Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/torvalds/linux-2.6

Conflicts:

	drivers/pci/dmar.c

1 files changed, 2014 insertions, 0 deletions

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
new file mode 100644
index 00000000000..94af1fe56bb
--- /dev/null
+++ b/kernel/trace/ring_buffer.c
@@ -0,0 +1,2014 @@
+/*
+ * 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/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>
+
+/* Up this if you want to test the TIME_EXTENTS and normalization */
+#define DEBUG_SHIFT 0
+
+/* FIXME!!! */
+u64 ring_buffer_time_stamp(int cpu)
+{
+	/* shift to debug/test normalization and TIME_EXTENTS */
+	return sched_clock() << DEBUG_SHIFT;
+}
+
+void ring_buffer_normalize_time_stamp(int cpu, u64 *ts)
+{
+	/* Just stupid testing the normalize function and deltas */
+	*ts >>= DEBUG_SHIFT;
+}
+
+#define RB_EVNT_HDR_SIZE (sizeof(struct ring_buffer_event))
+#define RB_ALIGNMENT_SHIFT	2
+#define RB_ALIGNMENT		(1 << RB_ALIGNMENT_SHIFT)
+#define RB_MAX_SMALL_DATA	28
+
+enum {
+	RB_LEN_TIME_EXTEND = 8,
+	RB_LEN_TIME_STAMP = 16,
+};
+
+/* inline for ring buffer fast paths */
+static inline 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_SHIFT;
+		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)
+{
+	return rb_event_length(event);
+}
+
+/* inline for ring buffer fast paths */
+static inline 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);
+}
+
+#define for_each_buffer_cpu(buffer, cpu)		\
+	for_each_cpu_mask(cpu, buffer->cpumask)
+
+#define TS_SHIFT	27
+#define TS_MASK		((1ULL << TS_SHIFT) - 1)
+#define TS_DELTA_TEST	(~TS_MASK)
+
+/*
+ * This hack stolen from mm/slob.c.
+ * We can store per page timing information in the page frame of the page.
+ * Thanks to Peter Zijlstra for suggesting this idea.
+ */
+struct buffer_page {
+	u64		 time_stamp;	/* page time stamp */
+	local_t		 write;		/* index for next write */
+	local_t		 commit;	/* write commited index */
+	unsigned	 read;		/* index for next read */
+	struct list_head list;		/* list of free pages */
+	void *page;			/* Actual data page */
+};
+
+/*
+ * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
+ * this issue out.
+ */
+static inline void free_buffer_page(struct buffer_page *bpage)
+{
+	if (bpage->page)
+		__free_page(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
+
+/*
+ * head_page == tail_page && head == tail then buffer is empty.
+ */
+struct ring_buffer_per_cpu {
+	int				cpu;
+	struct ring_buffer		*buffer;
+	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 long			size;
+	unsigned			pages;
+	unsigned			flags;
+	int				cpus;
+	cpumask_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;
+};
+
+#define RB_WARN_ON(buffer, cond)				\
+	do {							\
+		if (unlikely(cond)) {				\
+			atomic_inc(&buffer->record_disabled);	\
+			WARN_ON(1);				\
+		}						\
+	} while (0)
+
+#define RB_WARN_ON_RET(buffer, cond)				\
+	do {							\
+		if (unlikely(cond)) {				\
+			atomic_inc(&buffer->record_disabled);	\
+			WARN_ON(1);				\
+			return -1;				\
+		}						\
+	} while (0)
+
+#define RB_WARN_ON_ONCE(buffer, cond)				\
+	do {							\
+		static int once;				\
+		if (unlikely(cond) && !once) {			\
+			once++;					\
+			atomic_inc(&buffer->record_disabled);	\
+			WARN_ON(1);				\
+		}						\
+	} while (0)
+
+/**
+ * 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 *page, *tmp;
+
+	RB_WARN_ON_RET(cpu_buffer, head->next->prev != head);
+	RB_WARN_ON_RET(cpu_buffer, head->prev->next != head);
+
+	list_for_each_entry_safe(page, tmp, head, list) {
+		RB_WARN_ON_RET(cpu_buffer,
+			       page->list.next->prev != &page->list);
+		RB_WARN_ON_RET(cpu_buffer,
+			       page->list.prev->next != &page->list);
+	}
+
+	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 *page, *tmp;
+	unsigned long addr;
+	LIST_HEAD(pages);
+	unsigned i;
+
+	for (i = 0; i < nr_pages; i++) {
+		page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
+				    GFP_KERNEL, cpu_to_node(cpu_buffer->cpu));
+		if (!page)
+			goto free_pages;
+		list_add(&page->list, &pages);
+
+		addr = __get_free_page(GFP_KERNEL);
+		if (!addr)
+			goto free_pages;
+		page->page = (void *)addr;
+	}
+
+	list_splice(&pages, head);
+
+	rb_check_pages(cpu_buffer);
+
+	return 0;
+
+ free_pages:
+	list_for_each_entry_safe(page, tmp, &pages, list) {
+		list_del_init(&page->list);
+		free_buffer_page(page);
+	}
+	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 *page;
+	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->lock);
+	INIT_LIST_HEAD(&cpu_buffer->pages);
+
+	page = kzalloc_node(ALIGN(sizeof(*page), cache_line_size()),
+			    GFP_KERNEL, cpu_to_node(cpu));
+	if (!page)
+		goto fail_free_buffer;
+
+	cpu_buffer->reader_page = page;
+	addr = __get_free_page(GFP_KERNEL);
+	if (!addr)
+		goto fail_free_reader;
+	page->page = (void *)addr;
+
+	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 *page, *tmp;
+
+	list_del_init(&cpu_buffer->reader_page->list);
+	free_buffer_page(cpu_buffer->reader_page);
+
+	list_for_each_entry_safe(page, tmp, head, list) {
+		list_del_init(&page->list);
+		free_buffer_page(page);
+	}
+	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 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;
+
+	buffer->pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
+	buffer->flags = flags;
+
+	/* need at least two pages */
+	if (buffer->pages == 1)
+		buffer->pages++;
+
+	buffer->cpumask = cpu_possible_map;
+	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_buffer;
+
+	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_buffer:
+	kfree(buffer);
+	return NULL;
+}
+
+/**
+ * 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]);
+
+	kfree(buffer);
+}
+
+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 *page;
+	struct list_head *p;
+	unsigned i;
+
+	atomic_inc(&cpu_buffer->record_disabled);
+	synchronize_sched();
+
+	for (i = 0; i < nr_pages; i++) {
+		BUG_ON(list_empty(&cpu_buffer->pages));
+		p = cpu_buffer->pages.next;
+		page = list_entry(p, struct buffer_page, list);
+		list_del_init(&page->list);
+		free_buffer_page(page);
+	}
+	BUG_ON(list_empty(&cpu_buffer->pages));
+
+	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 *page;
+	struct list_head *p;
+	unsigned i;
+
+	atomic_inc(&cpu_buffer->record_disabled);
+	synchronize_sched();
+
+	for (i = 0; i < nr_pages; i++) {
+		BUG_ON(list_empty(pages));
+		p = pages->next;
+		page = list_entry(p, struct buffer_page, list);
+		list_del_init(&page->list);
+		list_add_tail(&page->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 *page, *tmp;
+	unsigned long buffer_size;
+	unsigned long addr;
+	LIST_HEAD(pages);
+	int i, cpu;
+
+	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 */
+		BUG_ON(nr_pages >= buffer->pages);
+
+		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;
+	 */
+	BUG_ON(nr_pages <= buffer->pages);
+	new_pages = nr_pages - buffer->pages;
+
+	for_each_buffer_cpu(buffer, cpu) {
+		for (i = 0; i < new_pages; i++) {
+			page = kzalloc_node(ALIGN(sizeof(*page),
+						  cache_line_size()),
+					    GFP_KERNEL, cpu_to_node(cpu));
+			if (!page)
+				goto free_pages;
+			list_add(&page->list, &pages);
+			addr = __get_free_page(GFP_KERNEL);
+			if (!addr)
+				goto free_pages;
+			page->page = (void *)addr;
+		}
+	}
+
+	for_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+		rb_insert_pages(cpu_buffer, &pages, new_pages);
+	}
+
+	BUG_ON(!list_empty(&pages));
+
+ out:
+	buffer->pages = nr_pages;
+	mutex_unlock(&buffer->mutex);
+
+	return size;
+
+ free_pages:
+	list_for_each_entry_safe(page, tmp, &pages, list) {
+		list_del_init(&page->list);
+		free_buffer_page(page);
+	}
+	return -ENOMEM;
+}
+
+static inline int rb_null_event(struct ring_buffer_event *event)
+{
+	return event->type == RINGBUF_TYPE_PADDING;
+}
+
+static inline void *__rb_page_index(struct buffer_page *page, unsigned index)
+{
+	return page->page + 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->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);
+		BUG_ON(rb_null_event(event));
+		/* 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 **page)
+{
+	struct list_head *p = (*page)->list.next;
+
+	if (p == &cpu_buffer->pages)
+		p = p->next;
+
+	*page = 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 inline 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 inline 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) {
+		RB_WARN_ON(cpu_buffer,
+			   cpu_buffer->commit_page == cpu_buffer->tail_page);
+		cpu_buffer->commit_page->commit =
+			cpu_buffer->commit_page->write;
+		rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
+		cpu_buffer->write_stamp = cpu_buffer->commit_page->time_stamp;
+	}
+
+	/* Now set the commit to the event's index */
+	local_set(&cpu_buffer->commit_page->commit, index);
+}
+
+static inline 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.
+	 */
+	while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
+		cpu_buffer->commit_page->commit =
+			cpu_buffer->commit_page->write;
+		rb_inc_page(cpu_buffer, &cpu_buffer->commit_page);
+		cpu_buffer->write_stamp = cpu_buffer->commit_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->commit =
+			cpu_buffer->commit_page->write;
+		barrier();
+	}
+}
+
+static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
+{
+	cpu_buffer->read_stamp = cpu_buffer->reader_page->time_stamp;
+	cpu_buffer->reader_page->read = 0;
+}
+
+static inline 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->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 inline 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 =
+			(RB_LEN_TIME_EXTEND + (RB_ALIGNMENT-1))
+			>> RB_ALIGNMENT_SHIFT;
+		break;
+
+	case RINGBUF_TYPE_TIME_STAMP:
+		event->len =
+			(RB_LEN_TIME_STAMP + (RB_ALIGNMENT-1))
+			>> RB_ALIGNMENT_SHIFT;
+		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 =
+				(length + (RB_ALIGNMENT-1))
+				>> RB_ALIGNMENT_SHIFT;
+		break;
+	default:
+		BUG();
+	}
+}
+
+static inline 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;
+	unsigned long tail, write;
+	struct ring_buffer *buffer = cpu_buffer->buffer;
+	struct ring_buffer_event *event;
+	unsigned long flags;
+
+	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;
+
+		spin_lock_irqsave(&cpu_buffer->lock, flags);
+
+		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 */
+		RB_WARN_ON(cpu_buffer, next_page == reader_page);
+
+		/*
+		 * 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 == cpu_buffer->commit_page)) {
+			WARN_ON_ONCE(1);
+			goto out_unlock;
+		}
+
+		if (next_page == head_page) {
+			if (!(buffer->flags & RB_FL_OVERWRITE)) {
+				/* reset write */
+				if (tail <= BUF_PAGE_SIZE)
+					local_set(&tail_page->write, tail);
+				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->commit, 0);
+			cpu_buffer->tail_page = next_page;
+
+			/* reread the time stamp */
+			*ts = ring_buffer_time_stamp(cpu_buffer->cpu);
+			cpu_buffer->tail_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);
+		}
+
+		spin_unlock_irqrestore(&cpu_buffer->lock, flags);
+
+		/* fail and let the caller try again */
+		return ERR_PTR(-EAGAIN);
+	}
+
+	/* We reserved something on the buffer */
+
+	BUG_ON(write > BUF_PAGE_SIZE);
+
+	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->time_stamp = *ts;
+
+	return event;
+
+ out_unlock:
+	spin_unlock_irqrestore(&cpu_buffer->lock, 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",
+		       *delta, *ts, 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->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;
+
+ again:
+	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))
+			goto again;
+
+		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 (atomic_read(&buffer->record_disabled))
+		return NULL;
+
+	/* If we are tracing schedule, we don't want to recurse */
+	resched = need_resched();
+	preempt_disable_notrace();
+
+	cpu = raw_smp_processor_id();
+
+	if (!cpu_isset(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:
+	if (resched)
+		preempt_enable_notrace();
+	else
+		preempt_enable_notrace();
+	return NULL;
+}
+
+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) {
+		if (per_cpu(rb_need_resched, cpu))
+			preempt_enable_no_resched_notrace();
+		else
+			preempt_enable_notrace();
+	} else
+		preempt_enable_no_resched_notrace();
+
+	return 0;
+}
+
+/**
+ * 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 (atomic_read(&buffer->record_disabled))
+		return -EBUSY;
+
+	resched = need_resched();
+	preempt_disable_notrace();
+
+	cpu = raw_smp_processor_id();
+
+	if (!cpu_isset(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:
+	if (resched)
+		preempt_enable_no_resched_notrace();
+	else
+		preempt_enable_notrace();
+
+	return ret;
+}
+
+static inline 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);
+}
+
+/**
+ * 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_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 (!cpu_isset(cpu, buffer->cpumask))
+		return;
+
+	cpu_buffer = buffer->buffers[cpu];
+	atomic_inc(&cpu_buffer->record_disabled);
+}
+
+/**
+ * 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 (!cpu_isset(cpu, buffer->cpumask))
+		return;
+
+	cpu_buffer = buffer->buffers[cpu];
+	atomic_dec(&cpu_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;
+
+	if (!cpu_isset(cpu, buffer->cpumask))
+		return 0;
+
+	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;
+
+	if (!cpu_isset(cpu, buffer->cpumask))
+		return 0;
+
+	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_each_buffer_cpu(buffer, 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_each_buffer_cpu(buffer, cpu) {
+		cpu_buffer = buffer->buffers[cpu];
+		overruns += cpu_buffer->overrun;
+	}
+
+	return overruns;
+}
+
+/**
+ * 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;
+
+	/* 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->time_stamp;
+}
+
+/**
+ * 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);
+}
+
+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;
+
+	spin_lock_irqsave(&cpu_buffer->lock, flags);
+
+ again:
+	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 */
+	RB_WARN_ON(cpu_buffer,
+		   cpu_buffer->reader_page->read > rb_page_size(reader));
+
+	/* 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->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:
+	spin_unlock_irqrestore(&cpu_buffer->lock, 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 */
+	BUG_ON(!reader);
+
+	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)) {
+		BUG_ON(iter->head_page == cpu_buffer->commit_page);
+		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.
+	 */
+	BUG_ON((iter->head_page == cpu_buffer->commit_page) &&
+	       (iter->head + length > rb_commit_index(cpu_buffer)));
+
+	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);
+}
+
+/**
+ * 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;
+	struct ring_buffer_event *event;
+	struct buffer_page *reader;
+
+	if (!cpu_isset(cpu, buffer->cpumask))
+		return NULL;
+
+	cpu_buffer = buffer->buffers[cpu];
+
+ again:
+	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;
+}
+
+/**
+ * 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 *buffer;
+	struct ring_buffer_per_cpu *cpu_buffer;
+	struct ring_buffer_event *event;
+
+	if (ring_buffer_iter_empty(iter))
+		return NULL;
+
+	cpu_buffer = iter->cpu_buffer;
+	buffer = cpu_buffer->buffer;
+
+ again:
+	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;
+}
+
+/**
+ * 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;
+	struct ring_buffer_event *event;
+
+	if (!cpu_isset(cpu, buffer->cpumask))
+		return NULL;
+
+	event = ring_buffer_peek(buffer, cpu, ts);
+	if (!event)
+		return NULL;
+
+	cpu_buffer = buffer->buffers[cpu];
+	rb_advance_reader(cpu_buffer);
+
+	return event;
+}
+
+/**
+ * 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 (!cpu_isset(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->lock, flags);
+	ring_buffer_iter_reset(iter);
+	spin_unlock_irqrestore(&cpu_buffer->lock, flags);
+
+	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_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);
+}
+
+/**
+ * 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;
+
+	event = ring_buffer_iter_peek(iter, ts);
+	if (!event)
+		return NULL;
+
+	rb_advance_iter(iter);
+
+	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 BUF_PAGE_SIZE * buffer->pages;
+}
+
+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->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->commit, 0);
+	cpu_buffer->reader_page->read = 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;
+
+	if (!cpu_isset(cpu, buffer->cpumask))
+		return;
+
+	spin_lock_irqsave(&cpu_buffer->lock, flags);
+
+	rb_reset_cpu(cpu_buffer);
+
+	spin_unlock_irqrestore(&cpu_buffer->lock, flags);
+}
+
+/**
+ * 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);
+}
+
+/**
+ * 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;
+}
+
+/**
+ * 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 (!cpu_isset(cpu, buffer->cpumask))
+		return 1;
+
+	cpu_buffer = buffer->buffers[cpu];
+	return rb_per_cpu_empty(cpu_buffer);
+}
+
+/**
+ * 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 (!cpu_isset(cpu, buffer_a->cpumask) ||
+	    !cpu_isset(cpu, buffer_b->cpumask))
+		return -EINVAL;
+
+	/* At least make sure the two buffers are somewhat the same */
+	if (buffer_a->size != buffer_b->size ||
+	    buffer_a->pages != buffer_b->pages)
+		return -EINVAL;
+
+	cpu_buffer_a = buffer_a->buffers[cpu];
+	cpu_buffer_b = buffer_b->buffers[cpu];
+
+	/*
+	 * 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;
+}
+