[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>
#include "rseq.h"

static inline
int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
{
	return lttng_ust_get_cpu();
}

/**
 * lib_ring_buffer_begin - 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_begin(const struct lttng_ust_lib_ring_buffer_config *config)
{
	int nesting;

	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;
	}
	return 0;
}

/**
 * lib_ring_buffer_end - Follows ring buffer reserve/commit.
 */
static inline
void lib_ring_buffer_end(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 (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, &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;
	struct commit_counters_hot *cc_hot = shmp_index(handle,
						buf->commit_hot, endidx);
	struct lttng_rseq_state rseq_state;

	if (caa_likely(ctx->ctx_len
			>= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) {
		rseq_state = ctx->rseq_state;
	} else {
		rseq_state.cpu_id = -2;
	}

	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();

	if (caa_likely(rseq_state.cpu_id >= 0)) {
		unsigned long newv;

		newv = cc_hot->cc_rseq + ctx->slot_size;
		if (caa_likely(__rseq_finish(NULL, 0, NULL, NULL, 0,
				(intptr_t *)&cc_hot->cc_rseq,
				(intptr_t) newv,
				rseq_state, RSEQ_FINISH_SINGLE, false)))
			goto add_done;
	}
	v_add(config, ctx->slot_size, &cc_hot->cc);
add_done:

	/*
	 * 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);
	commit_count += cc_hot->cc_rseq;

	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
4931a13e	33	#include "frontend.h"
9f3fdbc6 MD	34	#include <urcu-bp.h>
9f3fdbc6 MD	35	#include <urcu/compiler.h>
3ea36dea	36	#include "rseq.h"
852c2936	37
26cc635c MD	38	static inline
	39	int lib_ring_buffer_get_cpu(const struct lttng_ust_lib_ring_buffer_config *config)
	40	{
	41	return lttng_ust_get_cpu();
	42	}
	43
852c2936	44	/**
26cc635c	45	* lib_ring_buffer_begin - Precedes ring buffer reserve/commit.
852c2936	46	*
36cb884c MD	47	* Keeps a ring buffer nesting count as supplementary safety net to
	48	* ensure tracer client code will never trigger an endless recursion.
	49	* Returns the processor ID on success, -EPERM on failure (nesting count
	50	* too high).
852c2936 MD	51	*
	52	* asm volatile and "memory" clobber prevent the compiler from moving
	53	* instructions out of the ring buffer nesting count. This is required to ensure
	54	* that probe side-effects which can cause recursion (e.g. unforeseen traps,
	55	* divisions by 0, ...) are triggered within the incremented nesting count
	56	* section.
	57	*/
	58	static inline
26cc635c	59	int lib_ring_buffer_begin(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936	60	{
26cc635c	61	int nesting;
852c2936	62
8c90a710	63	nesting = ++URCU_TLS(lib_ring_buffer_nesting);
9f3fdbc6	64	cmm_barrier();
852c2936	65
b5a3dfa5	66	if (caa_unlikely(nesting > 4)) {
852c2936	67	WARN_ON_ONCE(1);
8c90a710	68	URCU_TLS(lib_ring_buffer_nesting)--;
852c2936	69	return -EPERM;
26cc635c MD	70	}
26cc635c MD	71	return 0;
852c2936 MD	72	}
	73
	74	/**
26cc635c	75	* lib_ring_buffer_end - Follows ring buffer reserve/commit.
852c2936 MD	76	*/
852c2936 MD	77	static inline
26cc635c	78	void lib_ring_buffer_end(const struct lttng_ust_lib_ring_buffer_config *config)
852c2936	79	{
9f3fdbc6	80	cmm_barrier();
8c90a710	81	URCU_TLS(lib_ring_buffer_nesting)--; /* TLS */
852c2936 MD	82	}
	83
	84	/*
	85	* lib_ring_buffer_try_reserve is called by lib_ring_buffer_reserve(). It is not
	86	* part of the API per se.
	87	*
	88	* returns 0 if reserve ok, or 1 if the slow path must be taken.
	89	*/
	90	static inline
4cfec15c MD	91	int lib_ring_buffer_try_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	92	struct lttng_ust_lib_ring_buffer_ctx *ctx,
852c2936 MD	93	unsigned long o_begin, unsigned long o_end,
	94	unsigned long o_old, size_t before_hdr_pad)
	95	{
	96	struct channel *chan = ctx->chan;
4cfec15c	97	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	98	*o_begin = v_read(config, &buf->offset);
	99	o_old = o_begin;
	100
	101	ctx->tsc = lib_ring_buffer_clock_read(chan);
	102	if ((int64_t) ctx->tsc == -EIO)
	103	return 1;
	104
	105	/*
	106	* Prefetch cacheline for read because we have to read the previous
	107	* commit counter to increment it and commit seq value to compare it to
	108	* the commit counter.
	109	*/
9f3fdbc6	110	//prefetch(&buf->commit_hot[subbuf_index(*o_begin, chan)]);
852c2936 MD	111
	112	if (last_tsc_overflow(config, buf, ctx->tsc))
	113	ctx->rflags \|= RING_BUFFER_RFLAG_FULL_TSC;
	114
b5a3dfa5	115	if (caa_unlikely(subbuf_offset(*o_begin, chan) == 0))
852c2936 MD	116	return 1;
	117
	118	ctx->slot_size = record_header_size(config, chan, *o_begin,
	119	before_hdr_pad, ctx);
	120	ctx->slot_size +=
	121	lib_ring_buffer_align(*o_begin + ctx->slot_size,
	122	ctx->largest_align) + ctx->data_size;
b5a3dfa5	123	if (caa_unlikely((subbuf_offset(*o_begin, chan) + ctx->slot_size)
852c2936 MD	124	> chan->backend.subbuf_size))
	125	return 1;
	126
	127	/*
	128	* Record fits in the current buffer and we are not on a switch
	129	* boundary. It's safe to write.
	130	*/
	131	o_end = o_begin + ctx->slot_size;
1ad21f70 MD	132
	133	if (caa_unlikely((subbuf_offset(*o_end, chan)) == 0))
	134	/*
	135	* The offset_end will fall at the very beginning of the next
	136	* subbuffer.
	137	*/
	138	return 1;
	139
852c2936 MD	140	return 0;
	141	}
	142
	143	/**
	144	* lib_ring_buffer_reserve - Reserve space in a ring buffer.
	145	* @config: ring buffer instance configuration.
	146	* @ctx: ring buffer context. (input and output) Must be already initialized.
	147	*
	148	* Atomic wait-free slot reservation. The reserved space starts at the context
	149	* "pre_offset". Its length is "slot_size". The associated time-stamp is "tsc".
	150	*
	151	* Return :
	152	* 0 on success.
	153	* -EAGAIN if channel is disabled.
	154	* -ENOSPC if event size is too large for packet.
	155	* -ENOBUFS if there is currently not enough space in buffer for the event.
	156	* -EIO if data cannot be written into the buffer for any other reason.
	157	*/
	158
	159	static inline
4cfec15c MD	160	int lib_ring_buffer_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	161	struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936 MD	162	{
852c2936 MD	163	struct channel *chan = ctx->chan;
38fae1d3	164	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	165	struct lttng_ust_lib_ring_buffer *buf;
852c2936 MD	166	unsigned long o_begin, o_end, o_old;
	167	size_t before_hdr_pad = 0;
	168
f52a5702	169	if (caa_unlikely(uatomic_read(&chan->record_disabled)))
852c2936 MD	170	return -EAGAIN;
	171
	172	if (config->alloc == RING_BUFFER_ALLOC_PER_CPU)
1d498196	173	buf = shmp(handle, chan->backend.buf[ctx->cpu].shmp);
852c2936	174	else
1d498196	175	buf = shmp(handle, chan->backend.buf[0].shmp);
15500a1b MD	176	if (caa_unlikely(!buf))
15500a1b MD	177	return -EIO;
f52a5702	178	if (caa_unlikely(uatomic_read(&buf->record_disabled)))
852c2936 MD	179	return -EAGAIN;
	180	ctx->buf = buf;
	181
	182	/*
	183	* Perform retryable operations.
	184	*/
b5a3dfa5	185	if (caa_unlikely(lib_ring_buffer_try_reserve(config, ctx, &o_begin,
852c2936 MD	186	&o_end, &o_old, &before_hdr_pad)))
	187	goto slow_path;
	188
b5a3dfa5	189	if (caa_unlikely(v_cmpxchg(config, &ctx->buf->offset, o_old, o_end)
852c2936 MD	190	!= o_old))
	191	goto slow_path;
	192
	193	/*
	194	* Atomically update last_tsc. This update races against concurrent
	195	* atomic updates, but the race will always cause supplementary full TSC
	196	* record headers, never the opposite (missing a full TSC record header
	197	* when it would be needed).
	198	*/
	199	save_last_tsc(config, ctx->buf, ctx->tsc);
	200
	201	/*
	202	* Push the reader if necessary
	203	*/
	204	lib_ring_buffer_reserve_push_reader(ctx->buf, chan, o_end - 1);
	205
	206	/*
	207	* Clear noref flag for this subbuffer.
	208	*/
	209	lib_ring_buffer_clear_noref(config, &ctx->buf->backend,
1d498196	210	subbuf_index(o_end - 1, chan), handle);
852c2936 MD	211
	212	ctx->pre_offset = o_begin;
	213	ctx->buf_offset = o_begin + before_hdr_pad;
	214	return 0;
	215	slow_path:
	216	return lib_ring_buffer_reserve_slow(ctx);
	217	}
	218
	219	/**
	220	* lib_ring_buffer_switch - Perform a sub-buffer switch for a per-cpu buffer.
	221	* @config: ring buffer instance configuration.
	222	* @buf: buffer
	223	* @mode: buffer switch mode (SWITCH_ACTIVE or SWITCH_FLUSH)
	224	*
	225	* This operation is completely reentrant : can be called while tracing is
	226	* active with absolutely no lock held.
	227	*
	228	* Note, however, that as a v_cmpxchg is used for some atomic operations and
	229	* requires to be executed locally for per-CPU buffers, this function must be
	230	* called from the CPU which owns the buffer for a ACTIVE flush, with preemption
	231	* disabled, for RING_BUFFER_SYNC_PER_CPU configuration.
	232	*/
	233	static inline
4cfec15c MD	234	void lib_ring_buffer_switch(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	235	struct lttng_ust_lib_ring_buffer *buf, enum switch_mode mode,
38fae1d3	236	struct lttng_ust_shm_handle *handle)
852c2936	237	{
1d498196	238	lib_ring_buffer_switch_slow(buf, mode, handle);
852c2936 MD	239	}
	240
	241	/* See ring_buffer_frontend_api.h for lib_ring_buffer_reserve(). */
	242
	243	/**
	244	* lib_ring_buffer_commit - Commit an record.
	245	* @config: ring buffer instance configuration.
	246	* @ctx: ring buffer context. (input arguments only)
	247	*
	248	* Atomic unordered slot commit. Increments the commit count in the
	249	* specified sub-buffer, and delivers it if necessary.
	250	*/
	251	static inline
4cfec15c MD	252	void lib_ring_buffer_commit(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	253	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936 MD	254	{
852c2936 MD	255	struct channel *chan = ctx->chan;
38fae1d3	256	struct lttng_ust_shm_handle *handle = ctx->handle;
4cfec15c	257	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	258	unsigned long offset_end = ctx->buf_offset;
	259	unsigned long endidx = subbuf_index(offset_end - 1, chan);
	260	unsigned long commit_count;
d2fe4771 MD	261	struct commit_counters_hot *cc_hot = shmp_index(handle,
d2fe4771 MD	262	buf->commit_hot, endidx);
3ea36dea MD	263	struct lttng_rseq_state rseq_state;
	264
	265	if (caa_likely(ctx->ctx_len
	266	>= sizeof(struct lttng_ust_lib_ring_buffer_ctx))) {
	267	rseq_state = ctx->rseq_state;
	268	} else {
	269	rseq_state.cpu_id = -2;
	270	}
852c2936	271
15500a1b MD	272	if (caa_unlikely(!cc_hot))
	273	return;
	274
852c2936 MD	275	/*
	276	* Must count record before incrementing the commit count.
	277	*/
15500a1b	278	subbuffer_count_record(config, ctx, &buf->backend, endidx, handle);
852c2936 MD	279
	280	/*
	281	* Order all writes to buffer before the commit count update that will
	282	* determine that the subbuffer is full.
	283	*/
9f3fdbc6	284	cmm_smp_wmb();
852c2936	285
3ea36dea MD	286	if (caa_likely(rseq_state.cpu_id >= 0)) {
	287	unsigned long newv;
	288
	289	newv = cc_hot->cc_rseq + ctx->slot_size;
	290	if (caa_likely(__rseq_finish(NULL, 0, NULL, NULL, 0,
	291	(intptr_t *)&cc_hot->cc_rseq,
	292	(intptr_t) newv,
	293	rseq_state, RSEQ_FINISH_SINGLE, false)))
	294	goto add_done;
	295	}
d2fe4771	296	v_add(config, ctx->slot_size, &cc_hot->cc);
3ea36dea	297	add_done:
852c2936 MD	298
	299	/*
	300	* commit count read can race with concurrent OOO commit count updates.
	301	* This is only needed for lib_ring_buffer_check_deliver (for
	302	* non-polling delivery only) and for
	303	* lib_ring_buffer_write_commit_counter. The race can only cause the
	304	* counter to be read with the same value more than once, which could
	305	* cause :
	306	* - Multiple delivery for the same sub-buffer (which is handled
	307	* gracefully by the reader code) if the value is for a full
	308	* sub-buffer. It's important that we can never miss a sub-buffer
	309	* delivery. Re-reading the value after the v_add ensures this.
	310	* - Reading a commit_count with a higher value that what was actually
	311	* added to it for the lib_ring_buffer_write_commit_counter call
	312	* (again caused by a concurrent committer). It does not matter,
	313	* because this function is interested in the fact that the commit
	314	* count reaches back the reserve offset for a specific sub-buffer,
	315	* which is completely independent of the order.
	316	*/
d2fe4771	317	commit_count = v_read(config, &cc_hot->cc);
3ea36dea	318	commit_count += cc_hot->cc_rseq;
852c2936 MD	319
852c2936 MD	320	lib_ring_buffer_check_deliver(config, buf, chan, offset_end - 1,
1b7b0501	321	commit_count, endidx, handle, ctx->tsc);
852c2936 MD	322	/*
	323	* Update used size at each commit. It's needed only for extracting
	324	* ring_buffer buffers from vmcore, after crash.
	325	*/
d2fe4771 MD	326	lib_ring_buffer_write_commit_counter(config, buf, chan,
d2fe4771 MD	327	offset_end, commit_count, handle, cc_hot);
852c2936 MD	328	}
	329
	330	/**
	331	* lib_ring_buffer_try_discard_reserve - Try discarding a record.
	332	* @config: ring buffer instance configuration.
	333	* @ctx: ring buffer context. (input arguments only)
	334	*
	335	* Only succeeds if no other record has been written after the record to
	336	* discard. If discard fails, the record must be committed to the buffer.
	337	*
	338	* Returns 0 upon success, -EPERM if the record cannot be discarded.
	339	*/
	340	static inline
4cfec15c MD	341	int lib_ring_buffer_try_discard_reserve(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	342	const struct lttng_ust_lib_ring_buffer_ctx *ctx)
852c2936	343	{
4cfec15c	344	struct lttng_ust_lib_ring_buffer *buf = ctx->buf;
852c2936 MD	345	unsigned long end_offset = ctx->pre_offset + ctx->slot_size;
	346
	347	/*
	348	* We need to ensure that if the cmpxchg succeeds and discards the
	349	* record, the next record will record a full TSC, because it cannot
	350	* rely on the last_tsc associated with the discarded record to detect
	351	* overflows. The only way to ensure this is to set the last_tsc to 0
	352	* (assuming no 64-bit TSC overflow), which forces to write a 64-bit
	353	* timestamp in the next record.
	354	*
	355	* Note: if discard fails, we must leave the TSC in the record header.
	356	* It is needed to keep track of TSC overflows for the following
	357	* records.
	358	*/
	359	save_last_tsc(config, buf, 0ULL);
	360
b5a3dfa5	361	if (caa_likely(v_cmpxchg(config, &buf->offset, end_offset, ctx->pre_offset)
852c2936 MD	362	!= end_offset))
	363	return -EPERM;
	364	else
	365	return 0;
	366	}
	367
	368	static inline
4cfec15c	369	void channel_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	370	struct channel *chan)
852c2936 MD	371	{
9f3fdbc6	372	uatomic_inc(&chan->record_disabled);
852c2936 MD	373	}
	374
	375	static inline
4cfec15c	376	void channel_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	377	struct channel *chan)
852c2936 MD	378	{
9f3fdbc6	379	uatomic_dec(&chan->record_disabled);
852c2936 MD	380	}
	381
	382	static inline
4cfec15c MD	383	void lib_ring_buffer_record_disable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	384	struct lttng_ust_lib_ring_buffer *buf)
852c2936	385	{
9f3fdbc6	386	uatomic_inc(&buf->record_disabled);
852c2936 MD	387	}
	388
	389	static inline
4cfec15c MD	390	void lib_ring_buffer_record_enable(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	391	struct lttng_ust_lib_ring_buffer *buf)
852c2936	392	{
9f3fdbc6	393	uatomic_dec(&buf->record_disabled);
852c2936 MD	394	}
852c2936 MD	395
e92f3e28	396	#endif /* _LTTNG_RING_BUFFER_FRONTEND_API_H */