Add ring buffer comment about shm

[lttng-ust.git] / libringbuffer / frontend.h

#ifndef _LINUX_RING_BUFFER_FRONTEND_H
#define _LINUX_RING_BUFFER_FRONTEND_H

/*
 * linux/ringbuffer/frontend.h
 *
 * (C) Copyright 2005-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Ring Buffer Library Synchronization Header (API).
 *
 * Author:
 *	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * See ring_buffer_frontend.c for more information on wait-free algorithms.
 *
 * Dual LGPL v2.1/GPL v2 license.
 */

#include <urcu/compiler.h>
#include <urcu/uatomic.h>

#include "smp.h"
/* Internal helpers */
#include "frontend_internal.h"

/* Buffer creation/removal and setup operations */

/*
 * switch_timer_interval is the time interval (in us) to fill sub-buffers with
 * padding to let readers get those sub-buffers.  Used for live streaming.
 *
 * read_timer_interval is the time interval (in us) to wake up pending readers.
 *
 * buf_addr is a pointer the the beginning of the preallocated buffer contiguous
 * address mapping. It is used only by RING_BUFFER_STATIC configuration. It can
 * be set to NULL for other backends.
 */

extern
struct shm_handle *channel_create(const struct lib_ring_buffer_config *config,
				const char *name, void *priv,
				void *buf_addr,
				size_t subbuf_size, size_t num_subbuf,
				unsigned int switch_timer_interval,
				unsigned int read_timer_interval);

/*
 * channel_destroy returns the private data pointer. It finalizes all channel's
 * buffers, waits for readers to release all references, and destroys the
 * channel.
 */
extern
void *channel_destroy(struct shm_handle *handle);


/* Buffer read operations */

/*
 * Iteration on channel cpumask needs to issue a read barrier to match the write
 * barrier in cpu hotplug. It orders the cpumask read before read of per-cpu
 * buffer data. The per-cpu buffer is never removed by cpu hotplug; teardown is
 * only performed at channel destruction.
 */
#define for_each_channel_cpu(cpu, chan)					\
	for_each_possible_cpu(cpu)

extern struct lib_ring_buffer *channel_get_ring_buffer(
				const struct lib_ring_buffer_config *config,
				struct channel *chan, int cpu);
extern int lib_ring_buffer_open_read(struct lib_ring_buffer *buf);
extern void lib_ring_buffer_release_read(struct lib_ring_buffer *buf);

/*
 * Read sequence: snapshot, many get_subbuf/put_subbuf, move_consumer.
 */
extern int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
				    unsigned long *consumed,
				    unsigned long *produced);
extern void lib_ring_buffer_move_consumer(struct lib_ring_buffer *buf,
					  unsigned long consumed_new);

extern int lib_ring_buffer_get_subbuf(struct lib_ring_buffer *buf,
				      unsigned long consumed);
extern void lib_ring_buffer_put_subbuf(struct lib_ring_buffer *buf);

/*
 * lib_ring_buffer_get_next_subbuf/lib_ring_buffer_put_next_subbuf are helpers
 * to read sub-buffers sequentially.
 */
static inline int lib_ring_buffer_get_next_subbuf(struct lib_ring_buffer *buf)
{
	int ret;

	ret = lib_ring_buffer_snapshot(buf, &buf->cons_snapshot,
				       &buf->prod_snapshot);
	if (ret)
		return ret;
	ret = lib_ring_buffer_get_subbuf(buf, buf->cons_snapshot);
	return ret;
}

static inline void lib_ring_buffer_put_next_subbuf(struct lib_ring_buffer *buf)
{
	lib_ring_buffer_put_subbuf(buf);
	lib_ring_buffer_move_consumer(buf, subbuf_align(buf->cons_snapshot,
						    shmp(buf->backend.chan)));
}

extern void channel_reset(struct channel *chan);
extern void lib_ring_buffer_reset(struct lib_ring_buffer *buf);

static inline
unsigned long lib_ring_buffer_get_offset(const struct lib_ring_buffer_config *config,
					 struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->offset);
}

static inline
unsigned long lib_ring_buffer_get_consumed(const struct lib_ring_buffer_config *config,
					   struct lib_ring_buffer *buf)
{
	return uatomic_read(&buf->consumed);
}

/*
 * Must call lib_ring_buffer_is_finalized before reading counters (memory
 * ordering enforced with respect to trace teardown).
 */
static inline
int lib_ring_buffer_is_finalized(const struct lib_ring_buffer_config *config,
				 struct lib_ring_buffer *buf)
{
	int finalized = CMM_ACCESS_ONCE(buf->finalized);
	/*
	 * Read finalized before counters.
	 */
	cmm_smp_rmb();
	return finalized;
}

static inline
int lib_ring_buffer_channel_is_finalized(const struct channel *chan)
{
	return chan->finalized;
}

static inline
int lib_ring_buffer_channel_is_disabled(const struct channel *chan)
{
	return uatomic_read(&chan->record_disabled);
}

static inline
unsigned long lib_ring_buffer_get_read_data_size(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return subbuffer_get_read_data_size(config, &buf->backend);
}

static inline
unsigned long lib_ring_buffer_get_records_count(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->records_count);
}

static inline
unsigned long lib_ring_buffer_get_records_overrun(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->records_overrun);
}

static inline
unsigned long lib_ring_buffer_get_records_lost_full(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->records_lost_full);
}

static inline
unsigned long lib_ring_buffer_get_records_lost_wrap(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->records_lost_wrap);
}

static inline
unsigned long lib_ring_buffer_get_records_lost_big(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->records_lost_big);
}

static inline
unsigned long lib_ring_buffer_get_records_read(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer *buf)
{
	return v_read(config, &buf->backend.records_read);
}

#endif /* _LINUX_RING_BUFFER_FRONTEND_H */