[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);

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);

/*
 * 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);
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);

/**
 * 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 channel_backend *chanb = &ctx->chan->backend;
	struct lttng_ust_shm_handle *handle = ctx->handle;
	size_t offset = ctx->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->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, int pad)
{
	struct channel_backend *chanb = &ctx->chan->backend;
	struct lttng_ust_shm_handle *handle = ctx->handle;
	size_t count;
	size_t offset = ctx->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->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 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,
38fae1d3	28	struct lttng_ust_shm_handle *handle);
852c2936	29
4cfec15c	30	extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	31	size_t offset, void *dest, size_t len,
38fae1d3	32	struct lttng_ust_shm_handle *handle);
852c2936	33
852c2936 MD	34	/*
	35	* Return the address where a given offset is located.
	36	* Should be used to get the current subbuffer header pointer. Given we know
	37	* it's never on a page boundary, it's safe to write directly to this address,
	38	* as long as the write is never bigger than a page size.
	39	*/
	40	extern void *
4cfec15c	41	lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	42	size_t offset,
38fae1d3	43	struct lttng_ust_shm_handle *handle);
852c2936	44	extern void *
4cfec15c	45	lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
1d498196	46	size_t offset,
38fae1d3	47	struct lttng_ust_shm_handle *handle);
852c2936 MD	48
	49	/**
	50	* lib_ring_buffer_write - write data to a buffer backend
	51	* @config : ring buffer instance configuration
	52	* @ctx: ring buffer context. (input arguments only)
	53	* @src : source pointer to copy from
	54	* @len : length of data to copy
	55	*
	56	* This function copies "len" bytes of data from a source pointer to a buffer
	57	* backend, at the current context offset. This is more or less a buffer
	58	* backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
	59	* if copy is crossing a page boundary.
	60	*/
00d0f8eb	61	static inline __attribute__((always_inline))
4cfec15c MD	62	void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	63	struct lttng_ust_lib_ring_buffer_ctx *ctx,
852c2936 MD	64	const void *src, size_t len)
852c2936 MD	65	{
852c2936	66	struct channel_backend *chanb = &ctx->chan->backend;
38fae1d3	67	struct lttng_ust_shm_handle *handle = ctx->handle;
852c2936	68	size_t offset = ctx->buf_offset;
15500a1b MD	69	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
15500a1b MD	70	void *p;
852c2936	71
0bf3c920 MD	72	if (caa_unlikely(!len))
0bf3c920 MD	73	return;
a6352fd4 MD	74	/*
	75	* Underlying layer should never ask for writes across
	76	* subbuffers.
	77	*/
a3492932 MD	78	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	79	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	80	if (caa_unlikely(!backend_pages)) {
	81	if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
	82	return;
	83	}
15500a1b MD	84	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	85	if (caa_unlikely(!p))
	86	return;
	87	lib_ring_buffer_do_copy(config, p, src, len);
852c2936 MD	88	ctx->buf_offset += len;
	89	}
	90
a44c74d9 MD	91	/*
	92	* Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
	93	* terminating character is found in @src. Returns the number of bytes
	94	* copied. Does not terminate @dest with NULL terminating character.
	95	*/
00d0f8eb	96	static inline __attribute__((always_inline))
a44c74d9 MD	97	size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
	98	char dest, const char src, size_t len)
	99	{
	100	size_t count;
	101
	102	for (count = 0; count < len; count++) {
	103	char c;
	104
	105	/*
	106	* Only read source character once, in case it is
	107	* modified concurrently.
	108	*/
	109	c = CMM_LOAD_SHARED(src[count]);
	110	if (!c)
	111	break;
	112	lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
	113	}
	114	return count;
	115	}
	116
	117	/**
	118	* lib_ring_buffer_strcpy - write string data to a buffer backend
	119	* @config : ring buffer instance configuration
	120	* @ctx: ring buffer context. (input arguments only)
	121	* @src : source pointer to copy from
	122	* @len : length of data to copy
	123	* @pad : character to use for padding
	124	*
	125	* This function copies @len - 1 bytes of string data from a source
	126	* pointer to a buffer backend, followed by a terminating '\0'
	127	* character, at the current context offset. This is more or less a
	128	* buffer backend-specific strncpy() operation. If a terminating '\0'
	129	* character is found in @src before @len - 1 characters are copied, pad
	130	* the buffer with @pad characters (e.g. '#').
	131	*/
00d0f8eb	132	static inline __attribute__((always_inline))
a44c74d9 MD	133	void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
	134	struct lttng_ust_lib_ring_buffer_ctx *ctx,
	135	const char *src, size_t len, int pad)
	136	{
a44c74d9 MD	137	struct channel_backend *chanb = &ctx->chan->backend;
a44c74d9 MD	138	struct lttng_ust_shm_handle *handle = ctx->handle;
a3492932	139	size_t count;
a44c74d9	140	size_t offset = ctx->buf_offset;
a3492932 MD	141	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
a3492932 MD	142	void *p;
a44c74d9 MD	143
	144	if (caa_unlikely(!len))
	145	return;
a44c74d9 MD	146	/*
	147	* Underlying layer should never ask for writes across
	148	* subbuffers.
	149	*/
a3492932 MD	150	CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
	151	backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
	152	if (caa_unlikely(!backend_pages)) {
	153	if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
	154	return;
	155	}
	156	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	157	if (caa_unlikely(!p))
	158	return;
	159
	160	count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
a44c74d9 MD	161	offset += count;
	162	/* Padding */
	163	if (caa_unlikely(count < len - 1)) {
	164	size_t pad_len = len - 1 - count;
	165
a3492932 MD	166	p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
	167	if (caa_unlikely(!p))
	168	return;
	169	lib_ring_buffer_do_memset(p, pad, pad_len);
a44c74d9 MD	170	offset += pad_len;
	171	}
	172	/* Final '\0' */
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, '\0', 1);
a44c74d9 MD	177	ctx->buf_offset += len;
	178	}
	179
852c2936 MD	180	/*
	181	* This accessor counts the number of unread records in a buffer.
	182	* It only provides a consistent value if no reads not writes are performed
	183	* concurrently.
	184	*/
	185	static inline
	186	unsigned long lib_ring_buffer_get_records_unread(
4cfec15c MD	187	const struct lttng_ust_lib_ring_buffer_config *config,
4cfec15c MD	188	struct lttng_ust_lib_ring_buffer *buf,
38fae1d3	189	struct lttng_ust_shm_handle *handle)
852c2936	190	{
4cfec15c	191	struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
15500a1b	192	unsigned long records_unread = 0, sb_bindex;
852c2936	193	unsigned int i;
15500a1b	194	struct channel *chan;
852c2936	195
15500a1b MD	196	chan = shmp(handle, bufb->chan);
	197	if (!chan)
	198	return 0;
	199	for (i = 0; i < chan->backend.num_subbuf; i++) {
	200	struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
	201	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
	202	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	203
	204	wsb = shmp_index(handle, bufb->buf_wsb, i);
	205	if (!wsb)
	206	return 0;
	207	sb_bindex = subbuffer_id_get_index(config, wsb->id);
	208	rpages = shmp_index(handle, bufb->array, sb_bindex);
	209	if (!rpages)
	210	return 0;
	211	backend_pages = shmp(handle, rpages->shmp);
	212	if (!backend_pages)
	213	return 0;
	214	records_unread += v_read(config, &backend_pages->records_unread);
852c2936 MD	215	}
852c2936 MD	216	if (config->mode == RING_BUFFER_OVERWRITE) {
15500a1b MD	217	struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
	218	struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
	219
	220	sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
	221	rpages = shmp_index(handle, bufb->array, sb_bindex);
	222	if (!rpages)
	223	return 0;
	224	backend_pages = shmp(handle, rpages->shmp);
	225	if (!backend_pages)
	226	return 0;
	227	records_unread += v_read(config, &backend_pages->records_unread);
852c2936 MD	228	}
	229	return records_unread;
	230	}
	231
e92f3e28	232	#endif /* _LTTNG_RING_BUFFER_BACKEND_H */