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

#ifndef _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
#define _LINUX_RING_BUFFER_BACKEND_INTERNAL_H

/*
 * linux/ringbuffer/backend_internal.h
 *
 * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Ring buffer backend (internal helpers).
 *
 * Dual LGPL v2.1/GPL v2 license.
 */

#include <unistd.h>
#include <urcu/compiler.h>

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

/* Ring buffer backend API presented to the frontend */

/* Ring buffer and channel backend create/free */

int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend *bufb,
				   struct channel_backend *chan, int cpu,
				   struct shm_header *shm_header);
void channel_backend_unregister_notifiers(struct channel_backend *chanb);
void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend *bufb);
int channel_backend_init(struct channel_backend *chanb,
			 const char *name,
			 const struct lib_ring_buffer_config *config,
			 void *priv, size_t subbuf_size,
			 size_t num_subbuf, struct shm_header *shm_header);
void channel_backend_free(struct channel_backend *chanb);

void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb);
void channel_backend_reset(struct channel_backend *chanb);

int lib_ring_buffer_backend_init(void);
void lib_ring_buffer_backend_exit(void);

extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend *bufb,
				   size_t offset, const void *src, size_t len,
				   ssize_t pagecpy);

/*
 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
 * exchanged atomically.
 *
 * Top half word, except lowest bit, belongs to "offset", which is used to keep
 * to count the produced buffers.  For overwrite mode, this provides the
 * consumer with the capacity to read subbuffers in order, handling the
 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
 * systems) concurrently with a single execution of get_subbuf (between offset
 * sampling and subbuffer ID exchange).
 */

#define HALF_ULONG_BITS		(CAA_BITS_PER_LONG >> 1)

#define SB_ID_OFFSET_SHIFT	(HALF_ULONG_BITS + 1)
#define SB_ID_OFFSET_COUNT	(1UL << SB_ID_OFFSET_SHIFT)
#define SB_ID_OFFSET_MASK	(~(SB_ID_OFFSET_COUNT - 1))
/*
 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
 */
#define SB_ID_NOREF_SHIFT	(SB_ID_OFFSET_SHIFT - 1)
#define SB_ID_NOREF_COUNT	(1UL << SB_ID_NOREF_SHIFT)
#define SB_ID_NOREF_MASK	SB_ID_NOREF_COUNT
/*
 * In overwrite mode: lowest half of word is used for index.
 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
 * In producer-consumer mode: whole word used for index.
 */
#define SB_ID_INDEX_SHIFT	0
#define SB_ID_INDEX_COUNT	(1UL << SB_ID_INDEX_SHIFT)
#define SB_ID_INDEX_MASK	(SB_ID_NOREF_COUNT - 1)

/*
 * Construct the subbuffer id from offset, index and noref. Use only the index
 * for producer-consumer mode (offset and noref are only used in overwrite
 * mode).
 */
static inline
unsigned long subbuffer_id(const struct lib_ring_buffer_config *config,
			   unsigned long offset, unsigned long noref,
			   unsigned long index)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		return (offset << SB_ID_OFFSET_SHIFT)
		       | (noref << SB_ID_NOREF_SHIFT)
		       | index;
	else
		return index;
}

/*
 * Compare offset with the offset contained within id. Return 1 if the offset
 * bits are identical, else 0.
 */
static inline
int subbuffer_id_compare_offset(const struct lib_ring_buffer_config *config,
				unsigned long id, unsigned long offset)
{
	return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
}

static inline
unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config *config,
				     unsigned long id)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		return id & SB_ID_INDEX_MASK;
	else
		return id;
}

static inline
unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config *config,
				    unsigned long id)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		return !!(id & SB_ID_NOREF_MASK);
	else
		return 1;
}

/*
 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
 * needed.
 */
static inline
void subbuffer_id_set_noref(const struct lib_ring_buffer_config *config,
			    unsigned long *id)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		*id |= SB_ID_NOREF_MASK;
}

static inline
void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config,
				   unsigned long *id, unsigned long offset)
{
	unsigned long tmp;

	if (config->mode == RING_BUFFER_OVERWRITE) {
		tmp = *id;
		tmp &= ~SB_ID_OFFSET_MASK;
		tmp |= offset << SB_ID_OFFSET_SHIFT;
		tmp |= SB_ID_NOREF_MASK;
		/* Volatile store, read concurrently by readers. */
		CMM_ACCESS_ONCE(*id) = tmp;
	}
}

/* No volatile access, since already used locally */
static inline
void subbuffer_id_clear_noref(const struct lib_ring_buffer_config *config,
			      unsigned long *id)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		*id &= ~SB_ID_NOREF_MASK;
}

/*
 * For overwrite mode, cap the number of subbuffers per buffer to:
 * 2^16 on 32-bit architectures
 * 2^32 on 64-bit architectures
 * This is required to fit in the index part of the ID. Return 0 on success,
 * -EPERM on failure.
 */
static inline
int subbuffer_id_check_index(const struct lib_ring_buffer_config *config,
			     unsigned long num_subbuf)
{
	if (config->mode == RING_BUFFER_OVERWRITE)
		return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
	else
		return 0;
}

static inline
void subbuffer_count_record(const struct lib_ring_buffer_config *config,
			    struct lib_ring_buffer_backend *bufb,
			    unsigned long idx)
{
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
	v_inc(config, &shmp(bufb->array)[sb_bindex]->records_commit);
}

/*
 * Reader has exclusive subbuffer access for record consumption. No need to
 * perform the decrement atomically.
 */
static inline
void subbuffer_consume_record(const struct lib_ring_buffer_config *config,
			      struct lib_ring_buffer_backend *bufb)
{
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
	CHAN_WARN_ON(bufb->chan,
		     !v_read(config, &shmp(bufb->array)[sb_bindex]->records_unread));
	/* Non-atomic decrement protected by exclusive subbuffer access */
	_v_dec(config, &shmp(bufb->array)[sb_bindex]->records_unread);
	v_inc(config, &bufb->records_read);
}

static inline
unsigned long subbuffer_get_records_count(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer_backend *bufb,
				unsigned long idx)
{
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
	return v_read(config, &shmp(bufb->array)[sb_bindex]->records_commit);
}

/*
 * Must be executed at subbuffer delivery when the writer has _exclusive_
 * subbuffer access. See ring_buffer_check_deliver() for details.
 * ring_buffer_get_records_count() must be called to get the records count
 * before this function, because it resets the records_commit count.
 */
static inline
unsigned long subbuffer_count_records_overrun(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer_backend *bufb,
				unsigned long idx)
{
	struct lib_ring_buffer_backend_pages *pages;
	unsigned long overruns, sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
	pages = shmp(bufb->array)[sb_bindex];
	overruns = v_read(config, &pages->records_unread);
	v_set(config, &pages->records_unread,
	      v_read(config, &pages->records_commit));
	v_set(config, &pages->records_commit, 0);

	return overruns;
}

static inline
void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
			     struct lib_ring_buffer_backend *bufb,
			     unsigned long idx,
			     unsigned long data_size)
{
	struct lib_ring_buffer_backend_pages *pages;
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
	pages = shmp(bufb->array)[sb_bindex];
	pages->data_size = data_size;
}

static inline
unsigned long subbuffer_get_read_data_size(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer_backend *bufb)
{
	struct lib_ring_buffer_backend_pages *pages;
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
	pages = shmp(bufb->array)[sb_bindex];
	return pages->data_size;
}

static inline
unsigned long subbuffer_get_data_size(
				const struct lib_ring_buffer_config *config,
				struct lib_ring_buffer_backend *bufb,
				unsigned long idx)
{
	struct lib_ring_buffer_backend_pages *pages;
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
	pages = shmp(bufb->array)[sb_bindex];
	return pages->data_size;
}

/**
 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
 *                               writer.
 */
static inline
void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
				 struct lib_ring_buffer_backend *bufb,
				 unsigned long idx)
{
	unsigned long id, new_id;

	if (config->mode != RING_BUFFER_OVERWRITE)
		return;

	/*
	 * Performing a volatile access to read the sb_pages, because we want to
	 * read a coherent version of the pointer and the associated noref flag.
	 */
	id = CMM_ACCESS_ONCE(shmp(bufb->buf_wsb)[idx].id);
	for (;;) {
		/* This check is called on the fast path for each record. */
		if (likely(!subbuffer_id_is_noref(config, id))) {
			/*
			 * Store after load dependency ordering the writes to
			 * the subbuffer after load and test of the noref flag
			 * matches the memory barrier implied by the cmpxchg()
			 * in update_read_sb_index().
			 */
			return;	/* Already writing to this buffer */
		}
		new_id = id;
		subbuffer_id_clear_noref(config, &new_id);
		new_id = uatomic_cmpxchg(&shmp(bufb->buf_wsb)[idx].id, id, new_id);
		if (likely(new_id == id))
			break;
		id = new_id;
	}
}

/**
 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
 *                                    called by writer.
 */
static inline
void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *config,
				      struct lib_ring_buffer_backend *bufb,
				      unsigned long idx, unsigned long offset)
{
	if (config->mode != RING_BUFFER_OVERWRITE)
		return;

	/*
	 * Because ring_buffer_set_noref() is only called by a single thread
	 * (the one which updated the cc_sb value), there are no concurrent
	 * updates to take care of: other writers have not updated cc_sb, so
	 * they cannot set the noref flag, and concurrent readers cannot modify
	 * the pointer because the noref flag is not set yet.
	 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
	 * to the subbuffer before this set noref operation.
	 * subbuffer_set_noref() uses a volatile store to deal with concurrent
	 * readers of the noref flag.
	 */
	CHAN_WARN_ON(bufb->chan,
		     subbuffer_id_is_noref(config, shmp(bufb->buf_wsb)[idx].id));
	/*
	 * Memory barrier that ensures counter stores are ordered before set
	 * noref and offset.
	 */
	cmm_smp_mb();
	subbuffer_id_set_noref_offset(config, &shmp(bufb->buf_wsb)[idx].id, offset);
}

/**
 * update_read_sb_index - Read-side subbuffer index update.
 */
static inline
int update_read_sb_index(const struct lib_ring_buffer_config *config,
			 struct lib_ring_buffer_backend *bufb,
			 struct channel_backend *chanb,
			 unsigned long consumed_idx,
			 unsigned long consumed_count)
{
	unsigned long old_id, new_id;

	if (config->mode == RING_BUFFER_OVERWRITE) {
		/*
		 * Exchange the target writer subbuffer with our own unused
		 * subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
		 * old_wpage, because the value read will be confirmed by the
		 * following cmpxchg().
		 */
		old_id = shmp(bufb->buf_wsb)[consumed_idx].id;
		if (unlikely(!subbuffer_id_is_noref(config, old_id)))
			return -EAGAIN;
		/*
		 * Make sure the offset count we are expecting matches the one
		 * indicated by the writer.
		 */
		if (unlikely(!subbuffer_id_compare_offset(config, old_id,
							  consumed_count)))
			return -EAGAIN;
		CHAN_WARN_ON(bufb->chan,
			     !subbuffer_id_is_noref(config, bufb->buf_rsb.id));
		subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
					      consumed_count);
		new_id = uatomic_cmpxchg(&shmp(bufb->buf_wsb)[consumed_idx].id, old_id,
				 bufb->buf_rsb.id);
		if (unlikely(old_id != new_id))
			return -EAGAIN;
		bufb->buf_rsb.id = new_id;
	} else {
		/* No page exchange, use the writer page directly */
		bufb->buf_rsb.id = shmp(bufb->buf_wsb)[consumed_idx].id;
	}
	return 0;
}

/*
 * Use the architecture-specific memcpy implementation for constant-sized
 * inputs, but rely on an inline memcpy for length statically unknown.
 * The function call to memcpy is just way too expensive for a fast path.
 */
#define lib_ring_buffer_do_copy(config, dest, src, len)		\
do {								\
	size_t __len = (len);					\
	if (__builtin_constant_p(len))				\
		memcpy(dest, src, __len);			\
	else							\
		inline_memcpy(dest, src, __len);		\
} while (0)

#endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */
Commit	Line	Data
852c2936 MD	1	#ifndef _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
	2	#define _LINUX_RING_BUFFER_BACKEND_INTERNAL_H
	3
	4	/*
	5	* linux/ringbuffer/backend_internal.h
	6	*
	7	* Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	8	*
	9	* Ring buffer backend (internal helpers).
	10	*
	11	* Dual LGPL v2.1/GPL v2 license.
	12	*/
	13
14641deb MD	14	#include <unistd.h>
	15	#include <urcu/compiler.h>
	16
8d8a24c8	17	#include <ust/ringbuffer-config.h>
4931a13e MD	18	#include "backend_types.h"
4931a13e MD	19	#include "frontend_types.h"
a6352fd4	20	#include "shm.h"
852c2936 MD	21
	22	/* Ring buffer backend API presented to the frontend */
	23
	24	/* Ring buffer and channel backend create/free */
	25
	26	int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend *bufb,
a6352fd4 MD	27	struct channel_backend *chan, int cpu,
a6352fd4 MD	28	struct shm_header *shm_header);
852c2936 MD	29	void channel_backend_unregister_notifiers(struct channel_backend *chanb);
	30	void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend *bufb);
	31	int channel_backend_init(struct channel_backend *chanb,
	32	const char *name,
	33	const struct lib_ring_buffer_config *config,
	34	void *priv, size_t subbuf_size,
a6352fd4	35	size_t num_subbuf, struct shm_header *shm_header);
852c2936 MD	36	void channel_backend_free(struct channel_backend *chanb);
	37
	38	void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend *bufb);
	39	void channel_backend_reset(struct channel_backend *chanb);
	40
	41	int lib_ring_buffer_backend_init(void);
	42	void lib_ring_buffer_backend_exit(void);
	43
	44	extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend *bufb,
	45	size_t offset, const void *src, size_t len,
	46	ssize_t pagecpy);
	47
	48	/*
	49	* Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
	50	* exchanged atomically.
	51	*
	52	* Top half word, except lowest bit, belongs to "offset", which is used to keep
	53	* to count the produced buffers. For overwrite mode, this provides the
	54	* consumer with the capacity to read subbuffers in order, handling the
	55	* situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
	56	* systems) concurrently with a single execution of get_subbuf (between offset
	57	* sampling and subbuffer ID exchange).
	58	*/
	59
14641deb	60	#define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
852c2936 MD	61
	62	#define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
	63	#define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
	64	#define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
	65	/*
	66	* Lowest bit of top word half belongs to noref. Used only for overwrite mode.
	67	*/
	68	#define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
	69	#define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
	70	#define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
	71	/*
	72	* In overwrite mode: lowest half of word is used for index.
	73	* Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
	74	* In producer-consumer mode: whole word used for index.
	75	*/
	76	#define SB_ID_INDEX_SHIFT 0
	77	#define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
	78	#define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
	79
	80	/*
	81	* Construct the subbuffer id from offset, index and noref. Use only the index
	82	* for producer-consumer mode (offset and noref are only used in overwrite
	83	* mode).
	84	*/
	85	static inline
	86	unsigned long subbuffer_id(const struct lib_ring_buffer_config *config,
	87	unsigned long offset, unsigned long noref,
	88	unsigned long index)
	89	{
	90	if (config->mode == RING_BUFFER_OVERWRITE)
	91	return (offset << SB_ID_OFFSET_SHIFT)
	92	\| (noref << SB_ID_NOREF_SHIFT)
	93	\| index;
	94	else
	95	return index;
	96	}
	97
	98	/*
	99	* Compare offset with the offset contained within id. Return 1 if the offset
	100	* bits are identical, else 0.
	101	*/
	102	static inline
	103	int subbuffer_id_compare_offset(const struct lib_ring_buffer_config *config,
	104	unsigned long id, unsigned long offset)
	105	{
	106	return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
	107	}
	108
	109	static inline
	110	unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config *config,
	111	unsigned long id)
	112	{
	113	if (config->mode == RING_BUFFER_OVERWRITE)
	114	return id & SB_ID_INDEX_MASK;
	115	else
	116	return id;
	117	}
	118
	119	static inline
	120	unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config *config,
	121	unsigned long id)
	122	{
	123	if (config->mode == RING_BUFFER_OVERWRITE)
	124	return !!(id & SB_ID_NOREF_MASK);
125	else
126	return 1;
127	}
128
129	/*
130	* Only used by reader on subbuffer ID it has exclusive access to. No volatile
131	* needed.
132	*/
133	static inline
134	void subbuffer_id_set_noref(const struct lib_ring_buffer_config *config,
135	unsigned long *id)
136	{
137	if (config->mode == RING_BUFFER_OVERWRITE)
138	*id \|= SB_ID_NOREF_MASK;
139	}
140
141	static inline
142	void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config *config,
143	unsigned long *id, unsigned long offset)
144	{
145	unsigned long tmp;
146
147	if (config->mode == RING_BUFFER_OVERWRITE) {
148	tmp = *id;
149	tmp &= ~SB_ID_OFFSET_MASK;
150	tmp \|= offset << SB_ID_OFFSET_SHIFT;
151	tmp \|= SB_ID_NOREF_MASK;
152	/* Volatile store, read concurrently by readers. */
14641deb	153	CMM_ACCESS_ONCE(*id) = tmp;
852c2936 MD	154	}
	155	}
	156
	157	/* No volatile access, since already used locally */
	158	static inline
	159	void subbuffer_id_clear_noref(const struct lib_ring_buffer_config *config,
	160	unsigned long *id)
	161	{
	162	if (config->mode == RING_BUFFER_OVERWRITE)
	163	*id &= ~SB_ID_NOREF_MASK;
	164	}
	165
	166	/*
	167	* For overwrite mode, cap the number of subbuffers per buffer to:
	168	* 2^16 on 32-bit architectures
	169	* 2^32 on 64-bit architectures
	170	* This is required to fit in the index part of the ID. Return 0 on success,
	171	* -EPERM on failure.
	172	*/
	173	static inline
	174	int subbuffer_id_check_index(const struct lib_ring_buffer_config *config,
	175	unsigned long num_subbuf)
	176	{
	177	if (config->mode == RING_BUFFER_OVERWRITE)
	178	return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
	179	else
	180	return 0;
	181	}
	182
	183	static inline
	184	void subbuffer_count_record(const struct lib_ring_buffer_config *config,
	185	struct lib_ring_buffer_backend *bufb,
	186	unsigned long idx)
	187	{
	188	unsigned long sb_bindex;
	189
a6352fd4 MD	190	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
a6352fd4 MD	191	v_inc(config, &shmp(bufb->array)[sb_bindex]->records_commit);
852c2936 MD	192	}
	193
	194	/*
	195	* Reader has exclusive subbuffer access for record consumption. No need to
	196	* perform the decrement atomically.
	197	*/
	198	static inline
	199	void subbuffer_consume_record(const struct lib_ring_buffer_config *config,
	200	struct lib_ring_buffer_backend *bufb)
	201	{
	202	unsigned long sb_bindex;
	203
	204	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
	205	CHAN_WARN_ON(bufb->chan,
a6352fd4	206	!v_read(config, &shmp(bufb->array)[sb_bindex]->records_unread));
852c2936	207	/* Non-atomic decrement protected by exclusive subbuffer access */
a6352fd4	208	_v_dec(config, &shmp(bufb->array)[sb_bindex]->records_unread);
852c2936 MD	209	v_inc(config, &bufb->records_read);
	210	}
	211
	212	static inline
	213	unsigned long subbuffer_get_records_count(
	214	const struct lib_ring_buffer_config *config,
	215	struct lib_ring_buffer_backend *bufb,
	216	unsigned long idx)
	217	{
	218	unsigned long sb_bindex;
	219
a6352fd4 MD	220	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
a6352fd4 MD	221	return v_read(config, &shmp(bufb->array)[sb_bindex]->records_commit);
852c2936 MD	222	}
	223
	224	/*
	225	* Must be executed at subbuffer delivery when the writer has _exclusive_
	226	* subbuffer access. See ring_buffer_check_deliver() for details.
	227	* ring_buffer_get_records_count() must be called to get the records count
	228	* before this function, because it resets the records_commit count.
	229	*/
	230	static inline
	231	unsigned long subbuffer_count_records_overrun(
	232	const struct lib_ring_buffer_config *config,
	233	struct lib_ring_buffer_backend *bufb,
	234	unsigned long idx)
	235	{
	236	struct lib_ring_buffer_backend_pages *pages;
	237	unsigned long overruns, sb_bindex;
	238
a6352fd4 MD	239	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
a6352fd4 MD	240	pages = shmp(bufb->array)[sb_bindex];
852c2936 MD	241	overruns = v_read(config, &pages->records_unread);
	242	v_set(config, &pages->records_unread,
	243	v_read(config, &pages->records_commit));
	244	v_set(config, &pages->records_commit, 0);
	245
	246	return overruns;
	247	}
	248
	249	static inline
	250	void subbuffer_set_data_size(const struct lib_ring_buffer_config *config,
	251	struct lib_ring_buffer_backend *bufb,
	252	unsigned long idx,
	253	unsigned long data_size)
	254	{
	255	struct lib_ring_buffer_backend_pages *pages;
	256	unsigned long sb_bindex;
	257
a6352fd4 MD	258	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
a6352fd4 MD	259	pages = shmp(bufb->array)[sb_bindex];
852c2936 MD	260	pages->data_size = data_size;
	261	}
	262
	263	static inline
	264	unsigned long subbuffer_get_read_data_size(
	265	const struct lib_ring_buffer_config *config,
	266	struct lib_ring_buffer_backend *bufb)
	267	{
	268	struct lib_ring_buffer_backend_pages *pages;
	269	unsigned long sb_bindex;
	270
	271	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
a6352fd4	272	pages = shmp(bufb->array)[sb_bindex];
852c2936 MD	273	return pages->data_size;
	274	}
	275
	276	static inline
	277	unsigned long subbuffer_get_data_size(
	278	const struct lib_ring_buffer_config *config,
	279	struct lib_ring_buffer_backend *bufb,
	280	unsigned long idx)
	281	{
	282	struct lib_ring_buffer_backend_pages *pages;
	283	unsigned long sb_bindex;
	284
a6352fd4 MD	285	sb_bindex = subbuffer_id_get_index(config, shmp(bufb->buf_wsb)[idx].id);
a6352fd4 MD	286	pages = shmp(bufb->array)[sb_bindex];
852c2936 MD	287	return pages->data_size;
	288	}
	289
	290	/**
	291	* lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
	292	* writer.
	293	*/
	294	static inline
	295	void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config *config,
	296	struct lib_ring_buffer_backend *bufb,
	297	unsigned long idx)
	298	{
	299	unsigned long id, new_id;
	300
	301	if (config->mode != RING_BUFFER_OVERWRITE)
	302	return;
	303
	304	/*
	305	* Performing a volatile access to read the sb_pages, because we want to
	306	* read a coherent version of the pointer and the associated noref flag.
	307	*/
a6352fd4	308	id = CMM_ACCESS_ONCE(shmp(bufb->buf_wsb)[idx].id);
852c2936 MD	309	for (;;) {
	310	/* This check is called on the fast path for each record. */
	311	if (likely(!subbuffer_id_is_noref(config, id))) {
	312	/*
	313	* Store after load dependency ordering the writes to
	314	* the subbuffer after load and test of the noref flag
	315	* matches the memory barrier implied by the cmpxchg()
	316	* in update_read_sb_index().
	317	*/
	318	return; /* Already writing to this buffer */
	319	}
	320	new_id = id;
	321	subbuffer_id_clear_noref(config, &new_id);
a6352fd4	322	new_id = uatomic_cmpxchg(&shmp(bufb->buf_wsb)[idx].id, id, new_id);
852c2936 MD	323	if (likely(new_id == id))
	324	break;
	325	id = new_id;
	326	}
	327	}
	328
	329	/**
	330	* lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
	331	* called by writer.
	332	*/
	333	static inline
	334	void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config *config,
	335	struct lib_ring_buffer_backend *bufb,
	336	unsigned long idx, unsigned long offset)
	337	{
	338	if (config->mode != RING_BUFFER_OVERWRITE)
	339	return;
	340
	341	/*
	342	* Because ring_buffer_set_noref() is only called by a single thread
	343	* (the one which updated the cc_sb value), there are no concurrent
	344	* updates to take care of: other writers have not updated cc_sb, so
	345	* they cannot set the noref flag, and concurrent readers cannot modify
	346	* the pointer because the noref flag is not set yet.
	347	* The smp_wmb() in ring_buffer_commit() takes care of ordering writes
	348	* to the subbuffer before this set noref operation.
	349	* subbuffer_set_noref() uses a volatile store to deal with concurrent
	350	* readers of the noref flag.
	351	*/
	352	CHAN_WARN_ON(bufb->chan,
a6352fd4	353	subbuffer_id_is_noref(config, shmp(bufb->buf_wsb)[idx].id));
852c2936 MD	354	/*
	355	* Memory barrier that ensures counter stores are ordered before set
	356	* noref and offset.
	357	*/
14641deb	358	cmm_smp_mb();
a6352fd4	359	subbuffer_id_set_noref_offset(config, &shmp(bufb->buf_wsb)[idx].id, offset);
852c2936 MD	360	}
	361
	362	/**
	363	* update_read_sb_index - Read-side subbuffer index update.
	364	*/
	365	static inline
	366	int update_read_sb_index(const struct lib_ring_buffer_config *config,
	367	struct lib_ring_buffer_backend *bufb,
	368	struct channel_backend *chanb,
	369	unsigned long consumed_idx,
	370	unsigned long consumed_count)
	371	{
	372	unsigned long old_id, new_id;
	373
	374	if (config->mode == RING_BUFFER_OVERWRITE) {
	375	/*
	376	* Exchange the target writer subbuffer with our own unused
14641deb	377	* subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
852c2936 MD	378	* old_wpage, because the value read will be confirmed by the
	379	* following cmpxchg().
	380	*/
a6352fd4	381	old_id = shmp(bufb->buf_wsb)[consumed_idx].id;
852c2936 MD	382	if (unlikely(!subbuffer_id_is_noref(config, old_id)))
	383	return -EAGAIN;
	384	/*
	385	* Make sure the offset count we are expecting matches the one
	386	* indicated by the writer.
	387	*/
	388	if (unlikely(!subbuffer_id_compare_offset(config, old_id,
	389	consumed_count)))
	390	return -EAGAIN;
	391	CHAN_WARN_ON(bufb->chan,
	392	!subbuffer_id_is_noref(config, bufb->buf_rsb.id));
	393	subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
	394	consumed_count);
a6352fd4	395	new_id = uatomic_cmpxchg(&shmp(bufb->buf_wsb)[consumed_idx].id, old_id,
852c2936 MD	396	bufb->buf_rsb.id);
	397	if (unlikely(old_id != new_id))
	398	return -EAGAIN;
	399	bufb->buf_rsb.id = new_id;
	400	} else {
	401	/* No page exchange, use the writer page directly */
a6352fd4	402	bufb->buf_rsb.id = shmp(bufb->buf_wsb)[consumed_idx].id;
852c2936 MD	403	}
	404	return 0;
	405	}
	406
	407	/*
	408	* Use the architecture-specific memcpy implementation for constant-sized
	409	* inputs, but rely on an inline memcpy for length statically unknown.
	410	* The function call to memcpy is just way too expensive for a fast path.
	411	*/
	412	#define lib_ring_buffer_do_copy(config, dest, src, len) \
	413	do { \
	414	size_t __len = (len); \
	415	if (__builtin_constant_p(len)) \
	416	memcpy(dest, src, __len); \
	417	else \
	418	inline_memcpy(dest, src, __len); \
	419	} while (0)
	420
	421	#endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */