1 #ifndef _LIB_RING_BUFFER_BACKEND_INTERNAL_H
2 #define _LIB_RING_BUFFER_BACKEND_INTERNAL_H
5 * lib/ringbuffer/backend_internal.h
7 * Ring buffer backend (internal helpers).
9 * Copyright (C) 2008-2012 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
26 #include "../../wrapper/ringbuffer/config.h"
27 #include "../../wrapper/ringbuffer/backend_types.h"
28 #include "../../wrapper/ringbuffer/frontend_types.h"
29 #include <linux/string.h>
30 #include <linux/uaccess.h>
32 /* Ring buffer backend API presented to the frontend */
34 /* Ring buffer and channel backend create/free */
36 int lib_ring_buffer_backend_create(struct lib_ring_buffer_backend
*bufb
,
37 struct channel_backend
*chan
, int cpu
);
38 void channel_backend_unregister_notifiers(struct channel_backend
*chanb
);
39 void lib_ring_buffer_backend_free(struct lib_ring_buffer_backend
*bufb
);
40 int channel_backend_init(struct channel_backend
*chanb
,
42 const struct lib_ring_buffer_config
*config
,
43 void *priv
, size_t subbuf_size
,
45 void channel_backend_free(struct channel_backend
*chanb
);
47 void lib_ring_buffer_backend_reset(struct lib_ring_buffer_backend
*bufb
);
48 void channel_backend_reset(struct channel_backend
*chanb
);
50 int lib_ring_buffer_backend_init(void);
51 void lib_ring_buffer_backend_exit(void);
53 extern void _lib_ring_buffer_write(struct lib_ring_buffer_backend
*bufb
,
54 size_t offset
, const void *src
, size_t len
,
56 extern void _lib_ring_buffer_memset(struct lib_ring_buffer_backend
*bufb
,
57 size_t offset
, int c
, size_t len
,
59 extern void _lib_ring_buffer_copy_from_user_inatomic(struct lib_ring_buffer_backend
*bufb
,
60 size_t offset
, const void *src
,
61 size_t len
, ssize_t pagecpy
);
64 * Subbuffer ID bits for overwrite mode. Need to fit within a single word to be
65 * exchanged atomically.
67 * Top half word, except lowest bit, belongs to "offset", which is used to keep
68 * to count the produced buffers. For overwrite mode, this provides the
69 * consumer with the capacity to read subbuffers in order, handling the
70 * situation where producers would write up to 2^15 buffers (or 2^31 for 64-bit
71 * systems) concurrently with a single execution of get_subbuf (between offset
72 * sampling and subbuffer ID exchange).
75 #define HALF_ULONG_BITS (BITS_PER_LONG >> 1)
77 #define SB_ID_OFFSET_SHIFT (HALF_ULONG_BITS + 1)
78 #define SB_ID_OFFSET_COUNT (1UL << SB_ID_OFFSET_SHIFT)
79 #define SB_ID_OFFSET_MASK (~(SB_ID_OFFSET_COUNT - 1))
81 * Lowest bit of top word half belongs to noref. Used only for overwrite mode.
83 #define SB_ID_NOREF_SHIFT (SB_ID_OFFSET_SHIFT - 1)
84 #define SB_ID_NOREF_COUNT (1UL << SB_ID_NOREF_SHIFT)
85 #define SB_ID_NOREF_MASK SB_ID_NOREF_COUNT
87 * In overwrite mode: lowest half of word is used for index.
88 * Limit of 2^16 subbuffers per buffer on 32-bit, 2^32 on 64-bit.
89 * In producer-consumer mode: whole word used for index.
91 #define SB_ID_INDEX_SHIFT 0
92 #define SB_ID_INDEX_COUNT (1UL << SB_ID_INDEX_SHIFT)
93 #define SB_ID_INDEX_MASK (SB_ID_NOREF_COUNT - 1)
96 * Construct the subbuffer id from offset, index and noref. Use only the index
97 * for producer-consumer mode (offset and noref are only used in overwrite
101 unsigned long subbuffer_id(const struct lib_ring_buffer_config
*config
,
102 unsigned long offset
, unsigned long noref
,
105 if (config
->mode
== RING_BUFFER_OVERWRITE
)
106 return (offset
<< SB_ID_OFFSET_SHIFT
)
107 | (noref
<< SB_ID_NOREF_SHIFT
)
114 * Compare offset with the offset contained within id. Return 1 if the offset
115 * bits are identical, else 0.
118 int subbuffer_id_compare_offset(const struct lib_ring_buffer_config
*config
,
119 unsigned long id
, unsigned long offset
)
121 return (id
& SB_ID_OFFSET_MASK
) == (offset
<< SB_ID_OFFSET_SHIFT
);
125 unsigned long subbuffer_id_get_index(const struct lib_ring_buffer_config
*config
,
128 if (config
->mode
== RING_BUFFER_OVERWRITE
)
129 return id
& SB_ID_INDEX_MASK
;
135 unsigned long subbuffer_id_is_noref(const struct lib_ring_buffer_config
*config
,
138 if (config
->mode
== RING_BUFFER_OVERWRITE
)
139 return !!(id
& SB_ID_NOREF_MASK
);
145 * Only used by reader on subbuffer ID it has exclusive access to. No volatile
149 void subbuffer_id_set_noref(const struct lib_ring_buffer_config
*config
,
152 if (config
->mode
== RING_BUFFER_OVERWRITE
)
153 *id
|= SB_ID_NOREF_MASK
;
157 void subbuffer_id_set_noref_offset(const struct lib_ring_buffer_config
*config
,
158 unsigned long *id
, unsigned long offset
)
162 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
164 tmp
&= ~SB_ID_OFFSET_MASK
;
165 tmp
|= offset
<< SB_ID_OFFSET_SHIFT
;
166 tmp
|= SB_ID_NOREF_MASK
;
167 /* Volatile store, read concurrently by readers. */
168 ACCESS_ONCE(*id
) = tmp
;
172 /* No volatile access, since already used locally */
174 void subbuffer_id_clear_noref(const struct lib_ring_buffer_config
*config
,
177 if (config
->mode
== RING_BUFFER_OVERWRITE
)
178 *id
&= ~SB_ID_NOREF_MASK
;
182 * For overwrite mode, cap the number of subbuffers per buffer to:
183 * 2^16 on 32-bit architectures
184 * 2^32 on 64-bit architectures
185 * This is required to fit in the index part of the ID. Return 0 on success,
189 int subbuffer_id_check_index(const struct lib_ring_buffer_config
*config
,
190 unsigned long num_subbuf
)
192 if (config
->mode
== RING_BUFFER_OVERWRITE
)
193 return (num_subbuf
> (1UL << HALF_ULONG_BITS
)) ? -EPERM
: 0;
199 void subbuffer_count_record(const struct lib_ring_buffer_config
*config
,
200 struct lib_ring_buffer_backend
*bufb
,
203 unsigned long sb_bindex
;
205 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
206 v_inc(config
, &bufb
->array
[sb_bindex
]->records_commit
);
210 * Reader has exclusive subbuffer access for record consumption. No need to
211 * perform the decrement atomically.
214 void subbuffer_consume_record(const struct lib_ring_buffer_config
*config
,
215 struct lib_ring_buffer_backend
*bufb
)
217 unsigned long sb_bindex
;
219 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
220 CHAN_WARN_ON(bufb
->chan
,
221 !v_read(config
, &bufb
->array
[sb_bindex
]->records_unread
));
222 /* Non-atomic decrement protected by exclusive subbuffer access */
223 _v_dec(config
, &bufb
->array
[sb_bindex
]->records_unread
);
224 v_inc(config
, &bufb
->records_read
);
228 unsigned long subbuffer_get_records_count(
229 const struct lib_ring_buffer_config
*config
,
230 struct lib_ring_buffer_backend
*bufb
,
233 unsigned long sb_bindex
;
235 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
236 return v_read(config
, &bufb
->array
[sb_bindex
]->records_commit
);
240 * Must be executed at subbuffer delivery when the writer has _exclusive_
241 * subbuffer access. See lib_ring_buffer_check_deliver() for details.
242 * lib_ring_buffer_get_records_count() must be called to get the records
243 * count before this function, because it resets the records_commit
247 unsigned long subbuffer_count_records_overrun(
248 const struct lib_ring_buffer_config
*config
,
249 struct lib_ring_buffer_backend
*bufb
,
252 struct lib_ring_buffer_backend_pages
*pages
;
253 unsigned long overruns
, sb_bindex
;
255 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
256 pages
= bufb
->array
[sb_bindex
];
257 overruns
= v_read(config
, &pages
->records_unread
);
258 v_set(config
, &pages
->records_unread
,
259 v_read(config
, &pages
->records_commit
));
260 v_set(config
, &pages
->records_commit
, 0);
266 void subbuffer_set_data_size(const struct lib_ring_buffer_config
*config
,
267 struct lib_ring_buffer_backend
*bufb
,
269 unsigned long data_size
)
271 struct lib_ring_buffer_backend_pages
*pages
;
272 unsigned long sb_bindex
;
274 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
275 pages
= bufb
->array
[sb_bindex
];
276 pages
->data_size
= data_size
;
280 unsigned long subbuffer_get_read_data_size(
281 const struct lib_ring_buffer_config
*config
,
282 struct lib_ring_buffer_backend
*bufb
)
284 struct lib_ring_buffer_backend_pages
*pages
;
285 unsigned long sb_bindex
;
287 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_rsb
.id
);
288 pages
= bufb
->array
[sb_bindex
];
289 return pages
->data_size
;
293 unsigned long subbuffer_get_data_size(
294 const struct lib_ring_buffer_config
*config
,
295 struct lib_ring_buffer_backend
*bufb
,
298 struct lib_ring_buffer_backend_pages
*pages
;
299 unsigned long sb_bindex
;
301 sb_bindex
= subbuffer_id_get_index(config
, bufb
->buf_wsb
[idx
].id
);
302 pages
= bufb
->array
[sb_bindex
];
303 return pages
->data_size
;
307 * lib_ring_buffer_clear_noref - Clear the noref subbuffer flag, called by
311 void lib_ring_buffer_clear_noref(const struct lib_ring_buffer_config
*config
,
312 struct lib_ring_buffer_backend
*bufb
,
315 unsigned long id
, new_id
;
317 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
321 * Performing a volatile access to read the sb_pages, because we want to
322 * read a coherent version of the pointer and the associated noref flag.
324 id
= ACCESS_ONCE(bufb
->buf_wsb
[idx
].id
);
326 /* This check is called on the fast path for each record. */
327 if (likely(!subbuffer_id_is_noref(config
, id
))) {
329 * Store after load dependency ordering the writes to
330 * the subbuffer after load and test of the noref flag
331 * matches the memory barrier implied by the cmpxchg()
332 * in update_read_sb_index().
334 return; /* Already writing to this buffer */
337 subbuffer_id_clear_noref(config
, &new_id
);
338 new_id
= cmpxchg(&bufb
->buf_wsb
[idx
].id
, id
, new_id
);
339 if (likely(new_id
== id
))
346 * lib_ring_buffer_set_noref_offset - Set the noref subbuffer flag and offset,
350 void lib_ring_buffer_set_noref_offset(const struct lib_ring_buffer_config
*config
,
351 struct lib_ring_buffer_backend
*bufb
,
352 unsigned long idx
, unsigned long offset
)
354 if (config
->mode
!= RING_BUFFER_OVERWRITE
)
358 * Because ring_buffer_set_noref() is only called by a single thread
359 * (the one which updated the cc_sb value), there are no concurrent
360 * updates to take care of: other writers have not updated cc_sb, so
361 * they cannot set the noref flag, and concurrent readers cannot modify
362 * the pointer because the noref flag is not set yet.
363 * The smp_wmb() in ring_buffer_commit() takes care of ordering writes
364 * to the subbuffer before this set noref operation.
365 * subbuffer_set_noref() uses a volatile store to deal with concurrent
366 * readers of the noref flag.
368 CHAN_WARN_ON(bufb
->chan
,
369 subbuffer_id_is_noref(config
, bufb
->buf_wsb
[idx
].id
));
371 * Memory barrier that ensures counter stores are ordered before set
375 subbuffer_id_set_noref_offset(config
, &bufb
->buf_wsb
[idx
].id
, offset
);
379 * update_read_sb_index - Read-side subbuffer index update.
382 int update_read_sb_index(const struct lib_ring_buffer_config
*config
,
383 struct lib_ring_buffer_backend
*bufb
,
384 struct channel_backend
*chanb
,
385 unsigned long consumed_idx
,
386 unsigned long consumed_count
)
388 unsigned long old_id
, new_id
;
390 if (config
->mode
== RING_BUFFER_OVERWRITE
) {
392 * Exchange the target writer subbuffer with our own unused
393 * subbuffer. No need to use ACCESS_ONCE() here to read the
394 * old_wpage, because the value read will be confirmed by the
395 * following cmpxchg().
397 old_id
= bufb
->buf_wsb
[consumed_idx
].id
;
398 if (unlikely(!subbuffer_id_is_noref(config
, old_id
)))
401 * Make sure the offset count we are expecting matches the one
402 * indicated by the writer.
404 if (unlikely(!subbuffer_id_compare_offset(config
, old_id
,
407 CHAN_WARN_ON(bufb
->chan
,
408 !subbuffer_id_is_noref(config
, bufb
->buf_rsb
.id
));
409 subbuffer_id_set_noref_offset(config
, &bufb
->buf_rsb
.id
,
411 new_id
= cmpxchg(&bufb
->buf_wsb
[consumed_idx
].id
, old_id
,
413 if (unlikely(old_id
!= new_id
))
415 bufb
->buf_rsb
.id
= new_id
;
417 /* No page exchange, use the writer page directly */
418 bufb
->buf_rsb
.id
= bufb
->buf_wsb
[consumed_idx
].id
;
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.
428 #define lib_ring_buffer_do_copy(config, dest, src, len) \
430 size_t __len = (len); \
431 if (__builtin_constant_p(len)) \
432 memcpy(dest, src, __len); \
434 inline_memcpy(dest, src, __len); \
438 * We use __copy_from_user_inatomic to copy userspace data since we already
439 * did the access_ok for the whole range.
442 unsigned long lib_ring_buffer_do_copy_from_user_inatomic(void *dest
,
443 const void __user
*src
,
446 return __copy_from_user_inatomic(dest
, src
, len
);
450 * write len bytes to dest with c
453 void lib_ring_buffer_do_memset(char *dest
, int c
,
458 for (i
= 0; i
< len
; i
++)
462 #endif /* _LIB_RING_BUFFER_BACKEND_INTERNAL_H */