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