;
    + return;
    + }
    +
    + /* check for end of page padding */
    + event = cpu_buffer->pages[cpu_iter->head_page] + cpu_iter->head;
    + if ((ring_buffer_short_event(buffer, cpu_iter->head) ||
    + ring_buffer_null_event(event)) &&
    + (cpu_iter->head_page != cpu_buffer->tail_page))
    + ring_buffer_advance_iter(iter, cpu);
    +}
    +
    +/**
    + * 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)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_event *event, *next_event = NULL;
    + int cpu, next_cpu = -1;
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    + if (ring_buffer_per_cpu_empty(cpu_buffer))
    + continue;
    +
    + event = cpu_buffer->pages[cpu_buffer->head_page] +
    + cpu_buffer->head;
    + if (unlikely(ring_buffer_short_event(buffer, cpu_buffer->head) ||
    + ring_buffer_null_event(event))) {
    + if (cpu_buffer->head_page == cpu_buffer->tail_page)
    + continue;
    + ring_buffer_inc_page(buffer, &cpu_buffer->head_page);
    + cpu_buffer->head = 0;
    +
    + if (ring_buffer_per_cpu_empty(cpu_buffer))
    + continue;
    + event = cpu_buffer->pages[cpu_buffer->head_page] +
    + cpu_buffer->head;
    + }
    +
    + if (!next_event || event->counter < next_event->counter) {
    + next_cpu = cpu;
    + next_event = event;
    + }
    + }
    +
    + if (!next_event)
    + return NULL;
    +
    + cpu_buffer = buffer->buffers[next_cpu];
    + ring_buffer_advance_head(cpu_buffer);
    + cpu_buffer->entries--;
    +
    + return next_event;
    +}
    +
    +/**
    + * ring_buffer_start - start a non consuming read of the buffer
    + * @buffer: The ring buffer to read from
    + * @iter_flags: control flags on how to read the buffer.
    + *
    + * 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.
    + *
    + * The iter_flags of RB_ITER_FL_SNAP will read the snapshot image
    + * and not the main buffer.
    + *
    + * Must be paired with ring_buffer_finish.
    + */
    +struct ring_buffer_iter *
    +ring_buffer_start(struct ring_buffer *buffer, unsigned iter_flags)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_iter *iter;
    + unsigned long flags;
    + int cpu;
    +
    + iter = kmalloc(sizeof(*iter), GFP_KERNEL);
    + if (!iter)
    + return NULL;
    +
    + iter->buffer = buffer;
    + iter->flags = iter_flags;
    +
    + WARN_ON((iter_flags & RB_ITER_FL_SNAP) &&
    + !(buffer->flags & RB_FL_SNAPSHOT));
    +
    + atomic_inc(&buffer->record_disabled);
    +
    + ring_buffer_lock(buffer, &flags);
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = iter_choose_buffer(iter, cpu);
    + iter->buffers[cpu].head = cpu_buffer->head;
    + iter->buffers[cpu].head_page = cpu_buffer->head_page;
    + }
    + ring_buffer_unlock(buffer, flags);
    +
    + iter->next_cpu = -1;
    +
    + return iter;
    +}
    +
    +/**
    + * 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_finish(struct ring_buffer_iter *iter)
    +{
    + struct ring_buffer *buffer = iter->buffer;
    +
    + atomic_dec(&buffer->record_disabled);
    + kfree(iter);
    +}
    +
    +/**
    + * ring_buffer_peek - peek at the next event to be read
    + * @iter: The ring buffer iterator
    + * @iter_next_cpu: The CPU that the next event belongs on
    + *
    + * This will return the event that will be read next, but does
    + * not increment the iterator.
    + */
    +struct ring_buffer_event *
    +ring_buffer_peek(struct ring_buffer_iter *iter, int *iter_next_cpu)
    +{
    + struct ring_buffer *buffer = iter->buffer;
    + struct ring_buffer_per_cpu *cpu_buffer;
    + struct ring_buffer_iter_per_cpu *cpu_iter;
    + struct ring_buffer_event *event, *next_event = NULL;
    + int cpu, next_cpu = -1;
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = iter_choose_buffer(iter, cpu);
    + cpu_iter = &iter->buffers[cpu];
    +
    + if (ring_buffer_iter_cpu_empty(cpu_iter, cpu_buffer))
    + continue;
    +
    + event = cpu_buffer->pages[cpu_iter->head_page] + cpu_iter->head;
    +
    + if (ring_buffer_short_event(buffer, cpu_iter->head) ||
    + ring_buffer_null_event(event)) {
    + if (cpu_iter->head_page == cpu_buffer->tail_page)
    + continue;
    + ring_buffer_inc_page(buffer, &cpu_iter->head_page);
    + cpu_iter->head = 0;
    +
    + if (ring_buffer_iter_cpu_empty(cpu_iter, cpu_buffer))
    + continue;
    +
    + event = cpu_buffer->pages[cpu_iter->head_page]
    + + cpu_iter->head;
    + }
    +
    + if (!next_event || event->counter < next_event->counter) {
    + next_cpu = cpu;
    + next_event = event;
    + }
    + }
    +
    + if (!next_event)
    + return NULL;
    +
    + if (iter_next_cpu)
    + *iter_next_cpu = next_cpu;
    +
    + return next_event;
    +}
    +
    +/**
    + * ring_buffer_read - read the next item in the ring buffer by the iterator
    + * @iter: The ring buffer iterator
    + * @iter_next_cpu: The CPU that the event was read from
    + *
    + * 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, int *iter_next_cpu)
    +{
    + struct ring_buffer_event *event;
    + int next_cpu;
    +
    + event = ring_buffer_peek(iter, &next_cpu);
    + if (!event)
    + return NULL;
    +
    + ring_buffer_advance_iter(iter, next_cpu);
    +
    + if (iter_next_cpu)
    + *iter_next_cpu = next_cpu;
    +
    + return event;
    +}
    +
    +/**
    + * 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 buffer->page_size * buffer->pages;
    +}
    +
    +/**
    + * ring_buffer_rename - rename the ring buffer
    + * @buffer: The ring buffer to rename
    + * @new_name: The new name to rename the ring buffer to
    + */
    +int ring_buffer_rename(struct ring_buffer *buffer, char *new_name, ...)
    +{
    + va_list args;
    + int ret;
    +
    + mutex_lock(&buffer_mutex);
    +
    + va_start(args, new_name);
    + vsnprintf(buffer->name, MAX_NAME_SIZE, new_name, args);
    + va_end(args);
    +
    + buffer->dir_ent = debugfs_rename(buffer_dent, buffer->dir_ent,
    + buffer_dent, buffer->name);
    + if (!buffer->dir_ent) {
    + WARN_ON(1);
    + ret = -EBUSY;
    + }
    +
    + mutex_unlock(&buffer_mutex);
    +
    + return ret;
    +}
    +
    +static void
    +__ring_buffer_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer, int cpu)
    +{
    + cpu_buffer->head_page = cpu_buffer->tail_page = 0;
    + cpu_buffer->head = cpu_buffer->tail = 0;
    + cpu_buffer->overrun = 0;
    + cpu_buffer->entries = 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;
    +
    + raw_local_irq_save(flags);
    + __raw_spin_lock(&cpu_buffer->lock);
    +
    + __ring_buffer_reset_cpu(cpu_buffer, cpu);
    +
    + __raw_spin_unlock(&cpu_buffer->lock);
    + raw_local_irq_restore(flags);
    +}
    +
    +/**
    + * 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 (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    + if (!ring_buffer_per_cpu_empty(cpu_buffer))
    + return 0;
    + }
    + return 1;
    +}
    +
    +/**
    + * 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;
    +
    + /* yes this is racy, but if you don't like the race, lock the buffer */
    + cpu_buffer = buffer->buffers[cpu];
    + return ring_buffer_per_cpu_empty(cpu_buffer);
    +}
    +
    +/**
    + * ring_buffer_snapshot_cpu - take a snapshot of a current ring buffer cpu buffer
    + * @buffer: The ring buffer
    + * @cpu: Take a snapshot of this CPU buffer
    + *
    + * A snapshot of the per CPU buffer is saved and the main buffer is
    + * replaced. This allows live traces to have a snap shot taken.
    + * This is very effective when needing to take maximums and still record
    + * new traces.
    + */
    +void ring_buffer_snapshot_cpu(struct ring_buffer *buffer, int cpu)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + unsigned long flags;
    +
    + raw_local_irq_save(flags);
    + cpu_buffer = buffer->buffers[cpu];
    +
    + __raw_spin_lock(&cpu_buffer->lock);
    + __ring_buffer_reset_cpu(buffer->snap_buffers[cpu], cpu);
    + buffer->buffers[cpu] = buffer->snap_buffers[cpu];
    + buffer->snap_buffers[cpu] = cpu_buffer;
    +
    + __raw_spin_unlock(&cpu_buffer->lock);
    + raw_local_irq_restore(flags);
    +}
    +
    +/**
    + * ring_buffer_snapshot_one_cpu - take a snapshot of cpu and zero the rest
    + * @buffer: The ring buffer
    + * @cpu: Take a snapshot of this CPU buffer
    + *
    + * A snapshot of the per CPU buffer is saved and the main buffer is
    + * replaced. This allows live traces to have a snap shot taken.
    + * This is very effective when needing to take maximums and still record
    + * new traces.
    + *
    + * This function will not only snapshot a particular CPU buffer, but it
    + * will also zero the others. This facilitates reading the snapshot buffer
    + * if only one buffer is of interest.
    + */
    +void ring_buffer_snapshot_one_cpu(struct ring_buffer *buffer, int snap_cpu)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + unsigned long flags;
    + int cpu;
    +
    + raw_local_irq_save(flags);
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    +
    + __raw_spin_lock(&cpu_buffer->lock);
    + __ring_buffer_reset_cpu(buffer->snap_buffers[cpu], cpu);
    + if (cpu == snap_cpu) {
    + buffer->buffers[cpu] = buffer->snap_buffers[cpu];
    + buffer->snap_buffers[cpu] = cpu_buffer;
    + }
    + __raw_spin_unlock(&cpu_buffer->lock);
    + }
    +
    + raw_local_irq_restore(flags);
    +}
    +
    +/**
    + * ring_buffer_snapshot - take a snapshot of the ring buffer
    + * @buffer: The ring buffer
    + *
    + * A snapshot of the entire ring buffer is saved, and can be
    + * retrieved later, even when we currently have a live trace
    + * recording.
    + */
    +void ring_buffer_snapshot(struct ring_buffer *buffer)
    +{
    + struct ring_buffer_per_cpu *cpu_buffer;
    + unsigned long flags;
    + int cpu;
    +
    + raw_local_irq_save(flags);
    +
    + for (cpu = 0; cpu < buffer->cpus; cpu++) {
    + cpu_buffer = buffer->buffers[cpu];
    +
    + __raw_spin_lock(&cpu_buffer->lock);
    + __ring_buffer_reset_cpu(buffer->snap_buffers[cpu], cpu);
    + buffer->buffers[cpu] = buffer->snap_buffers[cpu];
    + buffer->snap_buffers[cpu] = cpu_buffer;
    + __raw_spin_unlock(&cpu_buffer->lock);
    + }
    +
    + raw_local_irq_restore(flags);
    +}
    +
    +struct ring_buffer_seq *
    +ring_buffer_seq_alloc(gfp_t flags)
    +{
    + struct ring_buffer_seq *s;
    +
    + s = kzalloc(sizeof(*s), flags);
    + return s;
    +}
    +
    +void ring_buffer_seq_free(struct ring_buffer_seq *s)
    +{
    + kfree(s);
    +}
    +
    +unsigned ring_buffer_seq_length(struct ring_buffer_seq *seq)
    +{
    + return seq->len;
    +}
    +
    +void ring_buffer_seq_set_length(struct ring_buffer_seq *seq, unsigned len)
    +{
    + BUG_ON(len > PAGE_SIZE);
    + seq->len = len;
    +}
    +
    +/**
    + * ring_buffer_seq_printf - sequence printing of buffer information
    + * @s: buffer sequence descriptor
    + * @fmt: printf format string
    + *
    + * The tracer may use either sequence operations or its own
    + * copy to user routines. To simplify formating of a trace
    + * ring_buffer_seq_printf is used to store strings into a special
    + * buffer (@s). Then the output may be either used by
    + * the sequencer or pulled into another buffer.
    + */
    +int
    +ring_buffer_seq_printf(struct ring_buffer_seq *s, const char *fmt, ...)
    +{
    + int len = (PAGE_SIZE - 1) - s->len;
    + va_list ap;
    + int ret;
    +
    + if (!len)
    + return 0;
    +
    + va_start(ap, fmt);
    + ret = vsnprintf(s->buffer + s->len, len, fmt, ap);
    + va_end(ap);
    +
    + /* If we can't write it all, don't bother writing anything */
    + if (ret >= len)
    + return 0;
    +
    + s->len += ret;
    +
    + return len;
    +}
    +
    +/**
    + * ring_buffer_seq_puts - buffer sequence printing of simple string
    + * @s: buffer sequence descriptor
    + * @str: simple string to record
    + *
    + * The tracer may use either the sequence operations or its own
    + * copy to user routines. This function records a simple string
    + * into a special buffer (@s) for later retrieval by a sequencer
    + * or other mechanism.
    + */
    +int
    +ring_buffer_seq_puts(struct ring_buffer_seq *s, const char *str)
    +{
    + int len = strlen(str);
    +
    + if (len > ((PAGE_SIZE - 1) - s->len))
    + return 0;
    +
    + memcpy(s->buffer + s->len, str, len);
    + s->len += len;
    +
    + return len;
    +}
    +
    +int
    +ring_buffer_seq_putc(struct ring_buffer_seq *s, unsigned char c)
    +{
    + if (s->len >= (PAGE_SIZE - 1))
    + return 0;
    +
    + s->buffer[s->len++] = c;
    +
    + return 1;
    +}
    +
    +int
    +ring_buffer_seq_putmem(struct ring_buffer_seq *s, void *mem, size_t len)
    +{
    + if (len > ((PAGE_SIZE - 1) - s->len))
    + return 0;
    +
    + memcpy(s->buffer + s->len, mem, len);
    + s->len += len;
    +
    + return len;
    +}
    +
    +#define HEX_CHARS 17
    +static const char hex2asc[] = "0123456789abcdef";
    +
    +int
    +ring_buffer_seq_putmem_hex(struct ring_buffer_seq *s, void *mem, size_t len)
    +{
    + unsigned char hex[HEX_CHARS];
    + unsigned char *data = mem;
    + unsigned char byte;
    + int i, j;
    +
    + BUG_ON(len >= HEX_CHARS);
    +
    +#ifdef __BIG_ENDIAN
    + for (i = 0, j = 0; i < len; i++) {
    +#else
    + for (i = len-1, j = 0; i >= 0; i--) {
    +#endif
    + byte = data[i];
    +
    + hex[j++] = hex2asc[byte & 0x0f];
    + hex[j++] = hex2asc[byte >> 4];
    + }
    + hex[j++] = ' ';
    +
    + return ring_buffer_seq_putmem(s, hex, j);
    +}
    +
    +void
    +ring_buffer_seq_reset(struct ring_buffer_seq *s)
    +{
    + s->len = 0;
    + s->readpos = 0;
    +}
    +
    +ssize_t
    +ring_buffer_seq_copy_to_user(struct ring_buffer_seq *s,
    + char __user *ubuf, size_t cnt)
    +{
    + int len;
    + int ret;
    +
    + if (s->len <= s->readpos)
    + return -EBUSY;
    +
    + len = s->len - s->readpos;
    + if (cnt > len)
    + cnt = len;
    + ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
    + if (ret)
    + return -EFAULT;
    +
    + s->readpos += len;
    +
    + if (s->readpos >= s->len)
    + ring_buffer_seq_reset(s);
    +
    + return cnt;
    +}
    +
    +int
    +ring_buffer_seq_copy_to_mem(struct ring_buffer_seq *s,
    + void *mem, int cnt)
    +{
    + int len;
    +
    + if (s->len <= s->readpos)
    + return -EBUSY;
    +
    + len = s->len - s->readpos;
    + if (cnt > len)
    + cnt = len;
    + memcpy(mem, s->buffer + s->readpos, cnt);
    +
    + s->readpos += len;
    +
    + if (s->readpos >= s->len)
    + ring_buffer_seq_reset(s);
    +
    + return cnt;
    +}
    +
    +int
    +ring_buffer_seq_to_seqfile(struct seq_file *m, struct ring_buffer_seq *s)
    +{
    + int len = s->len >= PAGE_SIZE ? PAGE_SIZE - 1 : s->len;
    + int ret;
    +
    + s->buffer[len] = 0;
    + ret = seq_puts(m, s->buffer);
    + if (ret)
    + ring_buffer_seq_reset(s);
    + return ret;
    +}
    Index: linux-compile.git/kernel/trace/Kconfig
    ===================================================================
    --- linux-compile.git.orig/kernel/trace/Kconfig 2008-07-27 09:26:34.000000000 -0400
    +++ linux-compile.git/kernel/trace/Kconfig 2008-09-22 11:47:29.000000000 -0400
    @@ -15,6 +15,10 @@ config TRACING
    select DEBUG_FS
    select STACKTRACE

    +config RING_BUFFER
    + bool "ring buffer"
    + select DEBUG_FS
    +
    config FTRACE
    bool "Kernel Function Tracer"
    depends on HAVE_FTRACE
    Index: linux-compile.git/kernel/trace/Makefile
    ===================================================================
    --- linux-compile.git.orig/kernel/trace/Makefile 2008-07-27 09:26:34.000000000 -0400
    +++ linux-compile.git/kernel/trace/Makefile 2008-09-22 11:46:46.000000000 -0400
    @@ -11,6 +11,7 @@ obj-y += trace_selftest_dynamic.o
    endif

    obj-$(CONFIG_FTRACE) += libftrace.o
    +obj-$(CONFIG_RING_BUFFER) += ring_buffer.o

    obj-$(CONFIG_TRACING) += trace.o
    obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
    --


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