1 #ifndef _LTTNG_RING_BUFFER_BACKEND_H
2 #define _LTTNG_RING_BUFFER_BACKEND_H
5 * libringbuffer/backend.h
7 * Ring buffer backend (API).
9 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
11 * This library is free software; you can redistribute it and/or
12 * modify it under the terms of the GNU Lesser General Public
13 * License as published by the Free Software Foundation; only
14 * version 2.1 of the License.
16 * This library is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
19 * Lesser General Public License for more details.
21 * You should have received a copy of the GNU Lesser General Public
22 * License along with this library; if not, write to the Free Software
23 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
25 * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
26 * the reader in flight recorder mode.
31 /* Internal helpers */
32 #include "backend_internal.h"
33 #include "frontend_internal.h"
35 /* Ring buffer backend API */
37 /* Ring buffer backend access (read/write) */
39 extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
40 size_t offset
, void *dest
, size_t len
,
41 struct lttng_ust_shm_handle
*handle
);
43 extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
44 size_t offset
, void *dest
, size_t len
,
45 struct lttng_ust_shm_handle
*handle
);
48 * Return the address where a given offset is located.
49 * Should be used to get the current subbuffer header pointer. Given we know
50 * it's never on a page boundary, it's safe to write directly to this address,
51 * as long as the write is never bigger than a page size.
54 lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
56 struct lttng_ust_shm_handle
*handle
);
58 lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend
*bufb
,
60 struct lttng_ust_shm_handle
*handle
);
63 * lib_ring_buffer_write - write data to a buffer backend
64 * @config : ring buffer instance configuration
65 * @ctx: ring buffer context. (input arguments only)
66 * @src : source pointer to copy from
67 * @len : length of data to copy
69 * This function copies "len" bytes of data from a source pointer to a buffer
70 * backend, at the current context offset. This is more or less a buffer
71 * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
72 * if copy is crossing a page boundary.
75 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config
*config
,
76 struct lttng_ust_lib_ring_buffer_ctx
*ctx
,
77 const void *src
, size_t len
)
79 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &ctx
->buf
->backend
;
80 struct channel_backend
*chanb
= &ctx
->chan
->backend
;
81 struct lttng_ust_shm_handle
*handle
= ctx
->handle
;
83 size_t offset
= ctx
->buf_offset
;
84 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*rpages
;
85 unsigned long sb_bindex
, id
;
87 offset
&= chanb
->buf_size
- 1;
88 sbidx
= offset
>> chanb
->subbuf_size_order
;
89 id
= shmp_index(handle
, bufb
->buf_wsb
, sbidx
)->id
;
90 sb_bindex
= subbuffer_id_get_index(config
, id
);
91 rpages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
92 CHAN_WARN_ON(ctx
->chan
,
93 config
->mode
== RING_BUFFER_OVERWRITE
94 && subbuffer_id_is_noref(config
, id
));
96 * Underlying layer should never ask for writes across
99 CHAN_WARN_ON(chanb
, offset
>= chanb
->buf_size
);
100 lib_ring_buffer_do_copy(config
,
101 shmp_index(handle
, shmp(handle
, rpages
->shmp
)->p
, offset
& (chanb
->subbuf_size
- 1)),
103 ctx
->buf_offset
+= len
;
107 * This accessor counts the number of unread records in a buffer.
108 * It only provides a consistent value if no reads not writes are performed
112 unsigned long lib_ring_buffer_get_records_unread(
113 const struct lttng_ust_lib_ring_buffer_config
*config
,
114 struct lttng_ust_lib_ring_buffer
*buf
,
115 struct lttng_ust_shm_handle
*handle
)
117 struct lttng_ust_lib_ring_buffer_backend
*bufb
= &buf
->backend
;
118 struct lttng_ust_lib_ring_buffer_backend_pages_shmp
*pages
;
119 unsigned long records_unread
= 0, sb_bindex
, id
;
122 for (i
= 0; i
< shmp(handle
, bufb
->chan
)->backend
.num_subbuf
; i
++) {
123 id
= shmp_index(handle
, bufb
->buf_wsb
, i
)->id
;
124 sb_bindex
= subbuffer_id_get_index(config
, id
);
125 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
126 records_unread
+= v_read(config
, &shmp(handle
, pages
->shmp
)->records_unread
);
128 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
129 id
= bufb
->buf_rsb
.id
;
130 sb_bindex
= subbuffer_id_get_index(config
, id
);
131 pages
= shmp_index(handle
, bufb
->array
, sb_bindex
);
132 records_unread
+= v_read(config
, &shmp(handle
, pages
->shmp
)->records_unread
);
134 return records_unread
;
137 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */