[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 <stddef.h>

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

#include "frontend.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)--;
		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,
				void *client_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, client_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,
			    void *client_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 (caa_unlikely(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 (caa_unlikely(!buf))
		return -EIO;
	if (caa_unlikely(uatomic_read(&buf->record_disabled)))
		return -EAGAIN;
	ctx->buf = buf;

	/*
	 * Perform retryable operations.
	 */
	if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, client_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, client_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;
	struct commit_counters_hot *cc_hot = shmp_index(handle,
						buf->commit_hot, endidx);

	if (caa_unlikely(!cc_hot))
		return;

	/*
	 * Must count record before incrementing the commit count.
	 */
	subbuffer_count_record(config, ctx, &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, &cc_hot->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, &cc_hot->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,
			offset_end, commit_count, handle, cc_hot);
}

/**
 * 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
b4051ad8 FD	33	#include <stddef.h>
b4051ad8 FD	34
9f3fdbc6 MD	35	#include <urcu-bp.h>
9f3fdbc6 MD	36	#include <urcu/compiler.h>
852c2936	37
b4051ad8 FD	38	#include "frontend.h"
b4051ad8 FD	39
852c2936 MD	40	/**
	41	* lib_ring_buffer_get_cpu - Precedes ring buffer reserve/commit.
	42	*
36cb884c MD	43	* Keeps a ring buffer nesting count as supplementary safety net to
	44	* ensure tracer client code will never trigger an endless recursion.
	45	* Returns the processor ID on success, -EPERM on failure (nesting count
	46	* too high).
852c2936 MD	47	*
	48	* asm volatile and "memory" clobber prevent the compiler from moving
	49	* instructions out of the ring buffer nesting count. This is required to ensure
	50	* that probe side-effects which can cause recursion (e.g. unforeseen traps,
	51	* divisions by 0, ...) are triggered within the incremented nesting count
	52	* section.
	53	*/
	54	static inline
4cfec15c	55	int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936 MD	56	{
	57	int cpu, nesting;
	58
2b2d6ff7	59	cpu = lttng_ust_get_cpu();
8c90a710	60	nesting = ++URCU_TLS(lib_ring_buffer_nesting);
9f3fdbc6	61	cmm_barrier();
852c2936	62
b5a3dfa5	63	if (caa_unlikely(nesting > 4)) {
852c2936	64	WARN_ON_ONCE(1);
8c90a710	65	URCU_TLS(lib_ring_buffer_nesting)--;
852c2936 MD	66	return -EPERM;
	67	} else
	68	return cpu;
	69	}
	70
	71	/**
	72	* lib_ring_buffer_put_cpu - Follows ring buffer reserve/commit.
	73	*/
	74	static inline
4cfec15c	75	void lib_ring_buffer_put_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936	76	{
9f3fdbc6	77	cmm_barrier();
8c90a710	78	URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */
852c2936 MD	79	}
	80
	81	/*
	82	* lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
	83	* part of the API per se.
	84	*
	85	* returns 0 if reserve ok, or 1 if the slow path must be taken.
	86	*/
	87	static inline
4cfec15c MD	88	int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	89	struct lttng_ust_lib_ring_buffer_ctx *ctx,
e56bb47c	90	void *client_ctx,
852c2936 MD	91	unsigned long o_begin, unsigned long o_end,
	92	unsigned long o_old, size_t before_hdr_pad)
	93	{
	94	struct channel *chan = ctx->chan;
4cfec15c	95	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	96	*o_begin = v_read(config, &buf->offset);
	97	o_old = o_begin;
	98
	99	ctx->tsc = lib_ring_buffer_clock_read(chan);
	100	if ((int64_t) ctx->tsc == -EIO)
	101	return 1;
	102
	103	/*
	104	* Prefetch cacheline for read because we have to read the previous
	105	* commit counter to increment it and commit seq value to compare it to
	106	* the commit counter.
	107	*/
9f3fdbc6	108	//prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
852c2936 MD	109
	110	if (last_tsc_overflow(config, buf, ctx->tsc))
	111	ctx->rflags \|= RING_BUFFER_RFLAG_FULL_TSC;
	112
b5a3dfa5	113	if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0))
852c2936 MD	114	return 1;
	115
	116	ctx->slot_size = record_header_size(config, chan, *o_begin,
e56bb47c	117	before_hdr_pad, ctx, client_ctx);
852c2936 MD	118	ctx->slot_size +=
	119	lib_ring_buffer_align(*o_begin + ctx->slot_size,
	120	ctx->largest_align) + ctx->data_size;
b5a3dfa5	121	if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
852c2936 MD	122	> chan->backend.subbuf_size))
	123	return 1;
	124
	125	/*
	126	* Record fits in the current buffer and we are not on a switch
	127	* boundary. It's safe to write.
	128	*/
	129	o_end = o_begin + ctx->slot_size;
1ad21f70 MD	130
	131	if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0))
	132	/*
	133	* The offset_end will fall at the very beginning of the next
	134	* subbuffer.
	135	*/
	136	return 1;
	137
852c2936 MD	138	return 0;
	139	}
	140
	141	/**
	142	* lib_ring_buffer_reserve - Reserve space in a ring buffer.
	143	* @config: ring buffer instance configuration.
	144	* @ctx: ring buffer context. (input and output) Must be already initialized.
	145	*
	146	* Atomic wait-free slot reservation. The reserved space starts at the context
	147	* "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
	148	*
	149	* Return :
	150	* 0 on success.
	151	* -EAGAIN if channel is disabled.
	152	* -ENOSPC if event size is too large for packet.
	153	* -ENOBUFS if there is currently not enough space in buffer for the event.
	154	* -EIO if data cannot be written into the buffer for any other reason.
	155	*/
	156
	157	static inline
4cfec15c	158	int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
e56bb47c MD	159	struct lttng_ust_lib_ring_buffer_ctx *ctx,
e56bb47c MD	160	void *client_ctx)
852c2936 MD	161	{
852c2936 MD	162	struct channel *chan = ctx->chan;
38fae1d3	163	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	164	struct lttng_ust_lib_ring_buffer *buf;
852c2936 MD	165	unsigned long o_begin, o_end, o_old;
	166	size_t before_hdr_pad = 0;
	167
f52a5702	168	if (caa_unlikely(uatomic_read(&chan->record_disabled)))
852c2936 MD	169	return -EAGAIN;
	170
	171	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
1d498196	172	buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
852c2936	173	else
1d498196	174	buf = shmp(handle, chan->backend.buf[0].shmp);
15500a1b MD	175	if (caa_unlikely(!buf))
15500a1b MD	176	return -EIO;
f52a5702	177	if (caa_unlikely(uatomic_read(&buf->record_disabled)))
852c2936 MD	178	return -EAGAIN;
	179	ctx->buf = buf;
	180
	181	/*
	182	* Perform retryable operations.
	183	*/
e56bb47c	184	if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, client_ctx, &o_begin,
852c2936 MD	185	&o_end, &o_old, &before_hdr_pad)))
	186	goto slow_path;
	187
b5a3dfa5	188	if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
852c2936 MD	189	!= o_old))
	190	goto slow_path;
	191
	192	/*
	193	* Atomically update last_tsc. This update races against concurrent
	194	* atomic updates, but the race will always cause supplementary full TSC
	195	* record headers, never the opposite (missing a full TSC record header
	196	* when it would be needed).
	197	*/
	198	save_last_tsc(config, ctx->buf, ctx->tsc);
	199
	200	/*
	201	* Push the reader if necessary
	202	*/
	203	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
	204
	205	/*
	206	* Clear noref flag for this subbuffer.
	207	*/
	208	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
1d498196	209	subbuf_index(o_end - 1, chan), handle);
852c2936 MD	210
	211	ctx->pre_offset = o_begin;
	212	ctx->buf_offset = o_begin + before_hdr_pad;
	213	return 0;
	214	slow_path:
e56bb47c	215	return lib_ring_buffer_reserve_slow(ctx, client_ctx);
852c2936 MD	216	}
	217
	218	/**
	219	* lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
	220	* @config: ring buffer instance configuration.
	221	* @buf: buffer
	222	* @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
	223	*
	224	* This operation is completely reentrant : can be called while tracing is
	225	* active with absolutely no lock held.
	226	*
	227	* Note, however, that as a v_cmpxchg is used for some atomic operations and
	228	* requires to be executed locally for per-CPU buffers, this function must be
	229	* called from the CPU which owns the buffer for a ACTIVE flush, with preemption
	230	* disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
	231	*/
	232	static inline
4cfec15c MD	233	void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	234	struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode,
38fae1d3	235	struct lttng_ust_shm_handle *handle)
852c2936	236	{
1d498196	237	lib_ring_buffer_switch_slow(buf, mode, handle);
852c2936 MD	238	}
	239
	240	/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */
	241
	242	/**
	243	* lib_ring_buffer_commit - Commit an record.
	244	* @config: ring buffer instance configuration.
	245	* @ctx: ring buffer context. (input arguments only)
	246	*
	247	* Atomic unordered slot commit. Increments the commit count in the
	248	* specified sub-buffer, and delivers it if necessary.
	249	*/
	250	static inline
4cfec15c MD	251	void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	252	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936 MD	253	{
852c2936 MD	254	struct channel *chan = ctx->chan;
38fae1d3	255	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	256	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	257	unsigned long offset_end = ctx->buf_offset;
	258	unsigned long endidx = subbuf_index(offset_end - 1, chan);
	259	unsigned long commit_count;
d2fe4771 MD	260	struct commit_counters_hot *cc_hot = shmp_index(handle,
d2fe4771 MD	261	buf->commit_hot, endidx);
852c2936	262
15500a1b MD	263	if (caa_unlikely(!cc_hot))
	264	return;
	265
852c2936 MD	266	/*
	267	* Must count record before incrementing the commit count.
	268	*/
15500a1b	269	subbuffer_count_record(config, ctx, &buf->backend, endidx, handle);
852c2936 MD	270
	271	/*
	272	* Order all writes to buffer before the commit count update that will
	273	* determine that the subbuffer is full.
	274	*/
9f3fdbc6	275	cmm_smp_wmb();
852c2936	276
d2fe4771	277	v_add(config, ctx->slot_size, &cc_hot->cc);
852c2936 MD	278
	279	/*
	280	* commit count read can race with concurrent OOO commit count updates.
	281	* This is only needed for lib_ring_buffer_check_deliver (for
	282	* non-polling delivery only) and for
	283	* lib_ring_buffer_write_commit_counter. The race can only cause the
	284	* counter to be read with the same value more than once, which could
	285	* cause :
	286	* - Multiple delivery for the same sub-buffer (which is handled
	287	* gracefully by the reader code) if the value is for a full
	288	* sub-buffer. It's important that we can never miss a sub-buffer
	289	* delivery. Re-reading the value after the v_add ensures this.
	290	* - Reading a commit_count with a higher value that what was actually
	291	* added to it for the lib_ring_buffer_write_commit_counter call
	292	* (again caused by a concurrent committer). It does not matter,
	293	* because this function is interested in the fact that the commit
	294	* count reaches back the reserve offset for a specific sub-buffer,
	295	* which is completely independent of the order.
	296	*/
d2fe4771	297	commit_count = v_read(config, &cc_hot->cc);
852c2936 MD	298
852c2936 MD	299	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
1b7b0501	300	commit_count, endidx, handle, ctx->tsc);
852c2936 MD	301	/*
	302	* Update used size at each commit. It's needed only for extracting
	303	* ring_buffer buffers from vmcore, after crash.
	304	*/
d2fe4771 MD	305	lib_ring_buffer_write_commit_counter(config, buf, chan,
d2fe4771 MD	306	offset_end, commit_count, handle, cc_hot);
852c2936 MD	307	}
	308
	309	/**
	310	* lib_ring_buffer_try_discard_reserve - Try discarding a record.
	311	* @config: ring buffer instance configuration.
	312	* @ctx: ring buffer context. (input arguments only)
	313	*
	314	* Only succeeds if no other record has been written after the record to
	315	* discard. If discard fails, the record must be committed to the buffer.
	316	*
	317	* Returns 0 upon success, -EPERM if the record cannot be discarded.
	318	*/
	319	static inline
4cfec15c MD	320	int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	321	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936	322	{
4cfec15c	323	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	324	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;
	325
	326	/*
	327	* We need to ensure that if the cmpxchg succeeds and discards the
	328	* record, the next record will record a full TSC, because it cannot
	329	* rely on the last_tsc associated with the discarded record to detect
	330	* overflows. The only way to ensure this is to set the last_tsc to 0
	331	* (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	332	* timestamp in the next record.
	333	*
	334	* Note: if discard fails, we must leave the TSC in the record header.
	335	* It is needed to keep track of TSC overflows for the following
	336	* records.
	337	*/
	338	save_last_tsc(config, buf, 0ULL);
	339
b5a3dfa5	340	if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
852c2936 MD	341	!= end_offset))
	342	return -EPERM;
	343	else
	344	return 0;
	345	}
	346
	347	static inline
4cfec15c	348	void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	349	struct channel *chan)
852c2936 MD	350	{
9f3fdbc6	351	uatomic_inc(&chan->record_disabled);
852c2936 MD	352	}
	353
	354	static inline
4cfec15c	355	void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	356	struct channel *chan)
852c2936 MD	357	{
9f3fdbc6	358	uatomic_dec(&chan->record_disabled);
852c2936 MD	359	}
	360
	361	static inline
4cfec15c MD	362	void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	363	struct lttng_ust_lib_ring_buffer *buf)
852c2936	364	{
9f3fdbc6	365	uatomic_inc(&buf->record_disabled);
852c2936 MD	366	}
	367
	368	static inline
4cfec15c MD	369	void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	370	struct lttng_ust_lib_ring_buffer *buf)
852c2936	371	{
9f3fdbc6	372	uatomic_dec(&buf->record_disabled);
852c2936 MD	373	}
852c2936 MD	374
e92f3e28	375	#endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */