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

/*
 * SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
 *
 * Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Ring Buffer Library Synchronization Header (internal helpers).
 *
 * See ring_buffer_frontend.c for more information on wait-free algorithms.
 */

#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H

#include <urcu/compiler.h>
#include <urcu/tls-compat.h>
#include <signal.h>
#include <stdint.h>
#include <pthread.h>

#include <lttng/ringbuffer-config.h>
#include "backend_types.h"
#include "frontend_types.h"
#include "shm.h"

/* Buffer offset macros */

/* buf_trunc mask selects only the buffer number. */
static inline
unsigned long buf_trunc(unsigned long offset, struct channel *chan)
{
	return offset & ~(chan->backend.buf_size - 1);

}

/* Select the buffer number value (counter). */
static inline
unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
{
	return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
}

/* buf_offset mask selects only the offset within the current buffer. */
static inline
unsigned long buf_offset(unsigned long offset, struct channel *chan)
{
	return offset & (chan->backend.buf_size - 1);
}

/* subbuf_offset mask selects the offset within the current subbuffer. */
static inline
unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
{
	return offset & (chan->backend.subbuf_size - 1);
}

/* subbuf_trunc mask selects the subbuffer number. */
static inline
unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
{
	return offset & ~(chan->backend.subbuf_size - 1);
}

/* subbuf_align aligns the offset to the next subbuffer. */
static inline
unsigned long subbuf_align(unsigned long offset, struct channel *chan)
{
	return (offset + chan->backend.subbuf_size)
	       & ~(chan->backend.subbuf_size - 1);
}

/* subbuf_index returns the index of the current subbuffer within the buffer. */
static inline
unsigned long subbuf_index(unsigned long offset, struct channel *chan)
{
	return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
}

/*
 * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
 * bits from the last TSC read. When overflows are detected, the full 64-bit
 * timestamp counter should be written in the record header. Reads and writes
 * last_tsc atomically.
 */

#if (CAA_BITS_PER_LONG == 32)
static inline
void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
		   struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
{
	if (config->tsc_bits == 0 || config->tsc_bits == 64)
		return;

	/*
	 * Ensure the compiler performs this update in a single instruction.
	 */
	v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
}

static inline
int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
		      struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
{
	unsigned long tsc_shifted;

	if (config->tsc_bits == 0 || config->tsc_bits == 64)
		return 0;

	tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
	if (caa_unlikely(tsc_shifted
		     - (unsigned long)v_read(config, &buf->last_tsc)))
		return 1;
	else
		return 0;
}
#else
static inline
void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
		   struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
{
	if (config->tsc_bits == 0 || config->tsc_bits == 64)
		return;

	v_set(config, &buf->last_tsc, (unsigned long)tsc);
}

static inline
int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
		      struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
{
	if (config->tsc_bits == 0 || config->tsc_bits == 64)
		return 0;

	if (caa_unlikely((tsc - v_read(config, &buf->last_tsc))
		     >> config->tsc_bits))
		return 1;
	else
		return 0;
}
#endif

__attribute__((visibility("hidden")))
extern
int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
		void *client_ctx);

__attribute__((visibility("hidden")))
extern
void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
				 enum switch_mode mode,
				 struct lttng_ust_shm_handle *handle);

__attribute__((visibility("hidden")))
void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
				   struct lttng_ust_lib_ring_buffer *buf,
			           struct channel *chan,
			           unsigned long offset,
				   unsigned long commit_count,
			           unsigned long idx,
				   struct lttng_ust_shm_handle *handle,
				   uint64_t tsc);

/* Buffer write helpers */

static inline
void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
					 struct channel *chan,
					 unsigned long offset)
{
	unsigned long consumed_old, consumed_new;

	do {
		consumed_old = uatomic_read(&buf->consumed);
		/*
		 * If buffer is in overwrite mode, push the reader consumed
		 * count if the write position has reached it and we are not
		 * at the first iteration (don't push the reader farther than
		 * the writer). This operation can be done concurrently by many
		 * writers in the same buffer, the writer being at the farthest
		 * write position sub-buffer index in the buffer being the one
		 * which will win this loop.
		 */
		if (caa_unlikely(subbuf_trunc(offset, chan)
			      - subbuf_trunc(consumed_old, chan)
			     >= chan->backend.buf_size))
			consumed_new = subbuf_align(consumed_old, chan);
		else
			return;
	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
					      consumed_new) != consumed_old));
}

/*
 * Move consumed position to the beginning of subbuffer in which the
 * write offset is. Should only be used on ring buffers that are not
 * actively being written into, because clear_reader does not take into
 * account the commit counters when moving the consumed position, which
 * can make concurrent trace producers or consumers observe consumed
 * position further than the write offset, which breaks ring buffer
 * algorithm guarantees.
 */
static inline
void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
				  struct lttng_ust_shm_handle *handle)
{
	struct channel *chan;
	const struct lttng_ust_lib_ring_buffer_config *config;
	unsigned long offset, consumed_old, consumed_new;

	chan = shmp(handle, buf->backend.chan);
	if (!chan)
		return;
	config = &chan->backend.config;

	do {
		offset = v_read(config, &buf->offset);
		consumed_old = uatomic_read(&buf->consumed);
		CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
				- subbuf_trunc(consumed_old, chan))
				< 0);
		consumed_new = subbuf_trunc(offset, chan);
	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
					      consumed_new) != consumed_old));
}

static inline
int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
				 struct lttng_ust_lib_ring_buffer *buf,
				 struct channel *chan)
{
	return !!subbuf_offset(v_read(config, &buf->offset), chan);
}

static inline
unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
					    struct lttng_ust_lib_ring_buffer *buf,
					    unsigned long idx,
					    struct lttng_ust_shm_handle *handle)
{
	return subbuffer_get_data_size(config, &buf->backend, idx, handle);
}

/*
 * Check if all space reservation in a buffer have been committed. This helps
 * knowing if an execution context is nested (for per-cpu buffers only).
 * This is a very specific ftrace use-case, so we keep this as "internal" API.
 */
static inline
int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config *config,
				      struct lttng_ust_lib_ring_buffer *buf,
				      struct channel *chan,
				      struct lttng_ust_shm_handle *handle)
{
	unsigned long offset, idx, commit_count;
	struct commit_counters_hot *cc_hot;

	CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
	CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);

	/*
	 * Read offset and commit count in a loop so they are both read
	 * atomically wrt interrupts. By deal with interrupt concurrency by
	 * restarting both reads if the offset has been pushed. Note that given
	 * we only have to deal with interrupt concurrency here, an interrupt
	 * modifying the commit count will also modify "offset", so it is safe
	 * to only check for offset modifications.
	 */
	do {
		offset = v_read(config, &buf->offset);
		idx = subbuf_index(offset, chan);
		cc_hot = shmp_index(handle, buf->commit_hot, idx);
		if (caa_unlikely(!cc_hot))
			return 0;
		commit_count = v_read(config, &cc_hot->cc);
	} while (offset != v_read(config, &buf->offset));

	return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
		     - (commit_count & chan->commit_count_mask) == 0);
}

/*
 * Receive end of subbuffer TSC as parameter. It has been read in the
 * space reservation loop of either reserve or switch, which ensures it
 * progresses monotonically with event records in the buffer. Therefore,
 * it ensures that the end timestamp of a subbuffer is <= begin
 * timestamp of the following subbuffers.
 */
static inline
void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
				   struct lttng_ust_lib_ring_buffer *buf,
			           struct channel *chan,
			           unsigned long offset,
				   unsigned long commit_count,
			           unsigned long idx,
				   struct lttng_ust_shm_handle *handle,
				   uint64_t tsc)
{
	unsigned long old_commit_count = commit_count
					 - chan->backend.subbuf_size;

	/* Check if all commits have been done */
	if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
		     - (old_commit_count & chan->commit_count_mask) == 0))
		lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
			commit_count, idx, handle, tsc);
}

/*
 * lib_ring_buffer_write_commit_counter
 *
 * For flight recording. must be called after commit.
 * This function increments the subbuffer's commit_seq counter each time the
 * commit count reaches back the reserve offset (modulo subbuffer size). It is
 * useful for crash dump.
 */
static inline
void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config,
					  struct lttng_ust_lib_ring_buffer *buf,
				          struct channel *chan,
				          unsigned long buf_offset,
				          unsigned long commit_count,
					  struct lttng_ust_shm_handle *handle,
					  struct commit_counters_hot *cc_hot)
{
	unsigned long commit_seq_old;

	if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
		return;

	/*
	 * subbuf_offset includes commit_count_mask. We can simply
	 * compare the offsets within the subbuffer without caring about
	 * buffer full/empty mismatch because offset is never zero here
	 * (subbuffer header and record headers have non-zero length).
	 */
	if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
		return;

	commit_seq_old = v_read(config, &cc_hot->seq);
	if (caa_likely((long) (commit_seq_old - commit_count) < 0))
		v_set(config, &cc_hot->seq, commit_count);
}

__attribute__((visibility("hidden")))
extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf,
				  struct channel_backend *chanb, int cpu,
				  struct lttng_ust_shm_handle *handle,
				  struct shm_object *shmobj);

__attribute__((visibility("hidden")))
extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer *buf,
				 struct lttng_ust_shm_handle *handle);

/* Keep track of trap nesting inside ring buffer code */
__attribute__((visibility("hidden")))
extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting);

#endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */
Commit	Line	Data
852c2936	1	/*
c0c0989a	2	* SPDX-License-Identifier: (LGPL-2.1-only or GPL-2.0-only)
852c2936	3	*
e92f3e28 MD	4	* Copyright (C) 2005-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
e92f3e28 MD	5	*
c0c0989a	6	* Ring Buffer Library Synchronization Header (internal helpers).
852c2936 MD	7	*
852c2936 MD	8	* See ring_buffer_frontend.c for more information on wait-free algorithms.
852c2936 MD	9	*/
852c2936 MD	10
c0c0989a MJ	11	#ifndef _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
	12	#define _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H
	13
14641deb	14	#include <urcu/compiler.h>
8c90a710	15	#include <urcu/tls-compat.h>
2c44f5b9	16	#include <signal.h>
fb31eb73	17	#include <stdint.h>
2c44f5b9	18	#include <pthread.h>
14641deb	19
4318ae1b	20	#include <lttng/ringbuffer-config.h>
4931a13e MD	21	#include "backend_types.h"
4931a13e MD	22	#include "frontend_types.h"
a6352fd4	23	#include "shm.h"
852c2936 MD	24
	25	/* Buffer offset macros */
	26
	27	/* buf_trunc mask selects only the buffer number. */
	28	static inline
	29	unsigned long buf_trunc(unsigned long offset, struct channel *chan)
	30	{
	31	return offset & ~(chan->backend.buf_size - 1);
	32
	33	}
	34
	35	/* Select the buffer number value (counter). */
	36	static inline
	37	unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
	38	{
	39	return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
	40	}
	41
	42	/* buf_offset mask selects only the offset within the current buffer. */
	43	static inline
	44	unsigned long buf_offset(unsigned long offset, struct channel *chan)
	45	{
	46	return offset & (chan->backend.buf_size - 1);
	47	}
	48
	49	/* subbuf_offset mask selects the offset within the current subbuffer. */
	50	static inline
	51	unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
	52	{
	53	return offset & (chan->backend.subbuf_size - 1);
	54	}
	55
	56	/* subbuf_trunc mask selects the subbuffer number. */
	57	static inline
	58	unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
	59	{
	60	return offset & ~(chan->backend.subbuf_size - 1);
	61	}
	62
	63	/* subbuf_align aligns the offset to the next subbuffer. */
	64	static inline
	65	unsigned long subbuf_align(unsigned long offset, struct channel *chan)
	66	{
	67	return (offset + chan->backend.subbuf_size)
	68	& ~(chan->backend.subbuf_size - 1);
	69	}
	70
	71	/* subbuf_index returns the index of the current subbuffer within the buffer. */
	72	static inline
	73	unsigned long subbuf_index(unsigned long offset, struct channel *chan)
	74	{
	75	return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
	76	}
	77
	78	/*
	79	* Last TSC comparison functions. Check if the current TSC overflows tsc_bits
	80	* bits from the last TSC read. When overflows are detected, the full 64-bit
	81	* timestamp counter should be written in the record header. Reads and writes
	82	* last_tsc atomically.
	83	*/
	84
14641deb	85	#if (CAA_BITS_PER_LONG == 32)
852c2936	86	static inline
4cfec15c	87	void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	88	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	89	{
	90	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	91	return;
	92
	93	/*
	94	* Ensure the compiler performs this update in a single instruction.
	95	*/
	96	v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
	97	}
	98
	99	static inline
4cfec15c	100	int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	101	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	102	{
	103	unsigned long tsc_shifted;
	104
	105	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	106	return 0;
	107
	108	tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
b5a3dfa5	109	if (caa_unlikely(tsc_shifted
852c2936 MD	110	- (unsigned long)v_read(config, &buf->last_tsc)))
	111	return 1;
	112	else
	113	return 0;
	114	}
	115	#else
	116	static inline
4cfec15c	117	void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	118	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	119	{
	120	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	121	return;
	122
	123	v_set(config, &buf->last_tsc, (unsigned long)tsc);
	124	}
	125
	126	static inline
4cfec15c	127	int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	128	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	129	{
	130	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	131	return 0;
	132
b5a3dfa5	133	if (caa_unlikely((tsc - v_read(config, &buf->last_tsc))
852c2936 MD	134	>> config->tsc_bits))
	135	return 1;
	136	else
	137	return 0;
	138	}
	139	#endif
	140
ddabe860	141	__attribute__((visibility("hidden")))
852c2936	142	extern
e56bb47c MD	143	int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
e56bb47c MD	144	void *client_ctx);
852c2936	145
ddabe860	146	__attribute__((visibility("hidden")))
852c2936	147	extern
4cfec15c	148	void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
1d498196	149	enum switch_mode mode,
38fae1d3	150	struct lttng_ust_shm_handle *handle);
852c2936	151
ddabe860	152	__attribute__((visibility("hidden")))
b07cd987 MD	153	void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
	154	struct lttng_ust_lib_ring_buffer *buf,
	155	struct channel *chan,
	156	unsigned long offset,
	157	unsigned long commit_count,
	158	unsigned long idx,
	159	struct lttng_ust_shm_handle *handle,
	160	uint64_t tsc);
	161
852c2936 MD	162	/* Buffer write helpers */
	163
	164	static inline
4cfec15c	165	void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	166	struct channel *chan,
	167	unsigned long offset)
	168	{
	169	unsigned long consumed_old, consumed_new;
	170
	171	do {
14641deb	172	consumed_old = uatomic_read(&buf->consumed);
852c2936 MD	173	/*
	174	* If buffer is in overwrite mode, push the reader consumed
	175	* count if the write position has reached it and we are not
	176	* at the first iteration (don't push the reader farther than
	177	* the writer). This operation can be done concurrently by many
	178	* writers in the same buffer, the writer being at the farthest
	179	* write position sub-buffer index in the buffer being the one
	180	* which will win this loop.
	181	*/
b5a3dfa5	182	if (caa_unlikely(subbuf_trunc(offset, chan)
852c2936 MD	183	- subbuf_trunc(consumed_old, chan)
	184	>= chan->backend.buf_size))
	185	consumed_new = subbuf_align(consumed_old, chan);
	186	else
	187	return;
b5a3dfa5	188	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
852c2936 MD	189	consumed_new) != consumed_old));
	190	}
	191
4c742ffd MD	192	/*
	193	* Move consumed position to the beginning of subbuffer in which the
	194	* write offset is. Should only be used on ring buffers that are not
	195	* actively being written into, because clear_reader does not take into
	196	* account the commit counters when moving the consumed position, which
	197	* can make concurrent trace producers or consumers observe consumed
	198	* position further than the write offset, which breaks ring buffer
	199	* algorithm guarantees.
	200	*/
beca55a1 MD	201	static inline
	202	void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
	203	struct lttng_ust_shm_handle *handle)
	204	{
	205	struct channel *chan;
	206	const struct lttng_ust_lib_ring_buffer_config *config;
	207	unsigned long offset, consumed_old, consumed_new;
	208
	209	chan = shmp(handle, buf->backend.chan);
	210	if (!chan)
	211	return;
	212	config = &chan->backend.config;
	213
	214	do {
	215	offset = v_read(config, &buf->offset);
	216	consumed_old = uatomic_read(&buf->consumed);
4c742ffd MD	217	CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
	218	- subbuf_trunc(consumed_old, chan))
	219	< 0);
	220	consumed_new = subbuf_trunc(offset, chan);
beca55a1 MD	221	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
	222	consumed_new) != consumed_old));
	223	}
	224
852c2936	225	static inline
4cfec15c MD	226	int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	227	struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	228	struct channel *chan)
	229	{
	230	return !!subbuf_offset(v_read(config, &buf->offset), chan);
	231	}
	232
	233	static inline
4cfec15c MD	234	unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	235	struct lttng_ust_lib_ring_buffer *buf,
1d498196	236	unsigned long idx,
38fae1d3	237	struct lttng_ust_shm_handle *handle)
852c2936	238	{
1d498196	239	return subbuffer_get_data_size(config, &buf->backend, idx, handle);
852c2936 MD	240	}
	241
	242	/*
	243	* Check if all space reservation in a buffer have been committed. This helps
	244	* knowing if an execution context is nested (for per-cpu buffers only).
	245	* This is a very specific ftrace use-case, so we keep this as "internal" API.
	246	*/
	247	static inline
4cfec15c MD	248	int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	249	struct lttng_ust_lib_ring_buffer *buf,
1d498196	250	struct channel *chan,
38fae1d3	251	struct lttng_ust_shm_handle *handle)
852c2936 MD	252	{
852c2936 MD	253	unsigned long offset, idx, commit_count;
730be651	254	struct commit_counters_hot *cc_hot;
852c2936 MD	255
	256	CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
	257	CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
	258
	259	/*
	260	* Read offset and commit count in a loop so they are both read
	261	* atomically wrt interrupts. By deal with interrupt concurrency by
	262	* restarting both reads if the offset has been pushed. Note that given
	263	* we only have to deal with interrupt concurrency here, an interrupt
	264	* modifying the commit count will also modify "offset", so it is safe
	265	* to only check for offset modifications.
	266	*/
	267	do {
	268	offset = v_read(config, &buf->offset);
	269	idx = subbuf_index(offset, chan);
730be651 MD	270	cc_hot = shmp_index(handle, buf->commit_hot, idx);
	271	if (caa_unlikely(!cc_hot))
	272	return 0;
15500a1b	273	commit_count = v_read(config, &cc_hot->cc);
852c2936 MD	274	} while (offset != v_read(config, &buf->offset));
	275
	276	return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
	277	- (commit_count & chan->commit_count_mask) == 0);
	278	}
	279
1b7b0501 MD	280	/*
	281	* Receive end of subbuffer TSC as parameter. It has been read in the
	282	* space reservation loop of either reserve or switch, which ensures it
	283	* progresses monotonically with event records in the buffer. Therefore,
	284	* it ensures that the end timestamp of a subbuffer is <= begin
	285	* timestamp of the following subbuffers.
	286	*/
852c2936	287	static inline
4cfec15c MD	288	void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	289	struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	290	struct channel *chan,
	291	unsigned long offset,
	292	unsigned long commit_count,
1d498196	293	unsigned long idx,
1b7b0501 MD	294	struct lttng_ust_shm_handle *handle,
1b7b0501 MD	295	uint64_t tsc)
852c2936 MD	296	{
	297	unsigned long old_commit_count = commit_count
	298	- chan->backend.subbuf_size;
852c2936 MD	299
852c2936 MD	300	/* Check if all commits have been done */
b5a3dfa5	301	if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
b07cd987 MD	302	- (old_commit_count & chan->commit_count_mask) == 0))
	303	lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
	304	commit_count, idx, handle, tsc);
852c2936 MD	305	}
	306
	307	/*
	308	* lib_ring_buffer_write_commit_counter
	309	*
	310	* For flight recording. must be called after commit.
	311	* This function increments the subbuffer's commit_seq counter each time the
	312	* commit count reaches back the reserve offset (modulo subbuffer size). It is
	313	* useful for crash dump.
	314	*/
	315	static inline
4cfec15c MD	316	void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	317	struct lttng_ust_lib_ring_buffer *buf,
852c2936	318	struct channel *chan,
852c2936 MD	319	unsigned long buf_offset,
852c2936 MD	320	unsigned long commit_count,
d2fe4771 MD	321	struct lttng_ust_shm_handle *handle,
d2fe4771 MD	322	struct commit_counters_hot *cc_hot)
852c2936	323	{
80249235	324	unsigned long commit_seq_old;
852c2936 MD	325
	326	if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
	327	return;
	328
852c2936 MD	329	/*
	330	* subbuf_offset includes commit_count_mask. We can simply
	331	* compare the offsets within the subbuffer without caring about
	332	* buffer full/empty mismatch because offset is never zero here
	333	* (subbuffer header and record headers have non-zero length).
	334	*/
80249235	335	if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
852c2936 MD	336	return;
852c2936 MD	337
d2fe4771	338	commit_seq_old = v_read(config, &cc_hot->seq);
16ec84c8	339	if (caa_likely((long) (commit_seq_old - commit_count) < 0))
d2fe4771	340	v_set(config, &cc_hot->seq, commit_count);
852c2936 MD	341	}
852c2936 MD	342
ddabe860	343	__attribute__((visibility("hidden")))
4cfec15c	344	extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf,
a6352fd4	345	struct channel_backend *chanb, int cpu,
38fae1d3	346	struct lttng_ust_shm_handle *handle,
1d498196	347	struct shm_object *shmobj);
ddabe860 MJ	348
ddabe860 MJ	349	__attribute__((visibility("hidden")))
4cfec15c	350	extern void lib_ring_buffer_free(struct lttng_ust_lib_ring_buffer *buf,
38fae1d3	351	struct lttng_ust_shm_handle *handle);
852c2936 MD	352
852c2936 MD	353	/* Keep track of trap nesting inside ring buffer code */
ddabe860	354	__attribute__((visibility("hidden")))
8c90a710	355	extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting);
852c2936	356
e92f3e28	357	#endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */