[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"
#include "ust-helper.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

LTTNG_HIDDEN
extern
int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
		void *client_ctx);

LTTNG_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);

LTTNG_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);
}

LTTNG_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);
LTTNG_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 */
LTTNG_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"
071dec43	24	#include "ust-helper.h"
852c2936 MD	25
	26	/* Buffer offset macros */
	27
	28	/* buf_trunc mask selects only the buffer number. */
	29	static inline
	30	unsigned long buf_trunc(unsigned long offset, struct channel *chan)
	31	{
	32	return offset & ~(chan->backend.buf_size - 1);
	33
	34	}
	35
	36	/* Select the buffer number value (counter). */
	37	static inline
	38	unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
	39	{
	40	return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
	41	}
	42
	43	/* buf_offset mask selects only the offset within the current buffer. */
	44	static inline
	45	unsigned long buf_offset(unsigned long offset, struct channel *chan)
	46	{
	47	return offset & (chan->backend.buf_size - 1);
	48	}
	49
	50	/* subbuf_offset mask selects the offset within the current subbuffer. */
	51	static inline
	52	unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
	53	{
	54	return offset & (chan->backend.subbuf_size - 1);
	55	}
	56
	57	/* subbuf_trunc mask selects the subbuffer number. */
	58	static inline
	59	unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
	60	{
	61	return offset & ~(chan->backend.subbuf_size - 1);
	62	}
	63
	64	/* subbuf_align aligns the offset to the next subbuffer. */
	65	static inline
	66	unsigned long subbuf_align(unsigned long offset, struct channel *chan)
	67	{
	68	return (offset + chan->backend.subbuf_size)
	69	& ~(chan->backend.subbuf_size - 1);
	70	}
	71
	72	/* subbuf_index returns the index of the current subbuffer within the buffer. */
	73	static inline
	74	unsigned long subbuf_index(unsigned long offset, struct channel *chan)
	75	{
	76	return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
	77	}
	78
	79	/*
	80	* Last TSC comparison functions. Check if the current TSC overflows tsc_bits
	81	* bits from the last TSC read. When overflows are detected, the full 64-bit
	82	* timestamp counter should be written in the record header. Reads and writes
	83	* last_tsc atomically.
	84	*/
	85
14641deb	86	#if (CAA_BITS_PER_LONG == 32)
852c2936	87	static inline
4cfec15c	88	void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	89	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	90	{
	91	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	92	return;
	93
	94	/*
	95	* Ensure the compiler performs this update in a single instruction.
	96	*/
	97	v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
	98	}
	99
	100	static inline
4cfec15c	101	int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	102	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	103	{
	104	unsigned long tsc_shifted;
	105
	106	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	107	return 0;
	108
	109	tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
b5a3dfa5	110	if (caa_unlikely(tsc_shifted
852c2936 MD	111	- (unsigned long)v_read(config, &buf->last_tsc)))
	112	return 1;
	113	else
	114	return 0;
	115	}
	116	#else
	117	static inline
4cfec15c	118	void save_last_tsc(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	119	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	120	{
	121	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	122	return;
	123
	124	v_set(config, &buf->last_tsc, (unsigned long)tsc);
	125	}
	126
	127	static inline
4cfec15c	128	int last_tsc_overflow(const struct lttng_ust_lib_ring_buffer_config *config,
2fed87ae	129	struct lttng_ust_lib_ring_buffer *buf, uint64_t tsc)
852c2936 MD	130	{
	131	if (config->tsc_bits == 0 \|\| config->tsc_bits == 64)
	132	return 0;
	133
b5a3dfa5	134	if (caa_unlikely((tsc - v_read(config, &buf->last_tsc))
852c2936 MD	135	>> config->tsc_bits))
	136	return 1;
	137	else
	138	return 0;
	139	}
	140	#endif
	141
071dec43	142	LTTNG_HIDDEN
852c2936	143	extern
e56bb47c MD	144	int lib_ring_buffer_reserve_slow(struct lttng_ust_lib_ring_buffer_ctx *ctx,
e56bb47c MD	145	void *client_ctx);
852c2936	146
071dec43	147	LTTNG_HIDDEN
852c2936	148	extern
4cfec15c	149	void lib_ring_buffer_switch_slow(struct lttng_ust_lib_ring_buffer *buf,
1d498196	150	enum switch_mode mode,
38fae1d3	151	struct lttng_ust_shm_handle *handle);
852c2936	152
071dec43	153	LTTNG_HIDDEN
b07cd987 MD	154	void lib_ring_buffer_check_deliver_slow(const struct lttng_ust_lib_ring_buffer_config *config,
	155	struct lttng_ust_lib_ring_buffer *buf,
	156	struct channel *chan,
	157	unsigned long offset,
	158	unsigned long commit_count,
	159	unsigned long idx,
	160	struct lttng_ust_shm_handle *handle,
	161	uint64_t tsc);
	162
852c2936 MD	163	/* Buffer write helpers */
	164
	165	static inline
4cfec15c	166	void lib_ring_buffer_reserve_push_reader(struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	167	struct channel *chan,
	168	unsigned long offset)
	169	{
	170	unsigned long consumed_old, consumed_new;
	171
	172	do {
14641deb	173	consumed_old = uatomic_read(&buf->consumed);
852c2936 MD	174	/*
	175	* If buffer is in overwrite mode, push the reader consumed
	176	* count if the write position has reached it and we are not
	177	* at the first iteration (don't push the reader farther than
	178	* the writer). This operation can be done concurrently by many
	179	* writers in the same buffer, the writer being at the farthest
	180	* write position sub-buffer index in the buffer being the one
	181	* which will win this loop.
	182	*/
b5a3dfa5	183	if (caa_unlikely(subbuf_trunc(offset, chan)
852c2936 MD	184	- subbuf_trunc(consumed_old, chan)
	185	>= chan->backend.buf_size))
	186	consumed_new = subbuf_align(consumed_old, chan);
	187	else
	188	return;
b5a3dfa5	189	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
852c2936 MD	190	consumed_new) != consumed_old));
	191	}
	192
4c742ffd MD	193	/*
	194	* Move consumed position to the beginning of subbuffer in which the
	195	* write offset is. Should only be used on ring buffers that are not
	196	* actively being written into, because clear_reader does not take into
	197	* account the commit counters when moving the consumed position, which
	198	* can make concurrent trace producers or consumers observe consumed
	199	* position further than the write offset, which breaks ring buffer
	200	* algorithm guarantees.
	201	*/
beca55a1 MD	202	static inline
	203	void lib_ring_buffer_clear_reader(struct lttng_ust_lib_ring_buffer *buf,
	204	struct lttng_ust_shm_handle *handle)
	205	{
	206	struct channel *chan;
	207	const struct lttng_ust_lib_ring_buffer_config *config;
	208	unsigned long offset, consumed_old, consumed_new;
	209
	210	chan = shmp(handle, buf->backend.chan);
	211	if (!chan)
	212	return;
	213	config = &chan->backend.config;
	214
	215	do {
	216	offset = v_read(config, &buf->offset);
	217	consumed_old = uatomic_read(&buf->consumed);
4c742ffd MD	218	CHAN_WARN_ON(chan, (long) (subbuf_trunc(offset, chan)
	219	- subbuf_trunc(consumed_old, chan))
	220	< 0);
	221	consumed_new = subbuf_trunc(offset, chan);
beca55a1 MD	222	} while (caa_unlikely(uatomic_cmpxchg(&buf->consumed, consumed_old,
	223	consumed_new) != consumed_old));
	224	}
	225
852c2936	226	static inline
4cfec15c MD	227	int lib_ring_buffer_pending_data(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	228	struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	229	struct channel *chan)
	230	{
	231	return !!subbuf_offset(v_read(config, &buf->offset), chan);
	232	}
	233
	234	static inline
4cfec15c MD	235	unsigned long lib_ring_buffer_get_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	236	struct lttng_ust_lib_ring_buffer *buf,
1d498196	237	unsigned long idx,
38fae1d3	238	struct lttng_ust_shm_handle *handle)
852c2936	239	{
1d498196	240	return subbuffer_get_data_size(config, &buf->backend, idx, handle);
852c2936 MD	241	}
	242
	243	/*
	244	* Check if all space reservation in a buffer have been committed. This helps
	245	* knowing if an execution context is nested (for per-cpu buffers only).
	246	* This is a very specific ftrace use-case, so we keep this as "internal" API.
	247	*/
	248	static inline
4cfec15c MD	249	int lib_ring_buffer_reserve_committed(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	250	struct lttng_ust_lib_ring_buffer *buf,
1d498196	251	struct channel *chan,
38fae1d3	252	struct lttng_ust_shm_handle *handle)
852c2936 MD	253	{
852c2936 MD	254	unsigned long offset, idx, commit_count;
730be651	255	struct commit_counters_hot *cc_hot;
852c2936 MD	256
	257	CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
	258	CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
	259
	260	/*
	261	* Read offset and commit count in a loop so they are both read
	262	* atomically wrt interrupts. By deal with interrupt concurrency by
	263	* restarting both reads if the offset has been pushed. Note that given
	264	* we only have to deal with interrupt concurrency here, an interrupt
	265	* modifying the commit count will also modify "offset", so it is safe
	266	* to only check for offset modifications.
	267	*/
	268	do {
	269	offset = v_read(config, &buf->offset);
	270	idx = subbuf_index(offset, chan);
730be651 MD	271	cc_hot = shmp_index(handle, buf->commit_hot, idx);
	272	if (caa_unlikely(!cc_hot))
	273	return 0;
15500a1b	274	commit_count = v_read(config, &cc_hot->cc);
852c2936 MD	275	} while (offset != v_read(config, &buf->offset));
	276
	277	return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
	278	- (commit_count & chan->commit_count_mask) == 0);
	279	}
	280
1b7b0501 MD	281	/*
	282	* Receive end of subbuffer TSC as parameter. It has been read in the
	283	* space reservation loop of either reserve or switch, which ensures it
	284	* progresses monotonically with event records in the buffer. Therefore,
	285	* it ensures that the end timestamp of a subbuffer is <= begin
	286	* timestamp of the following subbuffers.
	287	*/
852c2936	288	static inline
4cfec15c MD	289	void lib_ring_buffer_check_deliver(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	290	struct lttng_ust_lib_ring_buffer *buf,
852c2936 MD	291	struct channel *chan,
	292	unsigned long offset,
	293	unsigned long commit_count,
1d498196	294	unsigned long idx,
1b7b0501 MD	295	struct lttng_ust_shm_handle *handle,
1b7b0501 MD	296	uint64_t tsc)
852c2936 MD	297	{
	298	unsigned long old_commit_count = commit_count
	299	- chan->backend.subbuf_size;
852c2936 MD	300
852c2936 MD	301	/* Check if all commits have been done */
b5a3dfa5	302	if (caa_unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
b07cd987 MD	303	- (old_commit_count & chan->commit_count_mask) == 0))
	304	lib_ring_buffer_check_deliver_slow(config, buf, chan, offset,
	305	commit_count, idx, handle, tsc);
852c2936 MD	306	}
	307
	308	/*
	309	* lib_ring_buffer_write_commit_counter
	310	*
	311	* For flight recording. must be called after commit.
	312	* This function increments the subbuffer's commit_seq counter each time the
	313	* commit count reaches back the reserve offset (modulo subbuffer size). It is
	314	* useful for crash dump.
	315	*/
	316	static inline
4cfec15c MD	317	void lib_ring_buffer_write_commit_counter(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	318	struct lttng_ust_lib_ring_buffer *buf,
852c2936	319	struct channel *chan,
852c2936 MD	320	unsigned long buf_offset,
852c2936 MD	321	unsigned long commit_count,
d2fe4771 MD	322	struct lttng_ust_shm_handle *handle,
d2fe4771 MD	323	struct commit_counters_hot *cc_hot)
852c2936	324	{
80249235	325	unsigned long commit_seq_old;
852c2936 MD	326
	327	if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
	328	return;
	329
852c2936 MD	330	/*
	331	* subbuf_offset includes commit_count_mask. We can simply
	332	* compare the offsets within the subbuffer without caring about
	333	* buffer full/empty mismatch because offset is never zero here
	334	* (subbuffer header and record headers have non-zero length).
	335	*/
80249235	336	if (caa_unlikely(subbuf_offset(buf_offset - commit_count, chan)))
852c2936 MD	337	return;
852c2936 MD	338
d2fe4771	339	commit_seq_old = v_read(config, &cc_hot->seq);
16ec84c8	340	if (caa_likely((long) (commit_seq_old - commit_count) < 0))
d2fe4771	341	v_set(config, &cc_hot->seq, commit_count);
852c2936 MD	342	}
852c2936 MD	343
071dec43	344	LTTNG_HIDDEN
4cfec15c	345	extern int lib_ring_buffer_create(struct lttng_ust_lib_ring_buffer *buf,
a6352fd4	346	struct channel_backend *chanb, int cpu,
38fae1d3	347	struct lttng_ust_shm_handle *handle,
1d498196	348	struct shm_object *shmobj);
071dec43	349	LTTNG_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 */
071dec43	354	LTTNG_HIDDEN
8c90a710	355	extern DECLARE_URCU_TLS(unsigned int, lib_ring_buffer_nesting);
852c2936	356
e92f3e28	357	#endif /* _LTTNG_RING_BUFFER_FRONTEND_INTERNAL_H */