[lttng-ust.git] / liblttng-ust / lttng-ring-buffer-client.h

/*
 * lttng-ring-buffer-client.h
 *
 * LTTng lib ring buffer client template.
 *
 * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; only
 * version 2.1 of the License.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <stddef.h>
#include <stdint.h>
#include <lttng/ust-events.h>
#include "lttng/bitfield.h"
#include "clock.h"
#include "lttng-tracer.h"
#include "../libringbuffer/frontend_types.h"

#define LTTNG_COMPACT_EVENT_BITS       5
#define LTTNG_COMPACT_TSC_BITS         27

enum app_ctx_mode {
	APP_CTX_DISABLED,
	APP_CTX_ENABLED,
};

/*
 * Keep the natural field alignment for _each field_ within this structure if
 * you ever add/remove a field from this header. Packed attribute is not used
 * because gcc generates poor code on at least powerpc and mips. Don't ever
 * let gcc add padding between the structure elements.
 */

struct packet_header {
	/* Trace packet header */
	uint32_t magic;			/*
					 * Trace magic number.
					 * contains endianness information.
					 */
	uint8_t uuid[LTTNG_UST_UUID_LEN];
	uint32_t stream_id;
	uint64_t stream_instance_id;

	struct {
		/* Stream packet context */
		uint64_t timestamp_begin;	/* Cycle count at subbuffer start */
		uint64_t timestamp_end;		/* Cycle count at subbuffer end */
		uint64_t content_size;		/* Size of data in subbuffer */
		uint64_t packet_size;		/* Subbuffer size (include padding) */
		uint64_t packet_seq_num;	/* Packet sequence number */
		unsigned long events_discarded;	/*
						 * Events lost in this subbuffer since
						 * the beginning of the trace.
						 * (may overflow)
						 */
		uint32_t cpu_id;		/* CPU id associated with stream */
		uint8_t header_end;		/* End of header */
	} ctx;
};

struct lttng_client_ctx {
	size_t packet_context_len;
	size_t event_context_len;
};

static inline uint64_t lib_ring_buffer_clock_read(struct channel *chan)
{
	return trace_clock_read64();
}

static inline
size_t ctx_get_aligned_size(size_t offset, struct lttng_ctx *ctx,
		size_t ctx_len)
{
	size_t orig_offset = offset;

	if (caa_likely(!ctx))
		return 0;
	offset += lib_ring_buffer_align(offset, ctx->largest_align);
	offset += ctx_len;
	return offset - orig_offset;
}

static inline
void ctx_get_struct_size(struct lttng_ctx *ctx, size_t *ctx_len,
		enum app_ctx_mode mode)
{
	int i;
	size_t offset = 0;

	if (caa_likely(!ctx)) {
		*ctx_len = 0;
		return;
	}
	for (i = 0; i < ctx->nr_fields; i++) {
		if (mode == APP_CTX_ENABLED) {
			offset += ctx->fields[i].get_size(&ctx->fields[i], offset);
		} else {
			if (lttng_context_is_app(ctx->fields[i].event_field.name)) {
				/*
				 * Before UST 2.8, we cannot use the
				 * application context, because we
				 * cannot trust that the handler used
				 * for get_size is the same used for
				 * ctx_record, which would result in
				 * corrupted traces when tracing
				 * concurrently with application context
				 * register/unregister.
				 */
				offset += lttng_ust_dummy_get_size(&ctx->fields[i], offset);
			} else {
				offset += ctx->fields[i].get_size(&ctx->fields[i], offset);
			}
		}
	}
	*ctx_len = offset;
}

static inline
void ctx_record(struct lttng_ust_lib_ring_buffer_ctx *bufctx,
		struct lttng_channel *chan,
		struct lttng_ctx *ctx,
		enum app_ctx_mode mode)
{
	int i;

	if (caa_likely(!ctx))
		return;
	lib_ring_buffer_align_ctx(bufctx, ctx->largest_align);
	for (i = 0; i < ctx->nr_fields; i++) {
		if (mode == APP_CTX_ENABLED) {
			ctx->fields[i].record(&ctx->fields[i], bufctx, chan);
		} else {
			if (lttng_context_is_app(ctx->fields[i].event_field.name)) {
				/*
				 * Before UST 2.8, we cannot use the
				 * application context, because we
				 * cannot trust that the handler used
				 * for get_size is the same used for
				 * ctx_record, which would result in
				 * corrupted traces when tracing
				 * concurrently with application context
				 * register/unregister.
				 */
				lttng_ust_dummy_record(&ctx->fields[i], bufctx, chan);
			} else {
				ctx->fields[i].record(&ctx->fields[i], bufctx, chan);
			}
		}
	}
}

/*
 * record_header_size - Calculate the header size and padding necessary.
 * @config: ring buffer instance configuration
 * @chan: channel
 * @offset: offset in the write buffer
 * @pre_header_padding: padding to add before the header (output)
 * @ctx: reservation context
 *
 * Returns the event header size (including padding).
 *
 * The payload must itself determine its own alignment from the biggest type it
 * contains.
 */
static __inline__
size_t record_header_size(const struct lttng_ust_lib_ring_buffer_config *config,
				 struct channel *chan, size_t offset,
				 size_t *pre_header_padding,
				 struct lttng_ust_lib_ring_buffer_ctx *ctx,
				 struct lttng_client_ctx *client_ctx)
{
	struct lttng_channel *lttng_chan = channel_get_private(chan);
	struct lttng_event *event = ctx->priv;
	struct lttng_stack_ctx *lttng_ctx = ctx->priv2;
	size_t orig_offset = offset;
	size_t padding;

	switch (lttng_chan->header_type) {
	case 1:	/* compact */
		padding = lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
		offset += padding;
		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
			offset += sizeof(uint32_t);	/* id and timestamp */
		} else {
			/* Minimum space taken by LTTNG_COMPACT_EVENT_BITS id */
			offset += (LTTNG_COMPACT_EVENT_BITS + CHAR_BIT - 1) / CHAR_BIT;
			/* Align extended struct on largest member */
			offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
			offset += sizeof(uint32_t);	/* id */
			offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
			offset += sizeof(uint64_t);	/* timestamp */
		}
		break;
	case 2:	/* large */
		padding = lib_ring_buffer_align(offset, lttng_alignof(uint16_t));
		offset += padding;
		offset += sizeof(uint16_t);
		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
			offset += lib_ring_buffer_align(offset, lttng_alignof(uint32_t));
			offset += sizeof(uint32_t);	/* timestamp */
		} else {
			/* Align extended struct on largest member */
			offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
			offset += sizeof(uint32_t);	/* id */
			offset += lib_ring_buffer_align(offset, lttng_alignof(uint64_t));
			offset += sizeof(uint64_t);	/* timestamp */
		}
		break;
	default:
		padding = 0;
		WARN_ON_ONCE(1);
	}
	if (lttng_ctx) {
		/* 2.8+ probe ABI. */
		offset += ctx_get_aligned_size(offset, lttng_ctx->chan_ctx,
				client_ctx->packet_context_len);
		offset += ctx_get_aligned_size(offset, lttng_ctx->event_ctx,
				client_ctx->event_context_len);
	} else {
		/* Pre 2.8 probe ABI. */
		offset += ctx_get_aligned_size(offset, lttng_chan->ctx,
				client_ctx->packet_context_len);
		offset += ctx_get_aligned_size(offset, event->ctx,
				client_ctx->event_context_len);
	}
	*pre_header_padding = padding;
	return offset - orig_offset;
}

#include "../libringbuffer/api.h"
#include "lttng-rb-clients.h"

static
void lttng_write_event_header_slow(const struct lttng_ust_lib_ring_buffer_config *config,
				 struct lttng_ust_lib_ring_buffer_ctx *ctx,
				 uint32_t event_id);

/*
 * lttng_write_event_header
 *
 * Writes the event header to the offset (already aligned on 32-bits).
 *
 * @config: ring buffer instance configuration
 * @ctx: reservation context
 * @event_id: event ID
 */
static __inline__
void lttng_write_event_header(const struct lttng_ust_lib_ring_buffer_config *config,
			    struct lttng_ust_lib_ring_buffer_ctx *ctx,
			    uint32_t event_id)
{
	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
	struct lttng_event *event = ctx->priv;
	struct lttng_stack_ctx *lttng_ctx = ctx->priv2;

	if (caa_unlikely(ctx->rflags))
		goto slow_path;

	switch (lttng_chan->header_type) {
	case 1:	/* compact */
	{
		uint32_t id_time = 0;

		bt_bitfield_write(&id_time, uint32_t,
				0,
				LTTNG_COMPACT_EVENT_BITS,
				event_id);
		bt_bitfield_write(&id_time, uint32_t,
				LTTNG_COMPACT_EVENT_BITS,
				LTTNG_COMPACT_TSC_BITS,
				ctx->tsc);
		lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
		break;
	}
	case 2:	/* large */
	{
		uint32_t timestamp = (uint32_t) ctx->tsc;
		uint16_t id = event_id;

		lib_ring_buffer_write(config, ctx, &id, sizeof(id));
		lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint32_t));
		lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
		break;
	}
	default:
		WARN_ON_ONCE(1);
	}

	if (lttng_ctx) {
		/* 2.8+ probe ABI. */
		ctx_record(ctx, lttng_chan, lttng_ctx->chan_ctx, APP_CTX_ENABLED);
		ctx_record(ctx, lttng_chan, lttng_ctx->event_ctx, APP_CTX_ENABLED);
	} else {
		/* Pre 2.8 probe ABI. */
		ctx_record(ctx, lttng_chan, lttng_chan->ctx, APP_CTX_DISABLED);
		ctx_record(ctx, lttng_chan, event->ctx, APP_CTX_DISABLED);
	}
	lib_ring_buffer_align_ctx(ctx, ctx->largest_align);

	return;

slow_path:
	lttng_write_event_header_slow(config, ctx, event_id);
}

static
void lttng_write_event_header_slow(const struct lttng_ust_lib_ring_buffer_config *config,
				 struct lttng_ust_lib_ring_buffer_ctx *ctx,
				 uint32_t event_id)
{
	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
	struct lttng_event *event = ctx->priv;
	struct lttng_stack_ctx *lttng_ctx = ctx->priv2;

	switch (lttng_chan->header_type) {
	case 1:	/* compact */
		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
			uint32_t id_time = 0;

			bt_bitfield_write(&id_time, uint32_t,
					0,
					LTTNG_COMPACT_EVENT_BITS,
					event_id);
			bt_bitfield_write(&id_time, uint32_t,
					LTTNG_COMPACT_EVENT_BITS,
					LTTNG_COMPACT_TSC_BITS,
					ctx->tsc);
			lib_ring_buffer_write(config, ctx, &id_time, sizeof(id_time));
		} else {
			uint8_t id = 0;
			uint64_t timestamp = ctx->tsc;

			bt_bitfield_write(&id, uint8_t,
					0,
					LTTNG_COMPACT_EVENT_BITS,
					31);
			lib_ring_buffer_write(config, ctx, &id, sizeof(id));
			/* Align extended struct on largest member */
			lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
			lib_ring_buffer_write(config, ctx, &event_id, sizeof(event_id));
			lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
			lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
		}
		break;
	case 2:	/* large */
	{
		if (!(ctx->rflags & (RING_BUFFER_RFLAG_FULL_TSC | LTTNG_RFLAG_EXTENDED))) {
			uint32_t timestamp = (uint32_t) ctx->tsc;
			uint16_t id = event_id;

			lib_ring_buffer_write(config, ctx, &id, sizeof(id));
			lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint32_t));
			lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
		} else {
			uint16_t id = 65535;
			uint64_t timestamp = ctx->tsc;

			lib_ring_buffer_write(config, ctx, &id, sizeof(id));
			/* Align extended struct on largest member */
			lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
			lib_ring_buffer_write(config, ctx, &event_id, sizeof(event_id));
			lib_ring_buffer_align_ctx(ctx, lttng_alignof(uint64_t));
			lib_ring_buffer_write(config, ctx, &timestamp, sizeof(timestamp));
		}
		break;
	}
	default:
		WARN_ON_ONCE(1);
	}
	if (lttng_ctx) {
		/* 2.8+ probe ABI. */
		ctx_record(ctx, lttng_chan, lttng_ctx->chan_ctx, APP_CTX_ENABLED);
		ctx_record(ctx, lttng_chan, lttng_ctx->event_ctx, APP_CTX_ENABLED);
	} else {
		/* Pre 2.8 probe ABI. */
		ctx_record(ctx, lttng_chan, lttng_chan->ctx, APP_CTX_DISABLED);
		ctx_record(ctx, lttng_chan, event->ctx, APP_CTX_DISABLED);
	}
	lib_ring_buffer_align_ctx(ctx, ctx->largest_align);
}

static const struct lttng_ust_lib_ring_buffer_config client_config;

static uint64_t client_ring_buffer_clock_read(struct channel *chan)
{
	return lib_ring_buffer_clock_read(chan);
}

static
size_t client_record_header_size(const struct lttng_ust_lib_ring_buffer_config *config,
				 struct channel *chan, size_t offset,
				 size_t *pre_header_padding,
				 struct lttng_ust_lib_ring_buffer_ctx *ctx,
				 void *client_ctx)
{
	return record_header_size(config, chan, offset,
				  pre_header_padding, ctx, client_ctx);
}

/**
 * client_packet_header_size - called on buffer-switch to a new sub-buffer
 *
 * Return header size without padding after the structure. Don't use packed
 * structure because gcc generates inefficient code on some architectures
 * (powerpc, mips..)
 */
static size_t client_packet_header_size(void)
{
	return offsetof(struct packet_header, ctx.header_end);
}

static void client_buffer_begin(struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc,
				unsigned int subbuf_idx,
				struct lttng_ust_shm_handle *handle)
{
	struct channel *chan = shmp(handle, buf->backend.chan);
	struct packet_header *header =
		(struct packet_header *)
			lib_ring_buffer_offset_address(&buf->backend,
				subbuf_idx * chan->backend.subbuf_size,
				handle);
	struct lttng_channel *lttng_chan = channel_get_private(chan);
	uint64_t cnt = shmp_index(handle, buf->backend.buf_cnt, subbuf_idx)->seq_cnt;

	assert(header);
	if (!header)
		return;
	header->magic = CTF_MAGIC_NUMBER;
	memcpy(header->uuid, lttng_chan->uuid, sizeof(lttng_chan->uuid));
	header->stream_id = lttng_chan->id;
	header->stream_instance_id = buf->backend.cpu;
	header->ctx.timestamp_begin = tsc;
	header->ctx.timestamp_end = 0;
	header->ctx.content_size = ~0ULL; /* for debugging */
	header->ctx.packet_size = ~0ULL;
	header->ctx.packet_seq_num = chan->backend.num_subbuf * cnt + subbuf_idx;
	header->ctx.events_discarded = 0;
	header->ctx.cpu_id = buf->backend.cpu;
}

/*
 * offset is assumed to never be 0 here : never deliver a completely empty
 * subbuffer. data_size is between 1 and subbuf_size.
 */
static void client_buffer_end(struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc,
			      unsigned int subbuf_idx, unsigned long data_size,
			      struct lttng_ust_shm_handle *handle)
{
	struct channel *chan = shmp(handle, buf->backend.chan);
	struct packet_header *header =
		(struct packet_header *)
			lib_ring_buffer_offset_address(&buf->backend,
				subbuf_idx * chan->backend.subbuf_size,
				handle);
	unsigned long records_lost = 0;

	assert(header);
	if (!header)
		return;
	header->ctx.timestamp_end = tsc;
	header->ctx.content_size =
		(uint64_t) data_size * CHAR_BIT;		/* in bits */
	header->ctx.packet_size =
		(uint64_t) PAGE_ALIGN(data_size) * CHAR_BIT;	/* in bits */

	records_lost += lib_ring_buffer_get_records_lost_full(&client_config, buf);
	records_lost += lib_ring_buffer_get_records_lost_wrap(&client_config, buf);
	records_lost += lib_ring_buffer_get_records_lost_big(&client_config, buf);
	header->ctx.events_discarded = records_lost;
}

static int client_buffer_create(struct lttng_ust_lib_ring_buffer *buf, void *priv,
				int cpu, const char *name, struct lttng_ust_shm_handle *handle)
{
	return 0;
}

static void client_buffer_finalize(struct lttng_ust_lib_ring_buffer *buf, void *priv, int cpu, struct lttng_ust_shm_handle *handle)
{
}

static void client_content_size_field(const struct lttng_ust_lib_ring_buffer_config *config,
				      size_t *offset, size_t *length)
{
	*offset = offsetof(struct packet_header, ctx.content_size);
	*length = sizeof(((struct packet_header *) NULL)->ctx.content_size);
}

static void client_packet_size_field(const struct lttng_ust_lib_ring_buffer_config *config,
				      size_t *offset, size_t *length)
{
	*offset = offsetof(struct packet_header, ctx.packet_size);
	*length = sizeof(((struct packet_header *) NULL)->ctx.packet_size);
}

static struct packet_header *client_packet_header(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle)
{
	return lib_ring_buffer_read_offset_address(&buf->backend, 0, handle);
}

static int client_timestamp_begin(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *timestamp_begin)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*timestamp_begin = header->ctx.timestamp_begin;
	return 0;
}

static int client_timestamp_end(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *timestamp_end)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*timestamp_end = header->ctx.timestamp_end;
	return 0;
}

static int client_events_discarded(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *events_discarded)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*events_discarded = header->ctx.events_discarded;
	return 0;
}

static int client_content_size(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *content_size)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*content_size = header->ctx.content_size;
	return 0;
}

static int client_packet_size(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *packet_size)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*packet_size = header->ctx.packet_size;
	return 0;
}

static int client_stream_id(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *stream_id)
{
	struct channel *chan = shmp(handle, buf->backend.chan);
	struct lttng_channel *lttng_chan = channel_get_private(chan);

	*stream_id = lttng_chan->id;

	return 0;
}

static int client_current_timestamp(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *ts)
{
	struct channel *chan;

	chan = shmp(handle, handle->chan);
	*ts = client_ring_buffer_clock_read(chan);

	return 0;
}

static int client_sequence_number(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *seq)
{
	struct packet_header *header;

	header = client_packet_header(buf, handle);
	if (!header)
		return -1;
	*seq = header->ctx.packet_seq_num;
	return 0;
}

static int client_instance_id(struct lttng_ust_lib_ring_buffer *buf,
		struct lttng_ust_shm_handle *handle,
		uint64_t *id)
{
	*id = buf->backend.cpu;

	return 0;
}

static const
struct lttng_ust_client_lib_ring_buffer_client_cb client_cb = {
	.parent = {
		.ring_buffer_clock_read = client_ring_buffer_clock_read,
		.record_header_size = client_record_header_size,
		.subbuffer_header_size = client_packet_header_size,
		.buffer_begin = client_buffer_begin,
		.buffer_end = client_buffer_end,
		.buffer_create = client_buffer_create,
		.buffer_finalize = client_buffer_finalize,
		.content_size_field = client_content_size_field,
		.packet_size_field = client_packet_size_field,
	},
	.timestamp_begin = client_timestamp_begin,
	.timestamp_end = client_timestamp_end,
	.events_discarded = client_events_discarded,
	.content_size = client_content_size,
	.packet_size = client_packet_size,
	.stream_id = client_stream_id,
	.current_timestamp = client_current_timestamp,
	.sequence_number = client_sequence_number,
	.instance_id = client_instance_id,
};

static const struct lttng_ust_lib_ring_buffer_config client_config = {
	.cb.ring_buffer_clock_read = client_ring_buffer_clock_read,
	.cb.record_header_size = client_record_header_size,
	.cb.subbuffer_header_size = client_packet_header_size,
	.cb.buffer_begin = client_buffer_begin,
	.cb.buffer_end = client_buffer_end,
	.cb.buffer_create = client_buffer_create,
	.cb.buffer_finalize = client_buffer_finalize,
	.cb.content_size_field = client_content_size_field,
	.cb.packet_size_field = client_packet_size_field,

	.tsc_bits = LTTNG_COMPACT_TSC_BITS,
	.alloc = RING_BUFFER_ALLOC_PER_CPU,
	.sync = RING_BUFFER_SYNC_GLOBAL,
	.mode = RING_BUFFER_MODE_TEMPLATE,
	.backend = RING_BUFFER_PAGE,
	.output = RING_BUFFER_MMAP,
	.oops = RING_BUFFER_OOPS_CONSISTENCY,
	.ipi = RING_BUFFER_NO_IPI_BARRIER,
	.wakeup = LTTNG_CLIENT_WAKEUP,
	.client_type = LTTNG_CLIENT_TYPE,

	.cb_ptr = &client_cb.parent,
};

const struct lttng_ust_client_lib_ring_buffer_client_cb *LTTNG_CLIENT_CALLBACKS = &client_cb;

static
struct lttng_channel *_channel_create(const char *name,
				void *buf_addr,
				size_t subbuf_size, size_t num_subbuf,
				unsigned int switch_timer_interval,
				unsigned int read_timer_interval,
				unsigned char *uuid,
				uint32_t chan_id,
				const int *stream_fds, int nr_stream_fds,
				int64_t blocking_timeout)
{
	struct lttng_channel chan_priv_init;
	struct lttng_ust_shm_handle *handle;
	struct lttng_channel *lttng_chan;
	void *priv;

	memset(&chan_priv_init, 0, sizeof(chan_priv_init));
	memcpy(chan_priv_init.uuid, uuid, LTTNG_UST_UUID_LEN);
	chan_priv_init.id = chan_id;
	handle = channel_create(&client_config, name,
			&priv, __alignof__(struct lttng_channel),
			sizeof(struct lttng_channel),
			&chan_priv_init,
			buf_addr, subbuf_size, num_subbuf,
			switch_timer_interval, read_timer_interval,
			stream_fds, nr_stream_fds, blocking_timeout);
	if (!handle)
		return NULL;
	lttng_chan = priv;
	lttng_chan->handle = handle;
	lttng_chan->chan = shmp(handle, handle->chan);
	return lttng_chan;
}

static
void lttng_channel_destroy(struct lttng_channel *chan)
{
	channel_destroy(chan->chan, chan->handle, 1);
}

static
int lttng_event_reserve(struct lttng_ust_lib_ring_buffer_ctx *ctx,
		      uint32_t event_id)
{
	struct lttng_channel *lttng_chan = channel_get_private(ctx->chan);
	struct lttng_event *event = ctx->priv;
	struct lttng_stack_ctx *lttng_ctx = ctx->priv2;
	struct lttng_client_ctx client_ctx;
	int ret, cpu;

	/* Compute internal size of context structures. */

	if (lttng_ctx) {
		/* 2.8+ probe ABI. */
		ctx_get_struct_size(lttng_ctx->chan_ctx, &client_ctx.packet_context_len,
				APP_CTX_ENABLED);
		ctx_get_struct_size(lttng_ctx->event_ctx, &client_ctx.event_context_len,
				APP_CTX_ENABLED);
	} else {
		/* Pre 2.8 probe ABI. */
		ctx_get_struct_size(lttng_chan->ctx, &client_ctx.packet_context_len,
				APP_CTX_DISABLED);
		ctx_get_struct_size(event->ctx, &client_ctx.event_context_len,
				APP_CTX_DISABLED);
	}

	cpu = lib_ring_buffer_get_cpu(&client_config);
	if (cpu < 0)
		return -EPERM;
	ctx->cpu = cpu;

	switch (lttng_chan->header_type) {
	case 1:	/* compact */
		if (event_id > 30)
			ctx->rflags |= LTTNG_RFLAG_EXTENDED;
		break;
	case 2:	/* large */
		if (event_id > 65534)
			ctx->rflags |= LTTNG_RFLAG_EXTENDED;
		break;
	default:
		WARN_ON_ONCE(1);
	}

	ret = lib_ring_buffer_reserve(&client_config, ctx, &client_ctx);
	if (caa_unlikely(ret))
		goto put;
	if (caa_likely(ctx->ctx_len
			>= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) {
		if (lib_ring_buffer_backend_get_pages(&client_config, ctx,
				&ctx->backend_pages)) {
			ret = -EPERM;
			goto put;
		}
	}
	lttng_write_event_header(&client_config, ctx, event_id);
	return 0;
put:
	lib_ring_buffer_put_cpu(&client_config);
	return ret;
}

static
void lttng_event_commit(struct lttng_ust_lib_ring_buffer_ctx *ctx)
{
	lib_ring_buffer_commit(&client_config, ctx);
	lib_ring_buffer_put_cpu(&client_config);
}

static
void lttng_event_write(struct lttng_ust_lib_ring_buffer_ctx *ctx, const void *src,
		     size_t len)
{
	lib_ring_buffer_write(&client_config, ctx, src, len);
}

static
void lttng_event_strcpy(struct lttng_ust_lib_ring_buffer_ctx *ctx, const char *src,
		     size_t len)
{
	lib_ring_buffer_strcpy(&client_config, ctx, src, len, '#');
}

#if 0
static
wait_queue_head_t *lttng_get_reader_wait_queue(struct channel *chan)
{
	return &chan->read_wait;
}

static
wait_queue_head_t *lttng_get_hp_wait_queue(struct channel *chan)
{
	return &chan->hp_wait;
}
#endif //0

static
int lttng_is_finalized(struct channel *chan)
{
	return lib_ring_buffer_channel_is_finalized(chan);
}

static
int lttng_is_disabled(struct channel *chan)
{
	return lib_ring_buffer_channel_is_disabled(chan);
}

static
int lttng_flush_buffer(struct channel *chan, struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer *buf;
	int cpu;

	for_each_channel_cpu(cpu, chan) {
		int shm_fd, wait_fd, wakeup_fd;
		uint64_t memory_map_size;

		buf = channel_get_ring_buffer(&client_config, chan,
				cpu, handle, &shm_fd, &wait_fd,
				&wakeup_fd, &memory_map_size);
		lib_ring_buffer_switch(&client_config, buf,
				SWITCH_ACTIVE, handle);
	}
	return 0;
}

static struct lttng_transport lttng_relay_transport = {
	.name = "relay-" RING_BUFFER_MODE_TEMPLATE_STRING "-mmap",
	.ops = {
		.channel_create = _channel_create,
		.channel_destroy = lttng_channel_destroy,
		.u.has_strcpy = 1,
		.event_reserve = lttng_event_reserve,
		.event_commit = lttng_event_commit,
		.event_write = lttng_event_write,
		.packet_avail_size = NULL,	/* Would be racy anyway */
		//.get_reader_wait_queue = lttng_get_reader_wait_queue,
		//.get_hp_wait_queue = lttng_get_hp_wait_queue,
		.is_finalized = lttng_is_finalized,
		.is_disabled = lttng_is_disabled,
		.flush_buffer = lttng_flush_buffer,
		.event_strcpy = lttng_event_strcpy,
	},
	.client_config = &client_config,
};

void RING_BUFFER_MODE_TEMPLATE_INIT(void)
{
	DBG("LTT : ltt ring buffer client \"%s\" init\n",
		"relay-" RING_BUFFER_MODE_TEMPLATE_STRING "-mmap");
	lttng_transport_register(&lttng_relay_transport);
}

void RING_BUFFER_MODE_TEMPLATE_EXIT(void)
{
	DBG("LTT : ltt ring buffer client \"%s\" exit\n",
		"relay-" RING_BUFFER_MODE_TEMPLATE_STRING "-mmap");
	lttng_transport_unregister(&lttng_relay_transport);
}