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

#ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H
#define _LTTNG_RING_BUFFER_FRONTEND_API_H

/*
 * libringbuffer/frontend_api.h
 *
 * Copyright (C) 2005-2012 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
 *
 * Ring Buffer Library Synchronization Header (buffer write API).
 *
 * Author:
 *      Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * See ring_buffer_frontend.c for more information on wait-free
 * algorithms.
 * See frontend.h for channel allocation and read-side API.
 */

#include "frontend.h"
#include <urcu-bp.h>
#include <urcu/compiler.h>

/**
 * lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
 *
 * Keeps a ring buffer nesting count as supplementary safety net to
 * ensure tracer client code will never trigger an endless recursion.
 * Returns the processor ID on success, -EPERM on failure (nesting count
 * too high).
 *
 * asm volatile and "memory" clobber prevent the compiler from moving
 * instructions out of the ring buffer nesting count. This is required to ensure
 * that probe side-effects which can cause recursion (e.g. unforeseen traps,
 * divisions by 0, ...) are triggered within the incremented nesting count
 * section.
 */
static inline
int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
{
	int cpu, nesting;

	cpu = lttng_ust_get_cpu();
	nesting = ++URCU_TLS(lib_ring_buffer_nesting);
	cmm_barrier();

	if (caa_unlikely(nesting > 4)) {
		WARN_ON_ONCE(1);
		URCU_TLS(lib_ring_buffer_nesting)--;
		rcu_read_unlock();
		return -EPERM;
	} else
		return cpu;
}

/**
 * lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
 */
static inline
void lib_ring_buffer_put_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
{
	cmm_barrier();
	URCU_TLS(lib_ring_buffer_nesting)--;		/* TLS */
}

/*
 * lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
 * part of the API per se.
 *
 * returns 0 if reserve ok, or 1 if the slow path must be taken.
 */
static inline
int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer_ctx *ctx,
				unsigned long *o_begin, unsigned long *o_end,
				unsigned long *o_old, size_t *before_hdr_pad)
{
	struct channel *chan = ctx->chan;
	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
	*o_begin = v_read(config, &buf->offset);
	*o_old = *o_begin;

	ctx->tsc = lib_ring_buffer_clock_read(chan);
	if ((int64_t) ctx->tsc == -EIO)
		return 1;

	/*
	 * Prefetch cacheline for read because we have to read the previous
	 * commit counter to increment it and commit seq value to compare it to
	 * the commit counter.
	 */
	//prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);

	if (last_tsc_overflow(config, buf, ctx->tsc))
		ctx->rflags |= RING_BUFFER_RFLAG_FULL_TSC;

	if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0))
		return 1;

	ctx->slot_size = record_header_size(config, chan, *o_begin,
					    before_hdr_pad, ctx);
	ctx->slot_size +=
		lib_ring_buffer_align(*o_begin + ctx->slot_size,
				      ctx->largest_align) + ctx->data_size;
	if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
		     > chan->backend.subbuf_size))
		return 1;

	/*
	 * Record fits in the current buffer and we are not on a switch
	 * boundary. It's safe to write.
	 */
	*o_end = *o_begin + ctx->slot_size;

	if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0))
		/*
		 * The offset_end will fall at the very beginning of the next
		 * subbuffer.
		 */
		return 1;

	return 0;
}

/**
 * lib_ring_buffer_reserve - Reserve space in a ring buffer.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input and output) Must be already initialized.
 *
 * Atomic wait-free slot reservation. The reserved space starts at the context
 * "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
 *
 * Return :
 *  0 on success.
 * -EAGAIN if channel is disabled.
 * -ENOSPC if event size is too large for packet.
 * -ENOBUFS if there is currently not enough space in buffer for the event.
 * -EIO if data cannot be written into the buffer for any other reason.
 */

static inline
int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
			    struct lttng_ust_lib_ring_buffer_ctx *ctx)
{
	struct channel *chan = ctx->chan;
	struct lttng_ust_shm_handle *handle = ctx->handle;
	struct lttng_ust_lib_ring_buffer *buf;
	unsigned long o_begin, o_end, o_old;
	size_t before_hdr_pad = 0;

	if (uatomic_read(&chan->record_disabled))
		return -EAGAIN;

	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
		buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
	else
		buf = shmp(handle, chan->backend.buf[0].shmp);
	if (uatomic_read(&buf->record_disabled))
		return -EAGAIN;
	ctx->buf = buf;

	/*
	 * Perform retryable operations.
	 */
	if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin,
						 &o_end, &o_old, &before_hdr_pad)))
		goto slow_path;

	if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
		     != o_old))
		goto slow_path;

	/*
	 * Atomically update last_tsc. This update races against concurrent
	 * atomic updates, but the race will always cause supplementary full TSC
	 * record headers, never the opposite (missing a full TSC record header
	 * when it would be needed).
	 */
	save_last_tsc(config, ctx->buf, ctx->tsc);

	/*
	 * Push the reader if necessary
	 */
	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);

	/*
	 * Clear noref flag for this subbuffer.
	 */
	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
				subbuf_index(o_end - 1, chan), handle);

	ctx->pre_offset = o_begin;
	ctx->buf_offset = o_begin + before_hdr_pad;
	return 0;
slow_path:
	return lib_ring_buffer_reserve_slow(ctx);
}

/**
 * lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
 * @config: ring buffer instance configuration.
 * @buf: buffer
 * @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
 *
 * This operation is completely reentrant : can be called while tracing is
 * active with absolutely no lock held.
 *
 * Note, however, that as a v_cmpxchg is used for some atomic operations and
 * requires to be executed locally for per-CPU buffers, this function must be
 * called from the CPU which owns the buffer for a ACTIVE flush, with preemption
 * disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
 */
static inline
void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config,
			    struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode,
			    struct lttng_ust_shm_handle *handle)
{
	lib_ring_buffer_switch_slow(buf, mode, handle);
}

/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */

/**
 * lib_ring_buffer_commit - Commit an record.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input arguments only)
 *
 * Atomic unordered slot commit. Increments the commit count in the
 * specified sub-buffer, and delivers it if necessary.
 */
static inline
void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config,
			    const struct lttng_ust_lib_ring_buffer_ctx *ctx)
{
	struct channel *chan = ctx->chan;
	struct lttng_ust_shm_handle *handle = ctx->handle;
	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
	unsigned long offset_end = ctx->buf_offset;
	unsigned long endidx = subbuf_index(offset_end - 1, chan);
	unsigned long commit_count;

	/*
	 * Must count record before incrementing the commit count.
	 */
	subbuffer_count_record(config, &buf->backend, endidx, handle);

	/*
	 * Order all writes to buffer before the commit count update that will
	 * determine that the subbuffer is full.
	 */
	cmm_smp_wmb();

	v_add(config, ctx->slot_size, &shmp_index(handle, buf->commit_hot, endidx)->cc);

	/*
	 * commit count read can race with concurrent OOO commit count updates.
	 * This is only needed for lib_ring_buffer_check_deliver (for
	 * non-polling delivery only) and for
	 * lib_ring_buffer_write_commit_counter.  The race can only cause the
	 * counter to be read with the same value more than once, which could
	 * cause :
	 * - Multiple delivery for the same sub-buffer (which is handled
	 *   gracefully by the reader code) if the value is for a full
	 *   sub-buffer. It's important that we can never miss a sub-buffer
	 *   delivery. Re-reading the value after the v_add ensures this.
	 * - Reading a commit_count with a higher value that what was actually
	 *   added to it for the lib_ring_buffer_write_commit_counter call
	 *   (again caused by a concurrent committer). It does not matter,
	 *   because this function is interested in the fact that the commit
	 *   count reaches back the reserve offset for a specific sub-buffer,
	 *   which is completely independent of the order.
	 */
	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc);

	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
				      commit_count, endidx, handle, ctx->tsc);
	/*
	 * Update used size at each commit. It's needed only for extracting
	 * ring_buffer buffers from vmcore, after crash.
	 */
	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
			offset_end, commit_count, handle);
}

/**
 * lib_ring_buffer_try_discard_reserve - Try discarding a record.
 * @config: ring buffer instance configuration.
 * @ctx: ring buffer context. (input arguments only)
 *
 * Only succeeds if no other record has been written after the record to
 * discard. If discard fails, the record must be committed to the buffer.
 *
 * Returns 0 upon success, -EPERM if the record cannot be discarded.
 */
static inline
int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
					const struct lttng_ust_lib_ring_buffer_ctx *ctx)
{
	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;

	/*
	 * We need to ensure that if the cmpxchg succeeds and discards the
	 * record, the next record will record a full TSC, because it cannot
	 * rely on the last_tsc associated with the discarded record to detect
	 * overflows. The only way to ensure this is to set the last_tsc to 0
	 * (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	 * timestamp in the next record.
	 *
	 * Note: if discard fails, we must leave the TSC in the record header.
	 * It is needed to keep track of TSC overflows for the following
	 * records.
	 */
	save_last_tsc(config, buf, 0ULL);

	if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
		   != end_offset))
		return -EPERM;
	else
		return 0;
}

static inline
void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
			    struct channel *chan)
{
	uatomic_inc(&chan->record_disabled);
}

static inline
void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
			   struct channel *chan)
{
	uatomic_dec(&chan->record_disabled);
}

static inline
void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
				    struct lttng_ust_lib_ring_buffer *buf)
{
	uatomic_inc(&buf->record_disabled);
}

static inline
void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
				   struct lttng_ust_lib_ring_buffer *buf)
{
	uatomic_dec(&buf->record_disabled);
}

#endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */
Commit	Line	Data
e92f3e28 MD	1	#ifndef _LTTNG_RING_BUFFER_FRONTEND_API_H
e92f3e28 MD	2	#define _LTTNG_RING_BUFFER_FRONTEND_API_H
852c2936 MD	3
852c2936 MD	4	/*
e92f3e28	5	* libringbuffer/frontend_api.h
852c2936	6	*
e92f3e28 MD	7	* Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	8	*
	9	* This library is free software; you can redistribute it and/or
	10	* modify it under the terms of the GNU Lesser General Public
	11	* License as published by the Free Software Foundation; only
	12	* version 2.1 of the License.
	13	*
	14	* This library is distributed in the hope that it will be useful,
	15	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	16	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	17	* Lesser General Public License for more details.
	18	*
	19	* You should have received a copy of the GNU Lesser General Public
	20	* License along with this library; if not, write to the Free Software
	21	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
852c2936 MD	22	*
	23	* Ring Buffer Library Synchronization Header (buffer write API).
	24	*
	25	* Author:
e92f3e28	26	* Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
852c2936	27	*
e92f3e28 MD	28	* See ring_buffer_frontend.c for more information on wait-free
	29	* algorithms.
	30	* See frontend.h for channel allocation and read-side API.
852c2936 MD	31	*/
852c2936 MD	32
4931a13e	33	#include "frontend.h"
9f3fdbc6 MD	34	#include <urcu-bp.h>
9f3fdbc6 MD	35	#include <urcu/compiler.h>
852c2936 MD	36
	37	/**
	38	* lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
	39	*
36cb884c MD	40	* Keeps a ring buffer nesting count as supplementary safety net to
	41	* ensure tracer client code will never trigger an endless recursion.
	42	* Returns the processor ID on success, -EPERM on failure (nesting count
	43	* too high).
852c2936 MD	44	*
	45	* asm volatile and "memory" clobber prevent the compiler from moving
	46	* instructions out of the ring buffer nesting count. This is required to ensure
	47	* that probe side-effects which can cause recursion (e.g. unforeseen traps,
	48	* divisions by 0, ...) are triggered within the incremented nesting count
	49	* section.
	50	*/
	51	static inline
4cfec15c	52	int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936 MD	53	{
	54	int cpu, nesting;
	55
2b2d6ff7	56	cpu = lttng_ust_get_cpu();
8c90a710	57	nesting = ++URCU_TLS(lib_ring_buffer_nesting);
9f3fdbc6	58	cmm_barrier();
852c2936	59
b5a3dfa5	60	if (caa_unlikely(nesting > 4)) {
852c2936	61	WARN_ON_ONCE(1);
8c90a710	62	URCU_TLS(lib_ring_buffer_nesting)--;
9f3fdbc6	63	rcu_read_unlock();
852c2936 MD	64	return -EPERM;
	65	} else
	66	return cpu;
	67	}
	68
	69	/**
	70	* lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
	71	*/
	72	static inline
4cfec15c	73	void lib_ring_buffer_put_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936	74	{
9f3fdbc6	75	cmm_barrier();
8c90a710	76	URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */
852c2936 MD	77	}
	78
	79	/*
	80	* lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
	81	* part of the API per se.
	82	*
	83	* returns 0 if reserve ok, or 1 if the slow path must be taken.
	84	*/
	85	static inline
4cfec15c MD	86	int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	87	struct lttng_ust_lib_ring_buffer_ctx *ctx,
852c2936 MD	88	unsigned long o_begin, unsigned long o_end,
	89	unsigned long o_old, size_t before_hdr_pad)
	90	{
	91	struct channel *chan = ctx->chan;
4cfec15c	92	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	93	*o_begin = v_read(config, &buf->offset);
	94	o_old = o_begin;
	95
	96	ctx->tsc = lib_ring_buffer_clock_read(chan);
	97	if ((int64_t) ctx->tsc == -EIO)
	98	return 1;
	99
	100	/*
	101	* Prefetch cacheline for read because we have to read the previous
	102	* commit counter to increment it and commit seq value to compare it to
	103	* the commit counter.
	104	*/
9f3fdbc6	105	//prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
852c2936 MD	106
	107	if (last_tsc_overflow(config, buf, ctx->tsc))
	108	ctx->rflags \|= RING_BUFFER_RFLAG_FULL_TSC;
	109
b5a3dfa5	110	if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0))
852c2936 MD	111	return 1;
	112
	113	ctx->slot_size = record_header_size(config, chan, *o_begin,
	114	before_hdr_pad, ctx);
	115	ctx->slot_size +=
	116	lib_ring_buffer_align(*o_begin + ctx->slot_size,
	117	ctx->largest_align) + ctx->data_size;
b5a3dfa5	118	if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
852c2936 MD	119	> chan->backend.subbuf_size))
	120	return 1;
	121
	122	/*
	123	* Record fits in the current buffer and we are not on a switch
	124	* boundary. It's safe to write.
	125	*/
	126	o_end = o_begin + ctx->slot_size;
1ad21f70 MD	127
	128	if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0))
	129	/*
	130	* The offset_end will fall at the very beginning of the next
	131	* subbuffer.
	132	*/
	133	return 1;
	134
852c2936 MD	135	return 0;
	136	}
	137
	138	/**
	139	* lib_ring_buffer_reserve - Reserve space in a ring buffer.
	140	* @config: ring buffer instance configuration.
	141	* @ctx: ring buffer context. (input and output) Must be already initialized.
	142	*
	143	* Atomic wait-free slot reservation. The reserved space starts at the context
	144	* "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
	145	*
	146	* Return :
	147	* 0 on success.
	148	* -EAGAIN if channel is disabled.
	149	* -ENOSPC if event size is too large for packet.
	150	* -ENOBUFS if there is currently not enough space in buffer for the event.
	151	* -EIO if data cannot be written into the buffer for any other reason.
	152	*/
	153
	154	static inline
4cfec15c MD	155	int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	156	struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936 MD	157	{
852c2936 MD	158	struct channel *chan = ctx->chan;
38fae1d3	159	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	160	struct lttng_ust_lib_ring_buffer *buf;
852c2936 MD	161	unsigned long o_begin, o_end, o_old;
	162	size_t before_hdr_pad = 0;
	163
9f3fdbc6	164	if (uatomic_read(&chan->record_disabled))
852c2936 MD	165	return -EAGAIN;
	166
	167	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
1d498196	168	buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
852c2936	169	else
1d498196	170	buf = shmp(handle, chan->backend.buf[0].shmp);
9f3fdbc6	171	if (uatomic_read(&buf->record_disabled))
852c2936 MD	172	return -EAGAIN;
	173	ctx->buf = buf;
	174
	175	/*
	176	* Perform retryable operations.
	177	*/
b5a3dfa5	178	if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin,
852c2936 MD	179	&o_end, &o_old, &before_hdr_pad)))
	180	goto slow_path;
	181
b5a3dfa5	182	if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
852c2936 MD	183	!= o_old))
	184	goto slow_path;
	185
	186	/*
	187	* Atomically update last_tsc. This update races against concurrent
	188	* atomic updates, but the race will always cause supplementary full TSC
	189	* record headers, never the opposite (missing a full TSC record header
	190	* when it would be needed).
	191	*/
	192	save_last_tsc(config, ctx->buf, ctx->tsc);
	193
	194	/*
	195	* Push the reader if necessary
	196	*/
	197	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
	198
	199	/*
	200	* Clear noref flag for this subbuffer.
	201	*/
	202	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
1d498196	203	subbuf_index(o_end - 1, chan), handle);
852c2936 MD	204
	205	ctx->pre_offset = o_begin;
	206	ctx->buf_offset = o_begin + before_hdr_pad;
	207	return 0;
	208	slow_path:
	209	return lib_ring_buffer_reserve_slow(ctx);
	210	}
	211
	212	/**
	213	* lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
	214	* @config: ring buffer instance configuration.
	215	* @buf: buffer
	216	* @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
	217	*
	218	* This operation is completely reentrant : can be called while tracing is
	219	* active with absolutely no lock held.
	220	*
	221	* Note, however, that as a v_cmpxchg is used for some atomic operations and
	222	* requires to be executed locally for per-CPU buffers, this function must be
	223	* called from the CPU which owns the buffer for a ACTIVE flush, with preemption
	224	* disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
	225	*/
	226	static inline
4cfec15c MD	227	void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	228	struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode,
38fae1d3	229	struct lttng_ust_shm_handle *handle)
852c2936	230	{
1d498196	231	lib_ring_buffer_switch_slow(buf, mode, handle);
852c2936 MD	232	}
	233
	234	/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */
	235
	236	/**
	237	* lib_ring_buffer_commit - Commit an record.
	238	* @config: ring buffer instance configuration.
	239	* @ctx: ring buffer context. (input arguments only)
	240	*
	241	* Atomic unordered slot commit. Increments the commit count in the
	242	* specified sub-buffer, and delivers it if necessary.
	243	*/
	244	static inline
4cfec15c MD	245	void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	246	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936 MD	247	{
852c2936 MD	248	struct channel *chan = ctx->chan;
38fae1d3	249	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	250	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	251	unsigned long offset_end = ctx->buf_offset;
	252	unsigned long endidx = subbuf_index(offset_end - 1, chan);
	253	unsigned long commit_count;
	254
	255	/*
	256	* Must count record before incrementing the commit count.
	257	*/
1d498196	258	subbuffer_count_record(config, &buf->backend, endidx, handle);
852c2936 MD	259
	260	/*
	261	* Order all writes to buffer before the commit count update that will
	262	* determine that the subbuffer is full.
	263	*/
9f3fdbc6	264	cmm_smp_wmb();
852c2936	265
4746ae29	266	v_add(config, ctx->slot_size, &shmp_index(handle, buf->commit_hot, endidx)->cc);
852c2936 MD	267
	268	/*
	269	* commit count read can race with concurrent OOO commit count updates.
	270	* This is only needed for lib_ring_buffer_check_deliver (for
	271	* non-polling delivery only) and for
	272	* lib_ring_buffer_write_commit_counter. The race can only cause the
	273	* counter to be read with the same value more than once, which could
	274	* cause :
	275	* - Multiple delivery for the same sub-buffer (which is handled
	276	* gracefully by the reader code) if the value is for a full
	277	* sub-buffer. It's important that we can never miss a sub-buffer
	278	* delivery. Re-reading the value after the v_add ensures this.
	279	* - Reading a commit_count with a higher value that what was actually
	280	* added to it for the lib_ring_buffer_write_commit_counter call
	281	* (again caused by a concurrent committer). It does not matter,
	282	* because this function is interested in the fact that the commit
	283	* count reaches back the reserve offset for a specific sub-buffer,
	284	* which is completely independent of the order.
	285	*/
4746ae29	286	commit_count = v_read(config, &shmp_index(handle, buf->commit_hot, endidx)->cc);
852c2936 MD	287
852c2936 MD	288	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
1b7b0501	289	commit_count, endidx, handle, ctx->tsc);
852c2936 MD	290	/*
	291	* Update used size at each commit. It's needed only for extracting
	292	* ring_buffer buffers from vmcore, after crash.
	293	*/
	294	lib_ring_buffer_write_commit_counter(config, buf, chan, endidx,
80249235	295	offset_end, commit_count, handle);
852c2936 MD	296	}
	297
	298	/**
	299	* lib_ring_buffer_try_discard_reserve - Try discarding a record.
	300	* @config: ring buffer instance configuration.
	301	* @ctx: ring buffer context. (input arguments only)
	302	*
	303	* Only succeeds if no other record has been written after the record to
	304	* discard. If discard fails, the record must be committed to the buffer.
	305	*
	306	* Returns 0 upon success, -EPERM if the record cannot be discarded.
	307	*/
	308	static inline
4cfec15c MD	309	int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	310	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936	311	{
4cfec15c	312	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	313	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;
	314
	315	/*
	316	* We need to ensure that if the cmpxchg succeeds and discards the
	317	* record, the next record will record a full TSC, because it cannot
	318	* rely on the last_tsc associated with the discarded record to detect
	319	* overflows. The only way to ensure this is to set the last_tsc to 0
	320	* (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	321	* timestamp in the next record.
	322	*
	323	* Note: if discard fails, we must leave the TSC in the record header.
	324	* It is needed to keep track of TSC overflows for the following
	325	* records.
	326	*/
	327	save_last_tsc(config, buf, 0ULL);
	328
b5a3dfa5	329	if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
852c2936 MD	330	!= end_offset))
	331	return -EPERM;
	332	else
	333	return 0;
	334	}
	335
	336	static inline
4cfec15c	337	void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	338	struct channel *chan)
852c2936 MD	339	{
9f3fdbc6	340	uatomic_inc(&chan->record_disabled);
852c2936 MD	341	}
	342
	343	static inline
4cfec15c	344	void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	345	struct channel *chan)
852c2936 MD	346	{
9f3fdbc6	347	uatomic_dec(&chan->record_disabled);
852c2936 MD	348	}
	349
	350	static inline
4cfec15c MD	351	void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	352	struct lttng_ust_lib_ring_buffer *buf)
852c2936	353	{
9f3fdbc6	354	uatomic_inc(&buf->record_disabled);
852c2936 MD	355	}
	356
	357	static inline
4cfec15c MD	358	void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	359	struct lttng_ust_lib_ring_buffer *buf)
852c2936	360	{
9f3fdbc6	361	uatomic_dec(&buf->record_disabled);
852c2936 MD	362	}
852c2936 MD	363
e92f3e28	364	#endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */