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

/*
 * SPDX-License-Identifier: LGPL-2.1-only
 *
 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * Ring buffer backend (API).
 *
 * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
 * the reader in flight recorder mode.
 */

#ifndef _LTTNG_RING_BUFFER_BACKEND_H
#define _LTTNG_RING_BUFFER_BACKEND_H

#include <stddef.h>
#include <unistd.h>

/* Internal helpers */
#include "backend_internal.h"
#include "frontend_internal.h"

/* Ring buffer backend API */

/* Ring buffer backend access (read/write) */

extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb,
				   size_t offset, void *dest, size_t len,
				   struct lttng_ust_shm_handle *handle)
	__attribute__((visibility("hidden")));

extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
				     size_t offset, void *dest, size_t len,
				     struct lttng_ust_shm_handle *handle)
	__attribute__((visibility("hidden")));

/*
 * Return the address where a given offset is located.
 * Should be used to get the current subbuffer header pointer. Given we know
 * it's never on a page boundary, it's safe to write directly to this address,
 * as long as the write is never bigger than a page size.
 */
extern void *
lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
			       size_t offset,
			       struct lttng_ust_shm_handle *handle)
	__attribute__((visibility("hidden")));

extern void *
lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
				    size_t offset,
				    struct lttng_ust_shm_handle *handle)
	__attribute__((visibility("hidden")));

/**
 * lib_ring_buffer_write - write data to a buffer backend
 * @config : ring buffer instance configuration
 * @ctx: ring buffer context. (input arguments only)
 * @src : source pointer to copy from
 * @len : length of data to copy
 *
 * This function copies "len" bytes of data from a source pointer to a buffer
 * backend, at the current context offset. This is more or less a buffer
 * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
 * if copy is crossing a page boundary.
 */
static inline __attribute__((always_inline))
void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
			   struct lttng_ust_lib_ring_buffer_ctx *ctx,
			   const void *src, size_t len)
{
	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	struct channel_backend *chanb = &ctx_private->chan->backend;
	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
	size_t offset = ctx_private->buf_offset;
	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	void *p;

	if (caa_unlikely(!len))
		return;
	/*
	 * Underlying layer should never ask for writes across
	 * subbuffers.
	 */
	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	if (caa_unlikely(!backend_pages)) {
		if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
			return;
	}
	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	if (caa_unlikely(!p))
		return;
	lib_ring_buffer_do_copy(config, p, src, len);
	ctx_private->buf_offset += len;
}

/*
 * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 * terminating character is found in @src. Returns the number of bytes
 * copied. Does *not* terminate @dest with NULL terminating character.
 */
static inline __attribute__((always_inline))
size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
		char *dest, const char *src, size_t len)
{
	size_t count;

	for (count = 0; count < len; count++) {
		char c;

		/*
		 * Only read source character once, in case it is
		 * modified concurrently.
		 */
		c = CMM_LOAD_SHARED(src[count]);
		if (!c)
			break;
		lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
	}
	return count;
}

/**
 * lib_ring_buffer_strcpy - write string data to a buffer backend
 * @config : ring buffer instance configuration
 * @ctx: ring buffer context. (input arguments only)
 * @src : source pointer to copy from
 * @len : length of data to copy
 * @pad : character to use for padding
 *
 * This function copies @len - 1 bytes of string data from a source
 * pointer to a buffer backend, followed by a terminating '\0'
 * character, at the current context offset. This is more or less a
 * buffer backend-specific strncpy() operation. If a terminating '\0'
 * character is found in @src before @len - 1 characters are copied, pad
 * the buffer with @pad characters (e.g. '#').
 */
static inline __attribute__((always_inline))
void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
			   struct lttng_ust_lib_ring_buffer_ctx *ctx,
			   const char *src, size_t len, char pad)
{
	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	struct channel_backend *chanb = &ctx_private->chan->backend;
	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
	size_t count;
	size_t offset = ctx_private->buf_offset;
	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	void *p;

	if (caa_unlikely(!len))
		return;
	/*
	 * Underlying layer should never ask for writes across
	 * subbuffers.
	 */
	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	if (caa_unlikely(!backend_pages)) {
		if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
			return;
	}
	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	if (caa_unlikely(!p))
		return;

	count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
	offset += count;
	/* Padding */
	if (caa_unlikely(count < len - 1)) {
		size_t pad_len = len - 1 - count;

		p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
		if (caa_unlikely(!p))
			return;
		lib_ring_buffer_do_memset(p, pad, pad_len);
		offset += pad_len;
	}
	/* Final '\0' */
	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	if (caa_unlikely(!p))
		return;
	lib_ring_buffer_do_memset(p, '\0', 1);
	ctx_private->buf_offset += len;
}

/**
 * lib_ring_buffer_pstrcpy - write to a buffer backend P-string
 * @config : ring buffer instance configuration
 * @ctx: ring buffer context. (input arguments only)
 * @src : source pointer to copy from
 * @len : length of data to copy
 * @pad : character to use for padding
 *
 * This function copies up to @len bytes of data from a source pointer
 * to a Pascal String into the buffer backend. If a terminating '\0'
 * character is found in @src before @len characters are copied, pad the
 * buffer with @pad characters (e.g.  '\0').
 *
 * The length of the pascal strings in the ring buffer is explicit: it
 * is either the array or sequence length.
 */
static inline __attribute__((always_inline))
void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
			   struct lttng_ust_lib_ring_buffer_ctx *ctx,
			   const char *src, size_t len, char pad)
{
	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	struct channel_backend *chanb = &ctx_private->chan->backend;
	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
	size_t count;
	size_t offset = ctx_private->buf_offset;
	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	void *p;

	if (caa_unlikely(!len))
		return;
	/*
	 * Underlying layer should never ask for writes across
	 * subbuffers.
	 */
	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	if (caa_unlikely(!backend_pages)) {
		if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
			return;
	}
	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	if (caa_unlikely(!p))
		return;

	count = lib_ring_buffer_do_strcpy(config, p, src, len);
	offset += count;
	/* Padding */
	if (caa_unlikely(count < len)) {
		size_t pad_len = len - count;

		p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
		if (caa_unlikely(!p))
			return;
		lib_ring_buffer_do_memset(p, pad, pad_len);
	}
	ctx_private->buf_offset += len;
}

/*
 * This accessor counts the number of unread records in a buffer.
 * It only provides a consistent value if no reads not writes are performed
 * concurrently.
 */
static inline
unsigned long lib_ring_buffer_get_records_unread(
				const struct lttng_ust_lib_ring_buffer_config *config,
				struct lttng_ust_lib_ring_buffer *buf,
				struct lttng_ust_shm_handle *handle)
{
	struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
	unsigned long records_unread = 0, sb_bindex;
	unsigned int i;
	struct lttng_ust_lib_ring_buffer_channel *chan;

	chan = shmp(handle, bufb->chan);
	if (!chan)
		return 0;
	for (i = 0; i < chan->backend.num_subbuf; i++) {
		struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
		struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
		struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;

		wsb = shmp_index(handle, bufb->buf_wsb, i);
		if (!wsb)
			return 0;
		sb_bindex = subbuffer_id_get_index(config, wsb->id);
		rpages = shmp_index(handle, bufb->array, sb_bindex);
		if (!rpages)
			return 0;
		backend_pages = shmp(handle, rpages->shmp);
		if (!backend_pages)
			return 0;
		records_unread += v_read(config, &backend_pages->records_unread);
	}
	if (config->mode == RING_BUFFER_OVERWRITE) {
		struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
		struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;

		sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
		rpages = shmp_index(handle, bufb->array, sb_bindex);
		if (!rpages)
			return 0;
		backend_pages = shmp(handle, rpages->shmp);
		if (!backend_pages)
			return 0;
		records_unread += v_read(config, &backend_pages->records_unread);
	}
	return records_unread;
}

#endif /* _LTTNG_RING_BUFFER_BACKEND_H */
Commit	Line	Data
852c2936	1	/*
c0c0989a	2	* SPDX-License-Identifier: LGPL-2.1-only
852c2936	3	*
e92f3e28 MD	4	* Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
e92f3e28 MD	5	*
c0c0989a	6	* Ring buffer backend (API).
852c2936 MD	7	*
	8	* Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
	9	* the reader in flight recorder mode.
	10	*/
	11
c0c0989a MJ	12	#ifndef _LTTNG_RING_BUFFER_BACKEND_H
	13	#define _LTTNG_RING_BUFFER_BACKEND_H
	14
b4051ad8	15	#include <stddef.h>
14641deb MD	16	#include <unistd.h>
14641deb MD	17
852c2936	18	/* Internal helpers */
4931a13e MD	19	#include "backend_internal.h"
4931a13e MD	20	#include "frontend_internal.h"
852c2936 MD	21
	22	/* Ring buffer backend API */
	23
	24	/* Ring buffer backend access (read/write) */
	25
4cfec15c	26	extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	27	size_t offset, void *dest, size_t len,
1d18d519 MJ	28	struct lttng_ust_shm_handle *handle)
1d18d519 MJ	29	__attribute__((visibility("hidden")));
852c2936	30
4cfec15c	31	extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	32	size_t offset, void *dest, size_t len,
1d18d519 MJ	33	struct lttng_ust_shm_handle *handle)
1d18d519 MJ	34	__attribute__((visibility("hidden")));
852c2936	35
852c2936 MD	36	/*
	37	* Return the address where a given offset is located.
	38	* Should be used to get the current subbuffer header pointer. Given we know
	39	* it's never on a page boundary, it's safe to write directly to this address,
	40	* as long as the write is never bigger than a page size.
	41	*/
	42	extern void *
4cfec15c	43	lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	44	size_t offset,
1d18d519 MJ	45	struct lttng_ust_shm_handle *handle)
1d18d519 MJ	46	__attribute__((visibility("hidden")));
ddabe860	47
852c2936	48	extern void *
4cfec15c	49	lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	50	size_t offset,
1d18d519 MJ	51	struct lttng_ust_shm_handle *handle)
1d18d519 MJ	52	__attribute__((visibility("hidden")));
852c2936 MD	53
	54	/**
	55	* lib_ring_buffer_write - write data to a buffer backend
	56	* @config : ring buffer instance configuration
	57	* @ctx: ring buffer context. (input arguments only)
	58	* @src : source pointer to copy from
	59	* @len : length of data to copy
	60	*
	61	* This function copies "len" bytes of data from a source pointer to a buffer
	62	* backend, at the current context offset. This is more or less a buffer
	63	* backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
	64	* if copy is crossing a page boundary.
	65	*/
00d0f8eb	66	static inline __attribute__((always_inline))
4cfec15c MD	67	void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	68	struct lttng_ust_lib_ring_buffer_ctx *ctx,
852c2936 MD	69	const void *src, size_t len)
852c2936 MD	70	{
8936b6c0 MD	71	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	72	struct channel_backend *chanb = &ctx_private->chan->backend;
	73	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
	74	size_t offset = ctx_private->buf_offset;
15500a1b MD	75	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
15500a1b MD	76	void *p;
852c2936	77
0bf3c920 MD	78	if (caa_unlikely(!len))
0bf3c920 MD	79	return;
a6352fd4 MD	80	/*
	81	* Underlying layer should never ask for writes across
	82	* subbuffers.
	83	*/
a3492932 MD	84	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	85	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	86	if (caa_unlikely(!backend_pages)) {
	87	if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
	88	return;
	89	}
15500a1b MD	90	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	91	if (caa_unlikely(!p))
	92	return;
	93	lib_ring_buffer_do_copy(config, p, src, len);
8936b6c0	94	ctx_private->buf_offset += len;
852c2936 MD	95	}
852c2936 MD	96
a44c74d9 MD	97	/*
	98	* Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
	99	* terminating character is found in @src. Returns the number of bytes
	100	* copied. Does not terminate @dest with NULL terminating character.
	101	*/
00d0f8eb	102	static inline __attribute__((always_inline))
a44c74d9 MD	103	size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
	104	char dest, const char src, size_t len)
	105	{
	106	size_t count;
	107
	108	for (count = 0; count < len; count++) {
	109	char c;
	110
	111	/*
	112	* Only read source character once, in case it is
	113	* modified concurrently.
	114	*/
	115	c = CMM_LOAD_SHARED(src[count]);
	116	if (!c)
	117	break;
	118	lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
	119	}
	120	return count;
	121	}
	122
	123	/**
	124	* lib_ring_buffer_strcpy - write string data to a buffer backend
	125	* @config : ring buffer instance configuration
	126	* @ctx: ring buffer context. (input arguments only)
	127	* @src : source pointer to copy from
	128	* @len : length of data to copy
	129	* @pad : character to use for padding
	130	*
	131	* This function copies @len - 1 bytes of string data from a source
	132	* pointer to a buffer backend, followed by a terminating '\0'
	133	* character, at the current context offset. This is more or less a
	134	* buffer backend-specific strncpy() operation. If a terminating '\0'
	135	* character is found in @src before @len - 1 characters are copied, pad
	136	* the buffer with @pad characters (e.g. '#').
	137	*/
00d0f8eb	138	static inline __attribute__((always_inline))
a44c74d9 MD	139	void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
a44c74d9 MD	140	struct lttng_ust_lib_ring_buffer_ctx *ctx,
b4c8bf2f	141	const char *src, size_t len, char pad)
a44c74d9	142	{
8936b6c0 MD	143	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	144	struct channel_backend *chanb = &ctx_private->chan->backend;
	145	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
a3492932	146	size_t count;
8936b6c0	147	size_t offset = ctx_private->buf_offset;
a3492932 MD	148	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
a3492932 MD	149	void *p;
a44c74d9 MD	150
	151	if (caa_unlikely(!len))
	152	return;
a44c74d9 MD	153	/*
	154	* Underlying layer should never ask for writes across
	155	* subbuffers.
	156	*/
a3492932 MD	157	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	158	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	159	if (caa_unlikely(!backend_pages)) {
	160	if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
	161	return;
	162	}
	163	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	164	if (caa_unlikely(!p))
	165	return;
	166
	167	count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
a44c74d9 MD	168	offset += count;
	169	/* Padding */
	170	if (caa_unlikely(count < len - 1)) {
	171	size_t pad_len = len - 1 - count;
	172
a3492932 MD	173	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	174	if (caa_unlikely(!p))
	175	return;
	176	lib_ring_buffer_do_memset(p, pad, pad_len);
a44c74d9 MD	177	offset += pad_len;
	178	}
	179	/* Final '\0' */
a3492932 MD	180	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	181	if (caa_unlikely(!p))
	182	return;
	183	lib_ring_buffer_do_memset(p, '\0', 1);
8936b6c0	184	ctx_private->buf_offset += len;
a44c74d9 MD	185	}
a44c74d9 MD	186
879f9b0a MD	187	/**
	188	* lib_ring_buffer_pstrcpy - write to a buffer backend P-string
	189	* @config : ring buffer instance configuration
	190	* @ctx: ring buffer context. (input arguments only)
	191	* @src : source pointer to copy from
	192	* @len : length of data to copy
	193	* @pad : character to use for padding
	194	*
	195	* This function copies up to @len bytes of data from a source pointer
	196	* to a Pascal String into the buffer backend. If a terminating '\0'
	197	* character is found in @src before @len characters are copied, pad the
	198	* buffer with @pad characters (e.g. '\0').
	199	*
	200	* The length of the pascal strings in the ring buffer is explicit: it
	201	* is either the array or sequence length.
	202	*/
	203	static inline __attribute__((always_inline))
	204	void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
	205	struct lttng_ust_lib_ring_buffer_ctx *ctx,
	206	const char *src, size_t len, char pad)
	207	{
8936b6c0 MD	208	struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
	209	struct channel_backend *chanb = &ctx_private->chan->backend;
	210	struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
879f9b0a	211	size_t count;
8936b6c0	212	size_t offset = ctx_private->buf_offset;
879f9b0a MD	213	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	214	void *p;
	215
	216	if (caa_unlikely(!len))
	217	return;
	218	/*
	219	* Underlying layer should never ask for writes across
	220	* subbuffers.
	221	*/
	222	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	223	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	224	if (caa_unlikely(!backend_pages)) {
	225	if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
	226	return;
	227	}
	228	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	229	if (caa_unlikely(!p))
	230	return;
	231
	232	count = lib_ring_buffer_do_strcpy(config, p, src, len);
	233	offset += count;
	234	/* Padding */
	235	if (caa_unlikely(count < len)) {
	236	size_t pad_len = len - count;
	237
	238	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	239	if (caa_unlikely(!p))
	240	return;
	241	lib_ring_buffer_do_memset(p, pad, pad_len);
	242	}
8936b6c0	243	ctx_private->buf_offset += len;
879f9b0a MD	244	}
879f9b0a MD	245
852c2936 MD	246	/*
	247	* This accessor counts the number of unread records in a buffer.
	248	* It only provides a consistent value if no reads not writes are performed
	249	* concurrently.
	250	*/
	251	static inline
	252	unsigned long lib_ring_buffer_get_records_unread(
4cfec15c MD	253	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	254	struct lttng_ust_lib_ring_buffer *buf,
38fae1d3	255	struct lttng_ust_shm_handle *handle)
852c2936	256	{
4cfec15c	257	struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
15500a1b	258	unsigned long records_unread = 0, sb_bindex;
852c2936	259	unsigned int i;
5198080d	260	struct lttng_ust_lib_ring_buffer_channel *chan;
852c2936	261
15500a1b MD	262	chan = shmp(handle, bufb->chan);
	263	if (!chan)
	264	return 0;
	265	for (i = 0; i < chan->backend.num_subbuf; i++) {
	266	struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
	267	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
	268	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	269
	270	wsb = shmp_index(handle, bufb->buf_wsb, i);
	271	if (!wsb)
	272	return 0;
	273	sb_bindex = subbuffer_id_get_index(config, wsb->id);
	274	rpages = shmp_index(handle, bufb->array, sb_bindex);
	275	if (!rpages)
	276	return 0;
	277	backend_pages = shmp(handle, rpages->shmp);
	278	if (!backend_pages)
	279	return 0;
	280	records_unread += v_read(config, &backend_pages->records_unread);
852c2936 MD	281	}
852c2936 MD	282	if (config->mode == RING_BUFFER_OVERWRITE) {
15500a1b MD	283	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
	284	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	285
	286	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
	287	rpages = shmp_index(handle, bufb->array, sb_bindex);
	288	if (!rpages)
	289	return 0;
	290	backend_pages = shmp(handle, rpages->shmp);
	291	if (!backend_pages)
	292	return 0;
	293	records_unread += v_read(config, &backend_pages->records_unread);
852c2936 MD	294	}
	295	return records_unread;
	296	}
	297
e92f3e28	298	#endif /* _LTTNG_RING_BUFFER_BACKEND_H */