[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 <lttng/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 lttng_ust_lib_ring_buffer_backend *bufb,
				   struct channel_backend *chan, int cpu,
				   struct lttng_ust_shm_handle *handle,
				   struct shm_object *shmobj);
void channel_backend_unregister_notifiers(struct channel_backend *chanb);
void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend *bufb);
int channel_backend_init(struct channel_backend *chanb,
			 const char *name,
			 const struct lttng_ust_lib_ring_buffer_config *config,
			 size_t subbuf_size,
			 size_t num_subbuf, struct lttng_ust_shm_handle *handle);
void channel_backend_free(struct channel_backend *chanb,
			  struct lttng_ust_shm_handle *handle);

void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb,
				   struct lttng_ust_shm_handle *handle);
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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_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 lttng_ust_lib_ring_buffer_config *config,
			    struct lttng_ust_lib_ring_buffer_backend *bufb,
			    unsigned long idx, struct lttng_ust_shm_handle *handle)
{
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
	v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->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 lttng_ust_lib_ring_buffer_config *config,
			      struct lttng_ust_lib_ring_buffer_backend *bufb,
			      struct lttng_ust_shm_handle *handle)
{
	unsigned long sb_bindex;

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

static inline
unsigned long subbuffer_get_records_count(
				const struct lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer_backend *bufb,
				unsigned long idx,
				struct lttng_ust_shm_handle *handle)
{
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
	return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->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 lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer_backend *bufb,
				unsigned long idx,
				struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
	unsigned long overruns, sb_bindex;

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

	return overruns;
}

static inline
void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
			     struct lttng_ust_lib_ring_buffer_backend *bufb,
			     unsigned long idx,
			     unsigned long data_size,
			     struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
	pages = shmp_index(handle, bufb->array, sb_bindex);
	shmp(handle, pages->shmp)->data_size = data_size;
}

static inline
unsigned long subbuffer_get_read_data_size(
				const struct lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer_backend *bufb,
				struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
	unsigned long sb_bindex;

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

static inline
unsigned long subbuffer_get_data_size(
				const struct lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer_backend *bufb,
				unsigned long idx,
				struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
	unsigned long sb_bindex;

	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
	pages = shmp_index(handle, bufb->array, sb_bindex);
	return shmp(handle, pages->shmp)->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 lttng_ust_lib_ring_buffer_config *config,
				 struct lttng_ust_lib_ring_buffer_backend *bufb,
				 unsigned long idx,
				 struct lttng_ust_shm_handle *handle)
{
	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_index(handle, bufb->buf_wsb, idx)->id);
	for (;;) {
		/* This check is called on the fast path for each record. */
		if (caa_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_index(handle, bufb->buf_wsb, idx)->id, id, new_id);
		if (caa_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 lttng_ust_lib_ring_buffer_config *config,
				      struct lttng_ust_lib_ring_buffer_backend *bufb,
				      unsigned long idx, unsigned long offset,
				      struct lttng_ust_shm_handle *handle)
{
	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(shmp(handle, bufb->chan),
		     subbuffer_id_is_noref(config, shmp_index(handle, 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_index(handle, bufb->buf_wsb, idx)->id, offset);
}

/**
 * update_read_sb_index - Read-side subbuffer index update.
 */
static inline
int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config,
			 struct lttng_ust_lib_ring_buffer_backend *bufb,
			 struct channel_backend *chanb,
			 unsigned long consumed_idx,
			 unsigned long consumed_count,
			 struct lttng_ust_shm_handle *handle)
{
	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_index(handle, bufb->buf_wsb, consumed_idx)->id;
		if (caa_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 (caa_unlikely(!subbuffer_id_compare_offset(config, old_id,
							  consumed_count)))
			return -EAGAIN;
		CHAN_WARN_ON(shmp(handle, 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_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id,
				 bufb->buf_rsb.id);
		if (caa_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_index(handle, bufb->buf_wsb, consumed_idx)->id;
	}
	return 0;
}

#ifndef inline_memcpy
#define inline_memcpy(dest, src, n)	memcpy(dest, src, n)
#endif

/*
 * 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)

/* arch-agnostic implementation */

static inline int fls(unsigned int x)
{
	int r = 32;

	if (!x)
		return 0;
	if (!(x & 0xFFFF0000U)) {
		x <<= 16;
		r -= 16;
	}
	if (!(x & 0xFF000000U)) {
		x <<= 8;
		r -= 8;
	}
	if (!(x & 0xF0000000U)) {
		x <<= 4;
		r -= 4;
	}
	if (!(x & 0xC0000000U)) {
		x <<= 2;
		r -= 2;
	}
	if (!(x & 0x80000000U)) {
		x <<= 1;
		r -= 1;
	}
	return r;
}

static inline int get_count_order(unsigned int count)
{
	int order;

	order = fls(count) - 1;
	if (count & (count - 1))
		order++;
	return order;
}

static inline
unsigned int hweight32(unsigned int value)
{
	unsigned int r;

	r = value;
	r = r - ((r >> 1) & 0x55555555);
	r = (r & 0x33333333) + ((r >> 2) & 0x33333333);
	r += r >> 4;
	r &= 0x0F0F0F0F;
	r += r >> 8;
	r += r >> 16;
	r &= 0x000000FF;
	return r;
}

#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
4318ae1b	17	#include <lttng/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
4cfec15c	26	int lib_ring_buffer_backend_create(struct lttng_ust_lib_ring_buffer_backend *bufb,
a6352fd4	27	struct channel_backend *chan, int cpu,
38fae1d3	28	struct lttng_ust_shm_handle *handle,
1d498196	29	struct shm_object *shmobj);
852c2936	30	void channel_backend_unregister_notifiers(struct channel_backend *chanb);
4cfec15c	31	void lib_ring_buffer_backend_free(struct lttng_ust_lib_ring_buffer_backend *bufb);
852c2936 MD	32	int channel_backend_init(struct channel_backend *chanb,
852c2936 MD	33	const char *name,
4cfec15c	34	const struct lttng_ust_lib_ring_buffer_config *config,
a3f61e7f	35	size_t subbuf_size,
38fae1d3	36	size_t num_subbuf, struct lttng_ust_shm_handle *handle);
1d498196	37	void channel_backend_free(struct channel_backend *chanb,
38fae1d3	38	struct lttng_ust_shm_handle *handle);
852c2936	39
4cfec15c	40	void lib_ring_buffer_backend_reset(struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3	41	struct lttng_ust_shm_handle *handle);
852c2936 MD	42	void channel_backend_reset(struct channel_backend *chanb);
	43
	44	int lib_ring_buffer_backend_init(void);
	45	void lib_ring_buffer_backend_exit(void);
	46
4cfec15c	47	extern void _lib_ring_buffer_write(struct lttng_ust_lib_ring_buffer_backend *bufb,
852c2936 MD	48	size_t offset, const void *src, size_t len,
	49	ssize_t pagecpy);
	50
	51	/*
	52	* Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
	53	* exchanged atomically.
	54	*
	55	* Top half word, except lowest bit, belongs to "offset", which is used to keep
	56	* to count the produced buffers. For overwrite mode, this provides the
	57	* consumer with the capacity to read subbuffers in order, handling the
	58	* situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
	59	* systems) concurrently with a single execution of get_subbuf (between offset
	60	* sampling and subbuffer ID exchange).
	61	*/
	62
14641deb	63	#define HALF_ULONG_BITS (CAA_BITS_PER_LONG >> 1)
852c2936 MD	64
	65	#define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
	66	#define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
	67	#define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
	68	/*
	69	* Lowest bit of top word half belongs to noref. Used only for overwrite mode.
	70	*/
	71	#define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
	72	#define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
	73	#define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
	74	/*
	75	* In overwrite mode: lowest half of word is used for index.
	76	* Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
	77	* In producer-consumer mode: whole word used for index.
	78	*/
	79	#define SB_ID_INDEX_SHIFT 0
	80	#define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
	81	#define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
	82
	83	/*
	84	* Construct the subbuffer id from offset, index and noref. Use only the index
	85	* for producer-consumer mode (offset and noref are only used in overwrite
	86	* mode).
	87	*/
	88	static inline
4cfec15c	89	unsigned long subbuffer_id(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	90	unsigned long offset, unsigned long noref,
	91	unsigned long index)
	92	{
	93	if (config->mode == RING_BUFFER_OVERWRITE)
	94	return (offset << SB_ID_OFFSET_SHIFT)
	95	\| (noref << SB_ID_NOREF_SHIFT)
	96	\| index;
	97	else
	98	return index;
	99	}
	100
	101	/*
	102	* Compare offset with the offset contained within id. Return 1 if the offset
	103	* bits are identical, else 0.
	104	*/
	105	static inline
4cfec15c	106	int subbuffer_id_compare_offset(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	107	unsigned long id, unsigned long offset)
	108	{
	109	return (id & SB_ID_OFFSET_MASK) == (offset << SB_ID_OFFSET_SHIFT);
	110	}
	111
	112	static inline
4cfec15c	113	unsigned long subbuffer_id_get_index(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	114	unsigned long id)
	115	{
	116	if (config->mode == RING_BUFFER_OVERWRITE)
	117	return id & SB_ID_INDEX_MASK;
	118	else
	119	return id;
	120	}
	121
	122	static inline
4cfec15c	123	unsigned long subbuffer_id_is_noref(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	124	unsigned long id)
	125	{
	126	if (config->mode == RING_BUFFER_OVERWRITE)
	127	return !!(id & SB_ID_NOREF_MASK);
	128	else
	129	return 1;
	130	}
	131
	132	/*
	133	* Only used by reader on subbuffer ID it has exclusive access to. No volatile
	134	* needed.
	135	*/
	136	static inline
4cfec15c	137	void subbuffer_id_set_noref(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	138	unsigned long *id)
	139	{
	140	if (config->mode == RING_BUFFER_OVERWRITE)
	141	*id \|= SB_ID_NOREF_MASK;
	142	}
	143
	144	static inline
4cfec15c	145	void subbuffer_id_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	146	unsigned long *id, unsigned long offset)
	147	{
	148	unsigned long tmp;
	149
	150	if (config->mode == RING_BUFFER_OVERWRITE) {
	151	tmp = *id;
	152	tmp &= ~SB_ID_OFFSET_MASK;
	153	tmp \|= offset << SB_ID_OFFSET_SHIFT;
	154	tmp \|= SB_ID_NOREF_MASK;
	155	/* Volatile store, read concurrently by readers. */
14641deb	156	CMM_ACCESS_ONCE(*id) = tmp;
852c2936 MD	157	}
	158	}
	159
	160	/* No volatile access, since already used locally */
	161	static inline
4cfec15c	162	void subbuffer_id_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	163	unsigned long *id)
	164	{
	165	if (config->mode == RING_BUFFER_OVERWRITE)
	166	*id &= ~SB_ID_NOREF_MASK;
	167	}
	168
	169	/*
	170	* For overwrite mode, cap the number of subbuffers per buffer to:
	171	* 2^16 on 32-bit architectures
	172	* 2^32 on 64-bit architectures
	173	* This is required to fit in the index part of the ID. Return 0 on success,
	174	* -EPERM on failure.
	175	*/
	176	static inline
4cfec15c	177	int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *config,
852c2936 MD	178	unsigned long num_subbuf)
	179	{
	180	if (config->mode == RING_BUFFER_OVERWRITE)
	181	return (num_subbuf > (1UL << HALF_ULONG_BITS)) ? -EPERM : 0;
	182	else
	183	return 0;
	184	}
	185
	186	static inline
4cfec15c MD	187	void subbuffer_count_record(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	188	struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3	189	unsigned long idx, struct lttng_ust_shm_handle *handle)
852c2936 MD	190	{
	191	unsigned long sb_bindex;
	192
4746ae29 MD	193	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
4746ae29 MD	194	v_inc(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
852c2936 MD	195	}
	196
	197	/*
	198	* Reader has exclusive subbuffer access for record consumption. No need to
	199	* perform the decrement atomically.
	200	*/
	201	static inline
4cfec15c MD	202	void subbuffer_consume_record(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	203	struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3	204	struct lttng_ust_shm_handle *handle)
852c2936 MD	205	{
	206	unsigned long sb_bindex;
	207
	208	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
1d498196	209	CHAN_WARN_ON(shmp(handle, bufb->chan),
4746ae29	210	!v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread));
852c2936	211	/* Non-atomic decrement protected by exclusive subbuffer access */
4746ae29	212	_v_dec(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_unread);
852c2936 MD	213	v_inc(config, &bufb->records_read);
	214	}
	215
	216	static inline
	217	unsigned long subbuffer_get_records_count(
4cfec15c MD	218	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	219	struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	220	unsigned long idx,
38fae1d3	221	struct lttng_ust_shm_handle *handle)
852c2936 MD	222	{
	223	unsigned long sb_bindex;
	224
4746ae29 MD	225	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
4746ae29 MD	226	return v_read(config, &shmp(handle, shmp_index(handle, bufb->array, sb_bindex)->shmp)->records_commit);
852c2936 MD	227	}
	228
	229	/*
	230	* Must be executed at subbuffer delivery when the writer has _exclusive_
	231	* subbuffer access. See ring_buffer_check_deliver() for details.
	232	* ring_buffer_get_records_count() must be called to get the records count
	233	* before this function, because it resets the records_commit count.
	234	*/
	235	static inline
	236	unsigned long subbuffer_count_records_overrun(
4cfec15c MD	237	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	238	struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	239	unsigned long idx,
38fae1d3	240	struct lttng_ust_shm_handle *handle)
852c2936	241	{
4cfec15c	242	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
852c2936 MD	243	unsigned long overruns, sb_bindex;
852c2936 MD	244
4746ae29 MD	245	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
4746ae29 MD	246	pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196 MD	247	overruns = v_read(config, &shmp(handle, pages->shmp)->records_unread);
	248	v_set(config, &shmp(handle, pages->shmp)->records_unread,
	249	v_read(config, &shmp(handle, pages->shmp)->records_commit));
	250	v_set(config, &shmp(handle, pages->shmp)->records_commit, 0);
852c2936 MD	251
	252	return overruns;
	253	}
	254
	255	static inline
4cfec15c MD	256	void subbuffer_set_data_size(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	257	struct lttng_ust_lib_ring_buffer_backend *bufb,
852c2936	258	unsigned long idx,
1d498196	259	unsigned long data_size,
38fae1d3	260	struct lttng_ust_shm_handle *handle)
852c2936	261	{
4cfec15c	262	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
852c2936 MD	263	unsigned long sb_bindex;
852c2936 MD	264
4746ae29 MD	265	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
4746ae29 MD	266	pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196	267	shmp(handle, pages->shmp)->data_size = data_size;
852c2936 MD	268	}
	269
	270	static inline
	271	unsigned long subbuffer_get_read_data_size(
4cfec15c MD	272	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	273	struct lttng_ust_lib_ring_buffer_backend *bufb,
38fae1d3	274	struct lttng_ust_shm_handle *handle)
852c2936	275	{
4cfec15c	276	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
852c2936 MD	277	unsigned long sb_bindex;
	278
	279	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
4746ae29	280	pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196	281	return shmp(handle, pages->shmp)->data_size;
852c2936 MD	282	}
	283
	284	static inline
	285	unsigned long subbuffer_get_data_size(
4cfec15c MD	286	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	287	struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	288	unsigned long idx,
38fae1d3	289	struct lttng_ust_shm_handle *handle)
852c2936	290	{
4cfec15c	291	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
852c2936 MD	292	unsigned long sb_bindex;
852c2936 MD	293
4746ae29 MD	294	sb_bindex = subbuffer_id_get_index(config, shmp_index(handle, bufb->buf_wsb, idx)->id);
4746ae29 MD	295	pages = shmp_index(handle, bufb->array, sb_bindex);
1d498196	296	return shmp(handle, pages->shmp)->data_size;
852c2936 MD	297	}
	298
	299	/**
	300	* lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
	301	* writer.
	302	*/
	303	static inline
4cfec15c MD	304	void lib_ring_buffer_clear_noref(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	305	struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	306	unsigned long idx,
38fae1d3	307	struct lttng_ust_shm_handle *handle)
852c2936 MD	308	{
	309	unsigned long id, new_id;
	310
	311	if (config->mode != RING_BUFFER_OVERWRITE)
	312	return;
	313
	314	/*
	315	* Performing a volatile access to read the sb_pages, because we want to
	316	* read a coherent version of the pointer and the associated noref flag.
	317	*/
4746ae29	318	id = CMM_ACCESS_ONCE(shmp_index(handle, bufb->buf_wsb, idx)->id);
852c2936 MD	319	for (;;) {
852c2936 MD	320	/* This check is called on the fast path for each record. */
b5a3dfa5	321	if (caa_likely(!subbuffer_id_is_noref(config, id))) {
852c2936 MD	322	/*
	323	* Store after load dependency ordering the writes to
	324	* the subbuffer after load and test of the noref flag
	325	* matches the memory barrier implied by the cmpxchg()
	326	* in update_read_sb_index().
	327	*/
	328	return; /* Already writing to this buffer */
	329	}
	330	new_id = id;
	331	subbuffer_id_clear_noref(config, &new_id);
4746ae29	332	new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, idx)->id, id, new_id);
b5a3dfa5	333	if (caa_likely(new_id == id))
852c2936 MD	334	break;
	335	id = new_id;
	336	}
	337	}
	338
	339	/**
	340	* lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
	341	* called by writer.
	342	*/
	343	static inline
4cfec15c MD	344	void lib_ring_buffer_set_noref_offset(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	345	struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	346	unsigned long idx, unsigned long offset,
38fae1d3	347	struct lttng_ust_shm_handle *handle)
852c2936 MD	348	{
	349	if (config->mode != RING_BUFFER_OVERWRITE)
	350	return;
	351
	352	/*
	353	* Because ring_buffer_set_noref() is only called by a single thread
	354	* (the one which updated the cc_sb value), there are no concurrent
	355	* updates to take care of: other writers have not updated cc_sb, so
	356	* they cannot set the noref flag, and concurrent readers cannot modify
	357	* the pointer because the noref flag is not set yet.
	358	* The smp_wmb() in ring_buffer_commit() takes care of ordering writes
	359	* to the subbuffer before this set noref operation.
	360	* subbuffer_set_noref() uses a volatile store to deal with concurrent
	361	* readers of the noref flag.
	362	*/
1d498196	363	CHAN_WARN_ON(shmp(handle, bufb->chan),
4746ae29	364	subbuffer_id_is_noref(config, shmp_index(handle, bufb->buf_wsb, idx)->id));
852c2936 MD	365	/*
	366	* Memory barrier that ensures counter stores are ordered before set
	367	* noref and offset.
	368	*/
14641deb	369	cmm_smp_mb();
4746ae29	370	subbuffer_id_set_noref_offset(config, &shmp_index(handle, bufb->buf_wsb, idx)->id, offset);
852c2936 MD	371	}
	372
	373	/**
	374	* update_read_sb_index - Read-side subbuffer index update.
	375	*/
	376	static inline
4cfec15c MD	377	int update_read_sb_index(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	378	struct lttng_ust_lib_ring_buffer_backend *bufb,
852c2936 MD	379	struct channel_backend *chanb,
852c2936 MD	380	unsigned long consumed_idx,
1d498196	381	unsigned long consumed_count,
38fae1d3	382	struct lttng_ust_shm_handle *handle)
852c2936 MD	383	{
	384	unsigned long old_id, new_id;
	385
	386	if (config->mode == RING_BUFFER_OVERWRITE) {
	387	/*
	388	* Exchange the target writer subbuffer with our own unused
14641deb	389	* subbuffer. No need to use CMM_ACCESS_ONCE() here to read the
852c2936 MD	390	* old_wpage, because the value read will be confirmed by the
	391	* following cmpxchg().
	392	*/
4746ae29	393	old_id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
b5a3dfa5	394	if (caa_unlikely(!subbuffer_id_is_noref(config, old_id)))
852c2936 MD	395	return -EAGAIN;
	396	/*
	397	* Make sure the offset count we are expecting matches the one
	398	* indicated by the writer.
	399	*/
b5a3dfa5	400	if (caa_unlikely(!subbuffer_id_compare_offset(config, old_id,
852c2936 MD	401	consumed_count)))
852c2936 MD	402	return -EAGAIN;
1d498196	403	CHAN_WARN_ON(shmp(handle, bufb->chan),
852c2936 MD	404	!subbuffer_id_is_noref(config, bufb->buf_rsb.id));
	405	subbuffer_id_set_noref_offset(config, &bufb->buf_rsb.id,
	406	consumed_count);
4746ae29	407	new_id = uatomic_cmpxchg(&shmp_index(handle, bufb->buf_wsb, consumed_idx)->id, old_id,
852c2936	408	bufb->buf_rsb.id);
b5a3dfa5	409	if (caa_unlikely(old_id != new_id))
852c2936 MD	410	return -EAGAIN;
	411	bufb->buf_rsb.id = new_id;
	412	} else {
	413	/* No page exchange, use the writer page directly */
4746ae29	414	bufb->buf_rsb.id = shmp_index(handle, bufb->buf_wsb, consumed_idx)->id;
852c2936 MD	415	}
	416	return 0;
	417	}
	418
0d4aa2df MD	419	#ifndef inline_memcpy
	420	#define inline_memcpy(dest, src, n) memcpy(dest, src, n)
	421	#endif
	422
852c2936 MD	423	/*
	424	* Use the architecture-specific memcpy implementation for constant-sized
	425	* inputs, but rely on an inline memcpy for length statically unknown.
	426	* The function call to memcpy is just way too expensive for a fast path.
	427	*/
	428	#define lib_ring_buffer_do_copy(config, dest, src, len) \
	429	do { \
	430	size_t __len = (len); \
	431	if (__builtin_constant_p(len)) \
	432	memcpy(dest, src, __len); \
	433	else \
	434	inline_memcpy(dest, src, __len); \
	435	} while (0)
	436
b728d87e MD	437	/* arch-agnostic implementation */
	438
	439	static inline int fls(unsigned int x)
	440	{
	441	int r = 32;
	442
	443	if (!x)
	444	return 0;
	445	if (!(x & 0xFFFF0000U)) {
	446	x <<= 16;
	447	r -= 16;
	448	}
	449	if (!(x & 0xFF000000U)) {
	450	x <<= 8;
	451	r -= 8;
	452	}
	453	if (!(x & 0xF0000000U)) {
	454	x <<= 4;
	455	r -= 4;
	456	}
	457	if (!(x & 0xC0000000U)) {
	458	x <<= 2;
	459	r -= 2;
	460	}
	461	if (!(x & 0x80000000U)) {
	462	x <<= 1;
	463	r -= 1;
	464	}
	465	return r;
	466	}
	467
	468	static inline int get_count_order(unsigned int count)
	469	{
	470	int order;
	471
	472	order = fls(count) - 1;
	473	if (count & (count - 1))
	474	order++;
	475	return order;
	476	}
	477
35897f8b MD	478	static inline
	479	unsigned int hweight32(unsigned int value)
	480	{
	481	unsigned int r;
	482
	483	r = value;
	484	r = r - ((r >> 1) & 0x55555555);
	485	r = (r & 0x33333333) + ((r >> 2) & 0x33333333);
	486	r += r >> 4;
	487	r &= 0x0F0F0F0F;
	488	r += r >> 8;
	489	r += r >> 16;
	490	r &= 0x000000FF;
	491	return r;
	492	}
	493
852c2936	494	#endif /* _LINUX_RING_BUFFER_BACKEND_INTERNAL_H */