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b6cf8b3f JO |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | #include <linux/kernel.h> | |
4 | #include <linux/irqflags.h> | |
5 | #include <linux/string.h> | |
6 | #include <linux/errno.h> | |
7 | #include <linux/bug.h> | |
8 | #include "printk_ringbuffer.h" | |
9 | ||
10 | /** | |
11 | * DOC: printk_ringbuffer overview | |
12 | * | |
13 | * Data Structure | |
14 | * -------------- | |
15 | * The printk_ringbuffer is made up of 3 internal ringbuffers: | |
16 | * | |
17 | * desc_ring | |
cfe2790b JO |
18 | * A ring of descriptors and their meta data (such as sequence number, |
19 | * timestamp, loglevel, etc.) as well as internal state information about | |
20 | * the record and logical positions specifying where in the other | |
f35efc78 | 21 | * ringbuffer the text strings are located. |
b6cf8b3f JO |
22 | * |
23 | * text_data_ring | |
24 | * A ring of data blocks. A data block consists of an unsigned long | |
25 | * integer (ID) that maps to a desc_ring index followed by the text | |
26 | * string of the record. | |
27 | * | |
b6cf8b3f JO |
28 | * The internal state information of a descriptor is the key element to allow |
29 | * readers and writers to locklessly synchronize access to the data. | |
30 | * | |
31 | * Implementation | |
32 | * -------------- | |
33 | * | |
34 | * Descriptor Ring | |
35 | * ~~~~~~~~~~~~~~~ | |
cfe2790b JO |
36 | * The descriptor ring is an array of descriptors. A descriptor contains |
37 | * essential meta data to track the data of a printk record using | |
f35efc78 JO |
38 | * blk_lpos structs pointing to associated text data blocks (see |
39 | * "Data Rings" below). Each descriptor is assigned an ID that maps | |
cfe2790b JO |
40 | * directly to index values of the descriptor array and has a state. The ID |
41 | * and the state are bitwise combined into a single descriptor field named | |
42 | * @state_var, allowing ID and state to be synchronously and atomically | |
43 | * updated. | |
b6cf8b3f | 44 | * |
4cfc7258 | 45 | * Descriptors have four states: |
b6cf8b3f JO |
46 | * |
47 | * reserved | |
48 | * A writer is modifying the record. | |
49 | * | |
50 | * committed | |
4cfc7258 JO |
51 | * The record and all its data are written. A writer can reopen the |
52 | * descriptor (transitioning it back to reserved), but in the committed | |
53 | * state the data is consistent. | |
54 | * | |
55 | * finalized | |
56 | * The record and all its data are complete and available for reading. A | |
57 | * writer cannot reopen the descriptor. | |
b6cf8b3f JO |
58 | * |
59 | * reusable | |
f35efc78 JO |
60 | * The record exists, but its text and/or meta data may no longer be |
61 | * available. | |
b6cf8b3f JO |
62 | * |
63 | * Querying the @state_var of a record requires providing the ID of the | |
4cfc7258 | 64 | * descriptor to query. This can yield a possible fifth (pseudo) state: |
b6cf8b3f JO |
65 | * |
66 | * miss | |
67 | * The descriptor being queried has an unexpected ID. | |
68 | * | |
69 | * The descriptor ring has a @tail_id that contains the ID of the oldest | |
70 | * descriptor and @head_id that contains the ID of the newest descriptor. | |
71 | * | |
72 | * When a new descriptor should be created (and the ring is full), the tail | |
73 | * descriptor is invalidated by first transitioning to the reusable state and | |
74 | * then invalidating all tail data blocks up to and including the data blocks | |
f35efc78 | 75 | * associated with the tail descriptor (for the text ring). Then |
b6cf8b3f JO |
76 | * @tail_id is advanced, followed by advancing @head_id. And finally the |
77 | * @state_var of the new descriptor is initialized to the new ID and reserved | |
78 | * state. | |
79 | * | |
80 | * The @tail_id can only be advanced if the new @tail_id would be in the | |
81 | * committed or reusable queried state. This makes it possible that a valid | |
82 | * sequence number of the tail is always available. | |
83 | * | |
4cfc7258 JO |
84 | * Descriptor Finalization |
85 | * ~~~~~~~~~~~~~~~~~~~~~~~ | |
86 | * When a writer calls the commit function prb_commit(), record data is | |
87 | * fully stored and is consistent within the ringbuffer. However, a writer can | |
88 | * reopen that record, claiming exclusive access (as with prb_reserve()), and | |
89 | * modify that record. When finished, the writer must again commit the record. | |
90 | * | |
91 | * In order for a record to be made available to readers (and also become | |
92 | * recyclable for writers), it must be finalized. A finalized record cannot be | |
93 | * reopened and can never become "unfinalized". Record finalization can occur | |
94 | * in three different scenarios: | |
95 | * | |
96 | * 1) A writer can simultaneously commit and finalize its record by calling | |
97 | * prb_final_commit() instead of prb_commit(). | |
98 | * | |
99 | * 2) When a new record is reserved and the previous record has been | |
100 | * committed via prb_commit(), that previous record is automatically | |
101 | * finalized. | |
102 | * | |
103 | * 3) When a record is committed via prb_commit() and a newer record | |
104 | * already exists, the record being committed is automatically finalized. | |
105 | * | |
f35efc78 JO |
106 | * Data Ring |
107 | * ~~~~~~~~~ | |
108 | * The text data ring is a byte array composed of data blocks. Data blocks are | |
b6cf8b3f JO |
109 | * referenced by blk_lpos structs that point to the logical position of the |
110 | * beginning of a data block and the beginning of the next adjacent data | |
111 | * block. Logical positions are mapped directly to index values of the byte | |
112 | * array ringbuffer. | |
113 | * | |
114 | * Each data block consists of an ID followed by the writer data. The ID is | |
115 | * the identifier of a descriptor that is associated with the data block. A | |
116 | * given data block is considered valid if all of the following conditions | |
117 | * are met: | |
118 | * | |
119 | * 1) The descriptor associated with the data block is in the committed | |
4cfc7258 | 120 | * or finalized queried state. |
b6cf8b3f JO |
121 | * |
122 | * 2) The blk_lpos struct within the descriptor associated with the data | |
123 | * block references back to the same data block. | |
124 | * | |
125 | * 3) The data block is within the head/tail logical position range. | |
126 | * | |
127 | * If the writer data of a data block would extend beyond the end of the | |
128 | * byte array, only the ID of the data block is stored at the logical | |
129 | * position and the full data block (ID and writer data) is stored at the | |
130 | * beginning of the byte array. The referencing blk_lpos will point to the | |
131 | * ID before the wrap and the next data block will be at the logical | |
132 | * position adjacent the full data block after the wrap. | |
133 | * | |
134 | * Data rings have a @tail_lpos that points to the beginning of the oldest | |
135 | * data block and a @head_lpos that points to the logical position of the | |
136 | * next (not yet existing) data block. | |
137 | * | |
138 | * When a new data block should be created (and the ring is full), tail data | |
139 | * blocks will first be invalidated by putting their associated descriptors | |
140 | * into the reusable state and then pushing the @tail_lpos forward beyond | |
141 | * them. Then the @head_lpos is pushed forward and is associated with a new | |
142 | * descriptor. If a data block is not valid, the @tail_lpos cannot be | |
143 | * advanced beyond it. | |
144 | * | |
cfe2790b JO |
145 | * Info Array |
146 | * ~~~~~~~~~~ | |
147 | * The general meta data of printk records are stored in printk_info structs, | |
148 | * stored in an array with the same number of elements as the descriptor ring. | |
149 | * Each info corresponds to the descriptor of the same index in the | |
150 | * descriptor ring. Info validity is confirmed by evaluating the corresponding | |
151 | * descriptor before and after loading the info. | |
152 | * | |
b6cf8b3f JO |
153 | * Usage |
154 | * ----- | |
155 | * Here are some simple examples demonstrating writers and readers. For the | |
156 | * examples a global ringbuffer (test_rb) is available (which is not the | |
157 | * actual ringbuffer used by printk):: | |
158 | * | |
f35efc78 | 159 | * DEFINE_PRINTKRB(test_rb, 15, 5); |
b6cf8b3f JO |
160 | * |
161 | * This ringbuffer allows up to 32768 records (2 ^ 15) and has a size of | |
f35efc78 | 162 | * 1 MiB (2 ^ (15 + 5)) for text data. |
b6cf8b3f JO |
163 | * |
164 | * Sample writer code:: | |
165 | * | |
b6cf8b3f JO |
166 | * const char *textstr = "message text"; |
167 | * struct prb_reserved_entry e; | |
168 | * struct printk_record r; | |
169 | * | |
170 | * // specify how much to allocate | |
f35efc78 | 171 | * prb_rec_init_wr(&r, strlen(textstr) + 1); |
b6cf8b3f JO |
172 | * |
173 | * if (prb_reserve(&e, &test_rb, &r)) { | |
174 | * snprintf(r.text_buf, r.text_buf_size, "%s", textstr); | |
b6cf8b3f | 175 | * |
f35efc78 | 176 | * r.info->text_len = strlen(textstr); |
b6cf8b3f | 177 | * r.info->ts_nsec = local_clock(); |
f35efc78 | 178 | * r.info->caller_id = printk_caller_id(); |
b6cf8b3f | 179 | * |
f35efc78 | 180 | * // commit and finalize the record |
4cfc7258 JO |
181 | * prb_final_commit(&e); |
182 | * } | |
183 | * | |
184 | * Note that additional writer functions are available to extend a record | |
185 | * after it has been committed but not yet finalized. This can be done as | |
186 | * long as no new records have been reserved and the caller is the same. | |
187 | * | |
188 | * Sample writer code (record extending):: | |
189 | * | |
190 | * // alternate rest of previous example | |
f35efc78 | 191 | * |
4cfc7258 | 192 | * r.info->text_len = strlen(textstr); |
f35efc78 | 193 | * r.info->ts_nsec = local_clock(); |
4cfc7258 JO |
194 | * r.info->caller_id = printk_caller_id(); |
195 | * | |
196 | * // commit the record (but do not finalize yet) | |
b6cf8b3f JO |
197 | * prb_commit(&e); |
198 | * } | |
199 | * | |
4cfc7258 JO |
200 | * ... |
201 | * | |
202 | * // specify additional 5 bytes text space to extend | |
f35efc78 | 203 | * prb_rec_init_wr(&r, 5); |
4cfc7258 | 204 | * |
59f8bcca JO |
205 | * // try to extend, but only if it does not exceed 32 bytes |
206 | * if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id()), 32) { | |
4cfc7258 JO |
207 | * snprintf(&r.text_buf[r.info->text_len], |
208 | * r.text_buf_size - r.info->text_len, "hello"); | |
209 | * | |
210 | * r.info->text_len += 5; | |
211 | * | |
f35efc78 | 212 | * // commit and finalize the record |
4cfc7258 JO |
213 | * prb_final_commit(&e); |
214 | * } | |
215 | * | |
b6cf8b3f JO |
216 | * Sample reader code:: |
217 | * | |
218 | * struct printk_info info; | |
219 | * struct printk_record r; | |
220 | * char text_buf[32]; | |
b6cf8b3f JO |
221 | * u64 seq; |
222 | * | |
f35efc78 | 223 | * prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf)); |
b6cf8b3f JO |
224 | * |
225 | * prb_for_each_record(0, &test_rb, &seq, &r) { | |
226 | * if (info.seq != seq) | |
227 | * pr_warn("lost %llu records\n", info.seq - seq); | |
228 | * | |
229 | * if (info.text_len > r.text_buf_size) { | |
230 | * pr_warn("record %llu text truncated\n", info.seq); | |
231 | * text_buf[r.text_buf_size - 1] = 0; | |
232 | * } | |
233 | * | |
f35efc78 JO |
234 | * pr_info("%llu: %llu: %s\n", info.seq, info.ts_nsec, |
235 | * &text_buf[0]); | |
b6cf8b3f JO |
236 | * } |
237 | * | |
238 | * Note that additional less convenient reader functions are available to | |
239 | * allow complex record access. | |
240 | * | |
241 | * ABA Issues | |
242 | * ~~~~~~~~~~ | |
243 | * To help avoid ABA issues, descriptors are referenced by IDs (array index | |
244 | * values combined with tagged bits counting array wraps) and data blocks are | |
245 | * referenced by logical positions (array index values combined with tagged | |
246 | * bits counting array wraps). However, on 32-bit systems the number of | |
247 | * tagged bits is relatively small such that an ABA incident is (at least | |
248 | * theoretically) possible. For example, if 4 million maximally sized (1KiB) | |
249 | * printk messages were to occur in NMI context on a 32-bit system, the | |
250 | * interrupted context would not be able to recognize that the 32-bit integer | |
251 | * completely wrapped and thus represents a different data block than the one | |
252 | * the interrupted context expects. | |
253 | * | |
254 | * To help combat this possibility, additional state checking is performed | |
255 | * (such as using cmpxchg() even though set() would suffice). These extra | |
256 | * checks are commented as such and will hopefully catch any ABA issue that | |
257 | * a 32-bit system might experience. | |
258 | * | |
259 | * Memory Barriers | |
260 | * ~~~~~~~~~~~~~~~ | |
261 | * Multiple memory barriers are used. To simplify proving correctness and | |
262 | * generating litmus tests, lines of code related to memory barriers | |
263 | * (loads, stores, and the associated memory barriers) are labeled:: | |
264 | * | |
265 | * LMM(function:letter) | |
266 | * | |
267 | * Comments reference the labels using only the "function:letter" part. | |
268 | * | |
269 | * The memory barrier pairs and their ordering are: | |
270 | * | |
271 | * desc_reserve:D / desc_reserve:B | |
272 | * push descriptor tail (id), then push descriptor head (id) | |
273 | * | |
274 | * desc_reserve:D / data_push_tail:B | |
275 | * push data tail (lpos), then set new descriptor reserved (state) | |
276 | * | |
277 | * desc_reserve:D / desc_push_tail:C | |
278 | * push descriptor tail (id), then set new descriptor reserved (state) | |
279 | * | |
280 | * desc_reserve:D / prb_first_seq:C | |
281 | * push descriptor tail (id), then set new descriptor reserved (state) | |
282 | * | |
283 | * desc_reserve:F / desc_read:D | |
284 | * set new descriptor id and reserved (state), then allow writer changes | |
285 | * | |
4cfc7258 | 286 | * data_alloc:A (or data_realloc:A) / desc_read:D |
b6cf8b3f JO |
287 | * set old descriptor reusable (state), then modify new data block area |
288 | * | |
4cfc7258 | 289 | * data_alloc:A (or data_realloc:A) / data_push_tail:B |
b6cf8b3f JO |
290 | * push data tail (lpos), then modify new data block area |
291 | * | |
4cfc7258 | 292 | * _prb_commit:B / desc_read:B |
b6cf8b3f JO |
293 | * store writer changes, then set new descriptor committed (state) |
294 | * | |
4cfc7258 JO |
295 | * desc_reopen_last:A / _prb_commit:B |
296 | * set descriptor reserved (state), then read descriptor data | |
297 | * | |
298 | * _prb_commit:B / desc_reserve:D | |
299 | * set new descriptor committed (state), then check descriptor head (id) | |
300 | * | |
b6cf8b3f JO |
301 | * data_push_tail:D / data_push_tail:A |
302 | * set descriptor reusable (state), then push data tail (lpos) | |
303 | * | |
304 | * desc_push_tail:B / desc_reserve:D | |
305 | * set descriptor reusable (state), then push descriptor tail (id) | |
306 | */ | |
307 | ||
308 | #define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits) | |
309 | #define DATA_SIZE_MASK(data_ring) (DATA_SIZE(data_ring) - 1) | |
310 | ||
311 | #define DESCS_COUNT(desc_ring) _DESCS_COUNT((desc_ring)->count_bits) | |
312 | #define DESCS_COUNT_MASK(desc_ring) (DESCS_COUNT(desc_ring) - 1) | |
313 | ||
314 | /* Determine the data array index from a logical position. */ | |
315 | #define DATA_INDEX(data_ring, lpos) ((lpos) & DATA_SIZE_MASK(data_ring)) | |
316 | ||
317 | /* Determine the desc array index from an ID or sequence number. */ | |
318 | #define DESC_INDEX(desc_ring, n) ((n) & DESCS_COUNT_MASK(desc_ring)) | |
319 | ||
320 | /* Determine how many times the data array has wrapped. */ | |
321 | #define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits) | |
322 | ||
d397820f JO |
323 | /* Determine if a logical position refers to a data-less block. */ |
324 | #define LPOS_DATALESS(lpos) ((lpos) & 1UL) | |
e3bc0401 JO |
325 | #define BLK_DATALESS(blk) (LPOS_DATALESS((blk)->begin) && \ |
326 | LPOS_DATALESS((blk)->next)) | |
d397820f | 327 | |
b6cf8b3f JO |
328 | /* Get the logical position at index 0 of the current wrap. */ |
329 | #define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \ | |
330 | ((lpos) & ~DATA_SIZE_MASK(data_ring)) | |
331 | ||
332 | /* Get the ID for the same index of the previous wrap as the given ID. */ | |
333 | #define DESC_ID_PREV_WRAP(desc_ring, id) \ | |
334 | DESC_ID((id) - DESCS_COUNT(desc_ring)) | |
335 | ||
336 | /* | |
337 | * A data block: mapped directly to the beginning of the data block area | |
338 | * specified as a logical position within the data ring. | |
339 | * | |
340 | * @id: the ID of the associated descriptor | |
341 | * @data: the writer data | |
342 | * | |
343 | * Note that the size of a data block is only known by its associated | |
344 | * descriptor. | |
345 | */ | |
346 | struct prb_data_block { | |
347 | unsigned long id; | |
a38283da | 348 | char data[]; |
b6cf8b3f JO |
349 | }; |
350 | ||
351 | /* | |
352 | * Return the descriptor associated with @n. @n can be either a | |
353 | * descriptor ID or a sequence number. | |
354 | */ | |
355 | static struct prb_desc *to_desc(struct prb_desc_ring *desc_ring, u64 n) | |
356 | { | |
357 | return &desc_ring->descs[DESC_INDEX(desc_ring, n)]; | |
358 | } | |
359 | ||
cfe2790b JO |
360 | /* |
361 | * Return the printk_info associated with @n. @n can be either a | |
362 | * descriptor ID or a sequence number. | |
363 | */ | |
364 | static struct printk_info *to_info(struct prb_desc_ring *desc_ring, u64 n) | |
365 | { | |
366 | return &desc_ring->infos[DESC_INDEX(desc_ring, n)]; | |
367 | } | |
368 | ||
b6cf8b3f JO |
369 | static struct prb_data_block *to_block(struct prb_data_ring *data_ring, |
370 | unsigned long begin_lpos) | |
371 | { | |
372 | return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)]; | |
373 | } | |
374 | ||
375 | /* | |
376 | * Increase the data size to account for data block meta data plus any | |
377 | * padding so that the adjacent data block is aligned on the ID size. | |
378 | */ | |
379 | static unsigned int to_blk_size(unsigned int size) | |
380 | { | |
381 | struct prb_data_block *db = NULL; | |
382 | ||
383 | size += sizeof(*db); | |
384 | size = ALIGN(size, sizeof(db->id)); | |
385 | return size; | |
386 | } | |
387 | ||
388 | /* | |
389 | * Sanity checker for reserve size. The ringbuffer code assumes that a data | |
390 | * block does not exceed the maximum possible size that could fit within the | |
391 | * ringbuffer. This function provides that basic size check so that the | |
392 | * assumption is safe. | |
b6cf8b3f JO |
393 | */ |
394 | static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size) | |
395 | { | |
396 | struct prb_data_block *db = NULL; | |
397 | ||
b6cf8b3f | 398 | if (size == 0) |
d397820f | 399 | return true; |
b6cf8b3f JO |
400 | |
401 | /* | |
402 | * Ensure the alignment padded size could possibly fit in the data | |
403 | * array. The largest possible data block must still leave room for | |
404 | * at least the ID of the next block. | |
405 | */ | |
406 | size = to_blk_size(size); | |
407 | if (size > DATA_SIZE(data_ring) - sizeof(db->id)) | |
408 | return false; | |
409 | ||
410 | return true; | |
411 | } | |
412 | ||
b6cf8b3f JO |
413 | /* Query the state of a descriptor. */ |
414 | static enum desc_state get_desc_state(unsigned long id, | |
415 | unsigned long state_val) | |
416 | { | |
417 | if (id != DESC_ID(state_val)) | |
418 | return desc_miss; | |
419 | ||
10dcb06d | 420 | return DESC_STATE(state_val); |
b6cf8b3f JO |
421 | } |
422 | ||
423 | /* | |
ce003d67 JO |
424 | * Get a copy of a specified descriptor and return its queried state. If the |
425 | * descriptor is in an inconsistent state (miss or reserved), the caller can | |
426 | * only expect the descriptor's @state_var field to be valid. | |
cfe2790b JO |
427 | * |
428 | * The sequence number and caller_id can be optionally retrieved. Like all | |
429 | * non-state_var data, they are only valid if the descriptor is in a | |
430 | * consistent state. | |
b6cf8b3f JO |
431 | */ |
432 | static enum desc_state desc_read(struct prb_desc_ring *desc_ring, | |
cfe2790b JO |
433 | unsigned long id, struct prb_desc *desc_out, |
434 | u64 *seq_out, u32 *caller_id_out) | |
b6cf8b3f | 435 | { |
cfe2790b | 436 | struct printk_info *info = to_info(desc_ring, id); |
b6cf8b3f JO |
437 | struct prb_desc *desc = to_desc(desc_ring, id); |
438 | atomic_long_t *state_var = &desc->state_var; | |
439 | enum desc_state d_state; | |
440 | unsigned long state_val; | |
441 | ||
442 | /* Check the descriptor state. */ | |
443 | state_val = atomic_long_read(state_var); /* LMM(desc_read:A) */ | |
444 | d_state = get_desc_state(id, state_val); | |
ce003d67 JO |
445 | if (d_state == desc_miss || d_state == desc_reserved) { |
446 | /* | |
447 | * The descriptor is in an inconsistent state. Set at least | |
448 | * @state_var so that the caller can see the details of | |
449 | * the inconsistent state. | |
450 | */ | |
451 | goto out; | |
452 | } | |
b6cf8b3f JO |
453 | |
454 | /* | |
455 | * Guarantee the state is loaded before copying the descriptor | |
456 | * content. This avoids copying obsolete descriptor content that might | |
4cfc7258 | 457 | * not apply to the descriptor state. This pairs with _prb_commit:B. |
b6cf8b3f JO |
458 | * |
459 | * Memory barrier involvement: | |
460 | * | |
4cfc7258 JO |
461 | * If desc_read:A reads from _prb_commit:B, then desc_read:C reads |
462 | * from _prb_commit:A. | |
b6cf8b3f JO |
463 | * |
464 | * Relies on: | |
465 | * | |
4cfc7258 | 466 | * WMB from _prb_commit:A to _prb_commit:B |
b6cf8b3f JO |
467 | * matching |
468 | * RMB from desc_read:A to desc_read:C | |
469 | */ | |
470 | smp_rmb(); /* LMM(desc_read:B) */ | |
471 | ||
472 | /* | |
473 | * Copy the descriptor data. The data is not valid until the | |
e7c1fe21 JO |
474 | * state has been re-checked. A memcpy() for all of @desc |
475 | * cannot be used because of the atomic_t @state_var field. | |
b6cf8b3f | 476 | */ |
e7c1fe21 | 477 | memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos, |
cfe2790b | 478 | sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */ |
cfe2790b JO |
479 | if (seq_out) |
480 | *seq_out = info->seq; /* also part of desc_read:C */ | |
481 | if (caller_id_out) | |
482 | *caller_id_out = info->caller_id; /* also part of desc_read:C */ | |
b6cf8b3f JO |
483 | |
484 | /* | |
485 | * 1. Guarantee the descriptor content is loaded before re-checking | |
486 | * the state. This avoids reading an obsolete descriptor state | |
487 | * that may not apply to the copied content. This pairs with | |
488 | * desc_reserve:F. | |
489 | * | |
490 | * Memory barrier involvement: | |
491 | * | |
492 | * If desc_read:C reads from desc_reserve:G, then desc_read:E | |
493 | * reads from desc_reserve:F. | |
494 | * | |
495 | * Relies on: | |
496 | * | |
497 | * WMB from desc_reserve:F to desc_reserve:G | |
498 | * matching | |
499 | * RMB from desc_read:C to desc_read:E | |
500 | * | |
501 | * 2. Guarantee the record data is loaded before re-checking the | |
502 | * state. This avoids reading an obsolete descriptor state that may | |
4cfc7258 JO |
503 | * not apply to the copied data. This pairs with data_alloc:A and |
504 | * data_realloc:A. | |
b6cf8b3f JO |
505 | * |
506 | * Memory barrier involvement: | |
507 | * | |
508 | * If copy_data:A reads from data_alloc:B, then desc_read:E | |
509 | * reads from desc_make_reusable:A. | |
510 | * | |
511 | * Relies on: | |
512 | * | |
513 | * MB from desc_make_reusable:A to data_alloc:B | |
514 | * matching | |
515 | * RMB from desc_read:C to desc_read:E | |
516 | * | |
517 | * Note: desc_make_reusable:A and data_alloc:B can be different | |
518 | * CPUs. However, the data_alloc:B CPU (which performs the | |
519 | * full memory barrier) must have previously seen | |
520 | * desc_make_reusable:A. | |
521 | */ | |
522 | smp_rmb(); /* LMM(desc_read:D) */ | |
523 | ||
ce003d67 JO |
524 | /* |
525 | * The data has been copied. Return the current descriptor state, | |
526 | * which may have changed since the load above. | |
527 | */ | |
b6cf8b3f | 528 | state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */ |
ce003d67 JO |
529 | d_state = get_desc_state(id, state_val); |
530 | out: | |
531 | atomic_long_set(&desc_out->state_var, state_val); | |
532 | return d_state; | |
b6cf8b3f JO |
533 | } |
534 | ||
535 | /* | |
4cfc7258 JO |
536 | * Take a specified descriptor out of the finalized state by attempting |
537 | * the transition from finalized to reusable. Either this context or some | |
b6cf8b3f JO |
538 | * other context will have been successful. |
539 | */ | |
540 | static void desc_make_reusable(struct prb_desc_ring *desc_ring, | |
541 | unsigned long id) | |
542 | { | |
4cfc7258 | 543 | unsigned long val_finalized = DESC_SV(id, desc_finalized); |
10dcb06d | 544 | unsigned long val_reusable = DESC_SV(id, desc_reusable); |
b6cf8b3f JO |
545 | struct prb_desc *desc = to_desc(desc_ring, id); |
546 | atomic_long_t *state_var = &desc->state_var; | |
547 | ||
4cfc7258 | 548 | atomic_long_cmpxchg_relaxed(state_var, val_finalized, |
b6cf8b3f JO |
549 | val_reusable); /* LMM(desc_make_reusable:A) */ |
550 | } | |
551 | ||
552 | /* | |
f35efc78 | 553 | * Given the text data ring, put the associated descriptor of each |
b6cf8b3f JO |
554 | * data block from @lpos_begin until @lpos_end into the reusable state. |
555 | * | |
556 | * If there is any problem making the associated descriptor reusable, either | |
4cfc7258 | 557 | * the descriptor has not yet been finalized or another writer context has |
b6cf8b3f JO |
558 | * already pushed the tail lpos past the problematic data block. Regardless, |
559 | * on error the caller can re-load the tail lpos to determine the situation. | |
560 | */ | |
561 | static bool data_make_reusable(struct printk_ringbuffer *rb, | |
b6cf8b3f JO |
562 | unsigned long lpos_begin, |
563 | unsigned long lpos_end, | |
564 | unsigned long *lpos_out) | |
565 | { | |
584da076 NB |
566 | |
567 | struct prb_data_ring *data_ring = &rb->text_data_ring; | |
b6cf8b3f | 568 | struct prb_desc_ring *desc_ring = &rb->desc_ring; |
b6cf8b3f JO |
569 | struct prb_data_block *blk; |
570 | enum desc_state d_state; | |
571 | struct prb_desc desc; | |
f35efc78 | 572 | struct prb_data_blk_lpos *blk_lpos = &desc.text_blk_lpos; |
b6cf8b3f JO |
573 | unsigned long id; |
574 | ||
b6cf8b3f JO |
575 | /* Loop until @lpos_begin has advanced to or beyond @lpos_end. */ |
576 | while ((lpos_end - lpos_begin) - 1 < DATA_SIZE(data_ring)) { | |
577 | blk = to_block(data_ring, lpos_begin); | |
578 | ||
579 | /* | |
580 | * Load the block ID from the data block. This is a data race | |
581 | * against a writer that may have newly reserved this data | |
582 | * area. If the loaded value matches a valid descriptor ID, | |
583 | * the blk_lpos of that descriptor will be checked to make | |
584 | * sure it points back to this data block. If the check fails, | |
585 | * the data area has been recycled by another writer. | |
586 | */ | |
587 | id = blk->id; /* LMM(data_make_reusable:A) */ | |
588 | ||
cfe2790b JO |
589 | d_state = desc_read(desc_ring, id, &desc, |
590 | NULL, NULL); /* LMM(data_make_reusable:B) */ | |
b6cf8b3f JO |
591 | |
592 | switch (d_state) { | |
593 | case desc_miss: | |
b6cf8b3f | 594 | case desc_reserved: |
b6cf8b3f | 595 | case desc_committed: |
4cfc7258 JO |
596 | return false; |
597 | case desc_finalized: | |
b6cf8b3f JO |
598 | /* |
599 | * This data block is invalid if the descriptor | |
600 | * does not point back to it. | |
601 | */ | |
602 | if (blk_lpos->begin != lpos_begin) | |
603 | return false; | |
604 | desc_make_reusable(desc_ring, id); | |
605 | break; | |
606 | case desc_reusable: | |
607 | /* | |
608 | * This data block is invalid if the descriptor | |
609 | * does not point back to it. | |
610 | */ | |
611 | if (blk_lpos->begin != lpos_begin) | |
612 | return false; | |
613 | break; | |
614 | } | |
615 | ||
616 | /* Advance @lpos_begin to the next data block. */ | |
617 | lpos_begin = blk_lpos->next; | |
618 | } | |
619 | ||
620 | *lpos_out = lpos_begin; | |
621 | return true; | |
622 | } | |
623 | ||
624 | /* | |
625 | * Advance the data ring tail to at least @lpos. This function puts | |
626 | * descriptors into the reusable state if the tail is pushed beyond | |
627 | * their associated data block. | |
628 | */ | |
584da076 | 629 | static bool data_push_tail(struct printk_ringbuffer *rb, unsigned long lpos) |
b6cf8b3f | 630 | { |
584da076 | 631 | struct prb_data_ring *data_ring = &rb->text_data_ring; |
b6cf8b3f JO |
632 | unsigned long tail_lpos_new; |
633 | unsigned long tail_lpos; | |
634 | unsigned long next_lpos; | |
635 | ||
d397820f JO |
636 | /* If @lpos is from a data-less block, there is nothing to do. */ |
637 | if (LPOS_DATALESS(lpos)) | |
b6cf8b3f JO |
638 | return true; |
639 | ||
640 | /* | |
641 | * Any descriptor states that have transitioned to reusable due to the | |
642 | * data tail being pushed to this loaded value will be visible to this | |
643 | * CPU. This pairs with data_push_tail:D. | |
644 | * | |
645 | * Memory barrier involvement: | |
646 | * | |
647 | * If data_push_tail:A reads from data_push_tail:D, then this CPU can | |
648 | * see desc_make_reusable:A. | |
649 | * | |
650 | * Relies on: | |
651 | * | |
652 | * MB from desc_make_reusable:A to data_push_tail:D | |
653 | * matches | |
654 | * READFROM from data_push_tail:D to data_push_tail:A | |
655 | * thus | |
656 | * READFROM from desc_make_reusable:A to this CPU | |
657 | */ | |
658 | tail_lpos = atomic_long_read(&data_ring->tail_lpos); /* LMM(data_push_tail:A) */ | |
659 | ||
660 | /* | |
661 | * Loop until the tail lpos is at or beyond @lpos. This condition | |
662 | * may already be satisfied, resulting in no full memory barrier | |
663 | * from data_push_tail:D being performed. However, since this CPU | |
664 | * sees the new tail lpos, any descriptor states that transitioned to | |
665 | * the reusable state must already be visible. | |
666 | */ | |
667 | while ((lpos - tail_lpos) - 1 < DATA_SIZE(data_ring)) { | |
668 | /* | |
669 | * Make all descriptors reusable that are associated with | |
670 | * data blocks before @lpos. | |
671 | */ | |
584da076 | 672 | if (!data_make_reusable(rb, tail_lpos, lpos, &next_lpos)) { |
b6cf8b3f JO |
673 | /* |
674 | * 1. Guarantee the block ID loaded in | |
675 | * data_make_reusable() is performed before | |
676 | * reloading the tail lpos. The failed | |
677 | * data_make_reusable() may be due to a newly | |
678 | * recycled data area causing the tail lpos to | |
679 | * have been previously pushed. This pairs with | |
4cfc7258 | 680 | * data_alloc:A and data_realloc:A. |
b6cf8b3f JO |
681 | * |
682 | * Memory barrier involvement: | |
683 | * | |
684 | * If data_make_reusable:A reads from data_alloc:B, | |
685 | * then data_push_tail:C reads from | |
686 | * data_push_tail:D. | |
687 | * | |
688 | * Relies on: | |
689 | * | |
690 | * MB from data_push_tail:D to data_alloc:B | |
691 | * matching | |
692 | * RMB from data_make_reusable:A to | |
693 | * data_push_tail:C | |
694 | * | |
695 | * Note: data_push_tail:D and data_alloc:B can be | |
696 | * different CPUs. However, the data_alloc:B | |
697 | * CPU (which performs the full memory | |
698 | * barrier) must have previously seen | |
699 | * data_push_tail:D. | |
700 | * | |
701 | * 2. Guarantee the descriptor state loaded in | |
702 | * data_make_reusable() is performed before | |
703 | * reloading the tail lpos. The failed | |
704 | * data_make_reusable() may be due to a newly | |
705 | * recycled descriptor causing the tail lpos to | |
706 | * have been previously pushed. This pairs with | |
707 | * desc_reserve:D. | |
708 | * | |
709 | * Memory barrier involvement: | |
710 | * | |
711 | * If data_make_reusable:B reads from | |
712 | * desc_reserve:F, then data_push_tail:C reads | |
713 | * from data_push_tail:D. | |
714 | * | |
715 | * Relies on: | |
716 | * | |
717 | * MB from data_push_tail:D to desc_reserve:F | |
718 | * matching | |
719 | * RMB from data_make_reusable:B to | |
720 | * data_push_tail:C | |
721 | * | |
722 | * Note: data_push_tail:D and desc_reserve:F can | |
723 | * be different CPUs. However, the | |
724 | * desc_reserve:F CPU (which performs the | |
725 | * full memory barrier) must have previously | |
726 | * seen data_push_tail:D. | |
727 | */ | |
728 | smp_rmb(); /* LMM(data_push_tail:B) */ | |
729 | ||
730 | tail_lpos_new = atomic_long_read(&data_ring->tail_lpos | |
731 | ); /* LMM(data_push_tail:C) */ | |
732 | if (tail_lpos_new == tail_lpos) | |
733 | return false; | |
734 | ||
735 | /* Another CPU pushed the tail. Try again. */ | |
736 | tail_lpos = tail_lpos_new; | |
737 | continue; | |
738 | } | |
739 | ||
740 | /* | |
741 | * Guarantee any descriptor states that have transitioned to | |
742 | * reusable are stored before pushing the tail lpos. A full | |
743 | * memory barrier is needed since other CPUs may have made | |
744 | * the descriptor states reusable. This pairs with | |
745 | * data_push_tail:A. | |
746 | */ | |
747 | if (atomic_long_try_cmpxchg(&data_ring->tail_lpos, &tail_lpos, | |
748 | next_lpos)) { /* LMM(data_push_tail:D) */ | |
749 | break; | |
750 | } | |
751 | } | |
752 | ||
753 | return true; | |
754 | } | |
755 | ||
756 | /* | |
757 | * Advance the desc ring tail. This function advances the tail by one | |
758 | * descriptor, thus invalidating the oldest descriptor. Before advancing | |
759 | * the tail, the tail descriptor is made reusable and all data blocks up to | |
760 | * and including the descriptor's data block are invalidated (i.e. the data | |
761 | * ring tail is pushed past the data block of the descriptor being made | |
762 | * reusable). | |
763 | */ | |
764 | static bool desc_push_tail(struct printk_ringbuffer *rb, | |
765 | unsigned long tail_id) | |
766 | { | |
767 | struct prb_desc_ring *desc_ring = &rb->desc_ring; | |
768 | enum desc_state d_state; | |
769 | struct prb_desc desc; | |
770 | ||
cfe2790b | 771 | d_state = desc_read(desc_ring, tail_id, &desc, NULL, NULL); |
b6cf8b3f JO |
772 | |
773 | switch (d_state) { | |
774 | case desc_miss: | |
775 | /* | |
776 | * If the ID is exactly 1 wrap behind the expected, it is | |
777 | * in the process of being reserved by another writer and | |
778 | * must be considered reserved. | |
779 | */ | |
780 | if (DESC_ID(atomic_long_read(&desc.state_var)) == | |
781 | DESC_ID_PREV_WRAP(desc_ring, tail_id)) { | |
782 | return false; | |
783 | } | |
784 | ||
785 | /* | |
786 | * The ID has changed. Another writer must have pushed the | |
787 | * tail and recycled the descriptor already. Success is | |
788 | * returned because the caller is only interested in the | |
789 | * specified tail being pushed, which it was. | |
790 | */ | |
791 | return true; | |
792 | case desc_reserved: | |
b6cf8b3f | 793 | case desc_committed: |
4cfc7258 JO |
794 | return false; |
795 | case desc_finalized: | |
b6cf8b3f JO |
796 | desc_make_reusable(desc_ring, tail_id); |
797 | break; | |
798 | case desc_reusable: | |
799 | break; | |
800 | } | |
801 | ||
802 | /* | |
803 | * Data blocks must be invalidated before their associated | |
804 | * descriptor can be made available for recycling. Invalidating | |
805 | * them later is not possible because there is no way to trust | |
806 | * data blocks once their associated descriptor is gone. | |
807 | */ | |
808 | ||
584da076 | 809 | if (!data_push_tail(rb, desc.text_blk_lpos.next)) |
b6cf8b3f | 810 | return false; |
b6cf8b3f JO |
811 | |
812 | /* | |
813 | * Check the next descriptor after @tail_id before pushing the tail | |
4cfc7258 | 814 | * to it because the tail must always be in a finalized or reusable |
b6cf8b3f JO |
815 | * state. The implementation of prb_first_seq() relies on this. |
816 | * | |
817 | * A successful read implies that the next descriptor is less than or | |
818 | * equal to @head_id so there is no risk of pushing the tail past the | |
819 | * head. | |
820 | */ | |
cfe2790b JO |
821 | d_state = desc_read(desc_ring, DESC_ID(tail_id + 1), &desc, |
822 | NULL, NULL); /* LMM(desc_push_tail:A) */ | |
b6cf8b3f | 823 | |
4cfc7258 | 824 | if (d_state == desc_finalized || d_state == desc_reusable) { |
b6cf8b3f JO |
825 | /* |
826 | * Guarantee any descriptor states that have transitioned to | |
827 | * reusable are stored before pushing the tail ID. This allows | |
828 | * verifying the recycled descriptor state. A full memory | |
829 | * barrier is needed since other CPUs may have made the | |
830 | * descriptor states reusable. This pairs with desc_reserve:D. | |
831 | */ | |
832 | atomic_long_cmpxchg(&desc_ring->tail_id, tail_id, | |
833 | DESC_ID(tail_id + 1)); /* LMM(desc_push_tail:B) */ | |
834 | } else { | |
835 | /* | |
836 | * Guarantee the last state load from desc_read() is before | |
837 | * reloading @tail_id in order to see a new tail ID in the | |
838 | * case that the descriptor has been recycled. This pairs | |
839 | * with desc_reserve:D. | |
840 | * | |
841 | * Memory barrier involvement: | |
842 | * | |
843 | * If desc_push_tail:A reads from desc_reserve:F, then | |
844 | * desc_push_tail:D reads from desc_push_tail:B. | |
845 | * | |
846 | * Relies on: | |
847 | * | |
848 | * MB from desc_push_tail:B to desc_reserve:F | |
849 | * matching | |
850 | * RMB from desc_push_tail:A to desc_push_tail:D | |
851 | * | |
852 | * Note: desc_push_tail:B and desc_reserve:F can be different | |
853 | * CPUs. However, the desc_reserve:F CPU (which performs | |
854 | * the full memory barrier) must have previously seen | |
855 | * desc_push_tail:B. | |
856 | */ | |
857 | smp_rmb(); /* LMM(desc_push_tail:C) */ | |
858 | ||
859 | /* | |
860 | * Re-check the tail ID. The descriptor following @tail_id is | |
861 | * not in an allowed tail state. But if the tail has since | |
862 | * been moved by another CPU, then it does not matter. | |
863 | */ | |
864 | if (atomic_long_read(&desc_ring->tail_id) == tail_id) /* LMM(desc_push_tail:D) */ | |
865 | return false; | |
866 | } | |
867 | ||
868 | return true; | |
869 | } | |
870 | ||
871 | /* Reserve a new descriptor, invalidating the oldest if necessary. */ | |
872 | static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out) | |
873 | { | |
874 | struct prb_desc_ring *desc_ring = &rb->desc_ring; | |
875 | unsigned long prev_state_val; | |
876 | unsigned long id_prev_wrap; | |
877 | struct prb_desc *desc; | |
878 | unsigned long head_id; | |
879 | unsigned long id; | |
880 | ||
881 | head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */ | |
882 | ||
883 | do { | |
b6cf8b3f JO |
884 | id = DESC_ID(head_id + 1); |
885 | id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id); | |
886 | ||
887 | /* | |
888 | * Guarantee the head ID is read before reading the tail ID. | |
889 | * Since the tail ID is updated before the head ID, this | |
890 | * guarantees that @id_prev_wrap is never ahead of the tail | |
891 | * ID. This pairs with desc_reserve:D. | |
892 | * | |
893 | * Memory barrier involvement: | |
894 | * | |
895 | * If desc_reserve:A reads from desc_reserve:D, then | |
896 | * desc_reserve:C reads from desc_push_tail:B. | |
897 | * | |
898 | * Relies on: | |
899 | * | |
900 | * MB from desc_push_tail:B to desc_reserve:D | |
901 | * matching | |
902 | * RMB from desc_reserve:A to desc_reserve:C | |
903 | * | |
904 | * Note: desc_push_tail:B and desc_reserve:D can be different | |
905 | * CPUs. However, the desc_reserve:D CPU (which performs | |
906 | * the full memory barrier) must have previously seen | |
907 | * desc_push_tail:B. | |
908 | */ | |
909 | smp_rmb(); /* LMM(desc_reserve:B) */ | |
910 | ||
911 | if (id_prev_wrap == atomic_long_read(&desc_ring->tail_id | |
912 | )) { /* LMM(desc_reserve:C) */ | |
913 | /* | |
914 | * Make space for the new descriptor by | |
915 | * advancing the tail. | |
916 | */ | |
917 | if (!desc_push_tail(rb, id_prev_wrap)) | |
918 | return false; | |
919 | } | |
920 | ||
921 | /* | |
922 | * 1. Guarantee the tail ID is read before validating the | |
923 | * recycled descriptor state. A read memory barrier is | |
924 | * sufficient for this. This pairs with desc_push_tail:B. | |
925 | * | |
926 | * Memory barrier involvement: | |
927 | * | |
928 | * If desc_reserve:C reads from desc_push_tail:B, then | |
929 | * desc_reserve:E reads from desc_make_reusable:A. | |
930 | * | |
931 | * Relies on: | |
932 | * | |
933 | * MB from desc_make_reusable:A to desc_push_tail:B | |
934 | * matching | |
935 | * RMB from desc_reserve:C to desc_reserve:E | |
936 | * | |
937 | * Note: desc_make_reusable:A and desc_push_tail:B can be | |
938 | * different CPUs. However, the desc_push_tail:B CPU | |
939 | * (which performs the full memory barrier) must have | |
940 | * previously seen desc_make_reusable:A. | |
941 | * | |
942 | * 2. Guarantee the tail ID is stored before storing the head | |
943 | * ID. This pairs with desc_reserve:B. | |
944 | * | |
945 | * 3. Guarantee any data ring tail changes are stored before | |
946 | * recycling the descriptor. Data ring tail changes can | |
947 | * happen via desc_push_tail()->data_push_tail(). A full | |
948 | * memory barrier is needed since another CPU may have | |
949 | * pushed the data ring tails. This pairs with | |
950 | * data_push_tail:B. | |
951 | * | |
952 | * 4. Guarantee a new tail ID is stored before recycling the | |
953 | * descriptor. A full memory barrier is needed since | |
954 | * another CPU may have pushed the tail ID. This pairs | |
955 | * with desc_push_tail:C and this also pairs with | |
956 | * prb_first_seq:C. | |
4cfc7258 JO |
957 | * |
958 | * 5. Guarantee the head ID is stored before trying to | |
959 | * finalize the previous descriptor. This pairs with | |
960 | * _prb_commit:B. | |
b6cf8b3f JO |
961 | */ |
962 | } while (!atomic_long_try_cmpxchg(&desc_ring->head_id, &head_id, | |
963 | id)); /* LMM(desc_reserve:D) */ | |
964 | ||
965 | desc = to_desc(desc_ring, id); | |
966 | ||
967 | /* | |
968 | * If the descriptor has been recycled, verify the old state val. | |
969 | * See "ABA Issues" about why this verification is performed. | |
970 | */ | |
971 | prev_state_val = atomic_long_read(&desc->state_var); /* LMM(desc_reserve:E) */ | |
972 | if (prev_state_val && | |
10dcb06d | 973 | get_desc_state(id_prev_wrap, prev_state_val) != desc_reusable) { |
b6cf8b3f JO |
974 | WARN_ON_ONCE(1); |
975 | return false; | |
976 | } | |
977 | ||
978 | /* | |
979 | * Assign the descriptor a new ID and set its state to reserved. | |
980 | * See "ABA Issues" about why cmpxchg() instead of set() is used. | |
981 | * | |
982 | * Guarantee the new descriptor ID and state is stored before making | |
983 | * any other changes. A write memory barrier is sufficient for this. | |
984 | * This pairs with desc_read:D. | |
985 | */ | |
986 | if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val, | |
10dcb06d | 987 | DESC_SV(id, desc_reserved))) { /* LMM(desc_reserve:F) */ |
b6cf8b3f JO |
988 | WARN_ON_ONCE(1); |
989 | return false; | |
990 | } | |
991 | ||
992 | /* Now data in @desc can be modified: LMM(desc_reserve:G) */ | |
993 | ||
994 | *id_out = id; | |
995 | return true; | |
996 | } | |
997 | ||
998 | /* Determine the end of a data block. */ | |
999 | static unsigned long get_next_lpos(struct prb_data_ring *data_ring, | |
1000 | unsigned long lpos, unsigned int size) | |
1001 | { | |
1002 | unsigned long begin_lpos; | |
1003 | unsigned long next_lpos; | |
1004 | ||
1005 | begin_lpos = lpos; | |
1006 | next_lpos = lpos + size; | |
1007 | ||
1008 | /* First check if the data block does not wrap. */ | |
1009 | if (DATA_WRAPS(data_ring, begin_lpos) == DATA_WRAPS(data_ring, next_lpos)) | |
1010 | return next_lpos; | |
1011 | ||
1012 | /* Wrapping data blocks store their data at the beginning. */ | |
1013 | return (DATA_THIS_WRAP_START_LPOS(data_ring, next_lpos) + size); | |
1014 | } | |
1015 | ||
1016 | /* | |
1017 | * Allocate a new data block, invalidating the oldest data block(s) | |
1018 | * if necessary. This function also associates the data block with | |
1019 | * a specified descriptor. | |
1020 | */ | |
584da076 | 1021 | static char *data_alloc(struct printk_ringbuffer *rb, unsigned int size, |
b6cf8b3f JO |
1022 | struct prb_data_blk_lpos *blk_lpos, unsigned long id) |
1023 | { | |
584da076 | 1024 | struct prb_data_ring *data_ring = &rb->text_data_ring; |
b6cf8b3f JO |
1025 | struct prb_data_block *blk; |
1026 | unsigned long begin_lpos; | |
1027 | unsigned long next_lpos; | |
1028 | ||
1029 | if (size == 0) { | |
1030 | /* Specify a data-less block. */ | |
d397820f JO |
1031 | blk_lpos->begin = NO_LPOS; |
1032 | blk_lpos->next = NO_LPOS; | |
b6cf8b3f JO |
1033 | return NULL; |
1034 | } | |
1035 | ||
1036 | size = to_blk_size(size); | |
1037 | ||
1038 | begin_lpos = atomic_long_read(&data_ring->head_lpos); | |
1039 | ||
1040 | do { | |
1041 | next_lpos = get_next_lpos(data_ring, begin_lpos, size); | |
1042 | ||
584da076 | 1043 | if (!data_push_tail(rb, next_lpos - DATA_SIZE(data_ring))) { |
b6cf8b3f | 1044 | /* Failed to allocate, specify a data-less block. */ |
d397820f JO |
1045 | blk_lpos->begin = FAILED_LPOS; |
1046 | blk_lpos->next = FAILED_LPOS; | |
b6cf8b3f JO |
1047 | return NULL; |
1048 | } | |
1049 | ||
1050 | /* | |
1051 | * 1. Guarantee any descriptor states that have transitioned | |
1052 | * to reusable are stored before modifying the newly | |
1053 | * allocated data area. A full memory barrier is needed | |
1054 | * since other CPUs may have made the descriptor states | |
1055 | * reusable. See data_push_tail:A about why the reusable | |
1056 | * states are visible. This pairs with desc_read:D. | |
1057 | * | |
1058 | * 2. Guarantee any updated tail lpos is stored before | |
1059 | * modifying the newly allocated data area. Another CPU may | |
1060 | * be in data_make_reusable() and is reading a block ID | |
1061 | * from this area. data_make_reusable() can handle reading | |
1062 | * a garbage block ID value, but then it must be able to | |
1063 | * load a new tail lpos. A full memory barrier is needed | |
1064 | * since other CPUs may have updated the tail lpos. This | |
1065 | * pairs with data_push_tail:B. | |
1066 | */ | |
1067 | } while (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &begin_lpos, | |
1068 | next_lpos)); /* LMM(data_alloc:A) */ | |
1069 | ||
1070 | blk = to_block(data_ring, begin_lpos); | |
1071 | blk->id = id; /* LMM(data_alloc:B) */ | |
1072 | ||
1073 | if (DATA_WRAPS(data_ring, begin_lpos) != DATA_WRAPS(data_ring, next_lpos)) { | |
1074 | /* Wrapping data blocks store their data at the beginning. */ | |
1075 | blk = to_block(data_ring, 0); | |
1076 | ||
1077 | /* | |
1078 | * Store the ID on the wrapped block for consistency. | |
1079 | * The printk_ringbuffer does not actually use it. | |
1080 | */ | |
1081 | blk->id = id; | |
1082 | } | |
1083 | ||
1084 | blk_lpos->begin = begin_lpos; | |
1085 | blk_lpos->next = next_lpos; | |
1086 | ||
1087 | return &blk->data[0]; | |
1088 | } | |
1089 | ||
4cfc7258 JO |
1090 | /* |
1091 | * Try to resize an existing data block associated with the descriptor | |
1092 | * specified by @id. If the resized data block should become wrapped, it | |
1093 | * copies the old data to the new data block. If @size yields a data block | |
1094 | * with the same or less size, the data block is left as is. | |
1095 | * | |
1096 | * Fail if this is not the last allocated data block or if there is not | |
1097 | * enough space or it is not possible make enough space. | |
1098 | * | |
1099 | * Return a pointer to the beginning of the entire data buffer or NULL on | |
1100 | * failure. | |
1101 | */ | |
584da076 | 1102 | static char *data_realloc(struct printk_ringbuffer *rb, unsigned int size, |
4cfc7258 JO |
1103 | struct prb_data_blk_lpos *blk_lpos, unsigned long id) |
1104 | { | |
584da076 | 1105 | struct prb_data_ring *data_ring = &rb->text_data_ring; |
4cfc7258 JO |
1106 | struct prb_data_block *blk; |
1107 | unsigned long head_lpos; | |
1108 | unsigned long next_lpos; | |
1109 | bool wrapped; | |
1110 | ||
1111 | /* Reallocation only works if @blk_lpos is the newest data block. */ | |
1112 | head_lpos = atomic_long_read(&data_ring->head_lpos); | |
1113 | if (head_lpos != blk_lpos->next) | |
1114 | return NULL; | |
1115 | ||
1116 | /* Keep track if @blk_lpos was a wrapping data block. */ | |
1117 | wrapped = (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, blk_lpos->next)); | |
1118 | ||
1119 | size = to_blk_size(size); | |
1120 | ||
1121 | next_lpos = get_next_lpos(data_ring, blk_lpos->begin, size); | |
1122 | ||
1123 | /* If the data block does not increase, there is nothing to do. */ | |
1124 | if (head_lpos - next_lpos < DATA_SIZE(data_ring)) { | |
eac48eb6 PM |
1125 | if (wrapped) |
1126 | blk = to_block(data_ring, 0); | |
1127 | else | |
1128 | blk = to_block(data_ring, blk_lpos->begin); | |
4cfc7258 JO |
1129 | return &blk->data[0]; |
1130 | } | |
1131 | ||
584da076 | 1132 | if (!data_push_tail(rb, next_lpos - DATA_SIZE(data_ring))) |
4cfc7258 JO |
1133 | return NULL; |
1134 | ||
1135 | /* The memory barrier involvement is the same as data_alloc:A. */ | |
1136 | if (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &head_lpos, | |
1137 | next_lpos)) { /* LMM(data_realloc:A) */ | |
1138 | return NULL; | |
1139 | } | |
1140 | ||
1141 | blk = to_block(data_ring, blk_lpos->begin); | |
1142 | ||
1143 | if (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, next_lpos)) { | |
1144 | struct prb_data_block *old_blk = blk; | |
1145 | ||
1146 | /* Wrapping data blocks store their data at the beginning. */ | |
1147 | blk = to_block(data_ring, 0); | |
1148 | ||
1149 | /* | |
1150 | * Store the ID on the wrapped block for consistency. | |
1151 | * The printk_ringbuffer does not actually use it. | |
1152 | */ | |
1153 | blk->id = id; | |
1154 | ||
1155 | if (!wrapped) { | |
1156 | /* | |
1157 | * Since the allocated space is now in the newly | |
1158 | * created wrapping data block, copy the content | |
1159 | * from the old data block. | |
1160 | */ | |
1161 | memcpy(&blk->data[0], &old_blk->data[0], | |
1162 | (blk_lpos->next - blk_lpos->begin) - sizeof(blk->id)); | |
1163 | } | |
1164 | } | |
1165 | ||
1166 | blk_lpos->next = next_lpos; | |
1167 | ||
1168 | return &blk->data[0]; | |
1169 | } | |
1170 | ||
b6cf8b3f JO |
1171 | /* Return the number of bytes used by a data block. */ |
1172 | static unsigned int space_used(struct prb_data_ring *data_ring, | |
1173 | struct prb_data_blk_lpos *blk_lpos) | |
1174 | { | |
d397820f | 1175 | /* Data-less blocks take no space. */ |
e3bc0401 | 1176 | if (BLK_DATALESS(blk_lpos)) |
d397820f JO |
1177 | return 0; |
1178 | ||
b6cf8b3f JO |
1179 | if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) { |
1180 | /* Data block does not wrap. */ | |
1181 | return (DATA_INDEX(data_ring, blk_lpos->next) - | |
1182 | DATA_INDEX(data_ring, blk_lpos->begin)); | |
1183 | } | |
1184 | ||
1185 | /* | |
1186 | * For wrapping data blocks, the trailing (wasted) space is | |
1187 | * also counted. | |
1188 | */ | |
1189 | return (DATA_INDEX(data_ring, blk_lpos->next) + | |
1190 | DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin)); | |
1191 | } | |
1192 | ||
2a7f87ed JO |
1193 | /* |
1194 | * Given @blk_lpos, return a pointer to the writer data from the data block | |
1195 | * and calculate the size of the data part. A NULL pointer is returned if | |
1196 | * @blk_lpos specifies values that could never be legal. | |
1197 | * | |
1198 | * This function (used by readers) performs strict validation on the lpos | |
1199 | * values to possibly detect bugs in the writer code. A WARN_ON_ONCE() is | |
1200 | * triggered if an internal error is detected. | |
1201 | */ | |
1202 | static const char *get_data(struct prb_data_ring *data_ring, | |
1203 | struct prb_data_blk_lpos *blk_lpos, | |
1204 | unsigned int *data_size) | |
1205 | { | |
1206 | struct prb_data_block *db; | |
1207 | ||
1208 | /* Data-less data block description. */ | |
e3bc0401 | 1209 | if (BLK_DATALESS(blk_lpos)) { |
2a7f87ed JO |
1210 | if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) { |
1211 | *data_size = 0; | |
1212 | return ""; | |
1213 | } | |
1214 | return NULL; | |
1215 | } | |
1216 | ||
1217 | /* Regular data block: @begin less than @next and in same wrap. */ | |
1218 | if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) && | |
1219 | blk_lpos->begin < blk_lpos->next) { | |
1220 | db = to_block(data_ring, blk_lpos->begin); | |
1221 | *data_size = blk_lpos->next - blk_lpos->begin; | |
1222 | ||
1223 | /* Wrapping data block: @begin is one wrap behind @next. */ | |
1224 | } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) == | |
1225 | DATA_WRAPS(data_ring, blk_lpos->next)) { | |
1226 | db = to_block(data_ring, 0); | |
1227 | *data_size = DATA_INDEX(data_ring, blk_lpos->next); | |
1228 | ||
1229 | /* Illegal block description. */ | |
1230 | } else { | |
1231 | WARN_ON_ONCE(1); | |
1232 | return NULL; | |
1233 | } | |
1234 | ||
1235 | /* A valid data block will always be aligned to the ID size. */ | |
1236 | if (WARN_ON_ONCE(blk_lpos->begin != ALIGN(blk_lpos->begin, sizeof(db->id))) || | |
1237 | WARN_ON_ONCE(blk_lpos->next != ALIGN(blk_lpos->next, sizeof(db->id)))) { | |
1238 | return NULL; | |
1239 | } | |
1240 | ||
1241 | /* A valid data block will always have at least an ID. */ | |
1242 | if (WARN_ON_ONCE(*data_size < sizeof(db->id))) | |
1243 | return NULL; | |
1244 | ||
1245 | /* Subtract block ID space from size to reflect data size. */ | |
1246 | *data_size -= sizeof(db->id); | |
1247 | ||
1248 | return &db->data[0]; | |
1249 | } | |
1250 | ||
4cfc7258 JO |
1251 | /* |
1252 | * Attempt to transition the newest descriptor from committed back to reserved | |
1253 | * so that the record can be modified by a writer again. This is only possible | |
1254 | * if the descriptor is not yet finalized and the provided @caller_id matches. | |
1255 | */ | |
1256 | static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring, | |
1257 | u32 caller_id, unsigned long *id_out) | |
1258 | { | |
1259 | unsigned long prev_state_val; | |
1260 | enum desc_state d_state; | |
1261 | struct prb_desc desc; | |
1262 | struct prb_desc *d; | |
1263 | unsigned long id; | |
cfe2790b | 1264 | u32 cid; |
4cfc7258 JO |
1265 | |
1266 | id = atomic_long_read(&desc_ring->head_id); | |
1267 | ||
1268 | /* | |
1269 | * To reduce unnecessarily reopening, first check if the descriptor | |
1270 | * state and caller ID are correct. | |
1271 | */ | |
cfe2790b JO |
1272 | d_state = desc_read(desc_ring, id, &desc, NULL, &cid); |
1273 | if (d_state != desc_committed || cid != caller_id) | |
4cfc7258 JO |
1274 | return NULL; |
1275 | ||
1276 | d = to_desc(desc_ring, id); | |
1277 | ||
1278 | prev_state_val = DESC_SV(id, desc_committed); | |
1279 | ||
1280 | /* | |
1281 | * Guarantee the reserved state is stored before reading any | |
1282 | * record data. A full memory barrier is needed because @state_var | |
1283 | * modification is followed by reading. This pairs with _prb_commit:B. | |
1284 | * | |
1285 | * Memory barrier involvement: | |
1286 | * | |
1287 | * If desc_reopen_last:A reads from _prb_commit:B, then | |
1288 | * prb_reserve_in_last:A reads from _prb_commit:A. | |
1289 | * | |
1290 | * Relies on: | |
1291 | * | |
1292 | * WMB from _prb_commit:A to _prb_commit:B | |
1293 | * matching | |
1294 | * MB If desc_reopen_last:A to prb_reserve_in_last:A | |
1295 | */ | |
1296 | if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val, | |
1297 | DESC_SV(id, desc_reserved))) { /* LMM(desc_reopen_last:A) */ | |
1298 | return NULL; | |
1299 | } | |
1300 | ||
1301 | *id_out = id; | |
1302 | return d; | |
1303 | } | |
1304 | ||
1305 | /** | |
1306 | * prb_reserve_in_last() - Re-reserve and extend the space in the ringbuffer | |
1307 | * used by the newest record. | |
1308 | * | |
1309 | * @e: The entry structure to setup. | |
1310 | * @rb: The ringbuffer to re-reserve and extend data in. | |
1311 | * @r: The record structure to allocate buffers for. | |
1312 | * @caller_id: The caller ID of the caller (reserving writer). | |
59f8bcca | 1313 | * @max_size: Fail if the extended size would be greater than this. |
4cfc7258 JO |
1314 | * |
1315 | * This is the public function available to writers to re-reserve and extend | |
1316 | * data. | |
1317 | * | |
1318 | * The writer specifies the text size to extend (not the new total size) by | |
f35efc78 JO |
1319 | * setting the @text_buf_size field of @r. To ensure proper initialization |
1320 | * of @r, prb_rec_init_wr() should be used. | |
4cfc7258 JO |
1321 | * |
1322 | * This function will fail if @caller_id does not match the caller ID of the | |
1323 | * newest record. In that case the caller must reserve new data using | |
1324 | * prb_reserve(). | |
1325 | * | |
1326 | * Context: Any context. Disables local interrupts on success. | |
1327 | * Return: true if text data could be extended, otherwise false. | |
1328 | * | |
1329 | * On success: | |
1330 | * | |
1331 | * - @r->text_buf points to the beginning of the entire text buffer. | |
1332 | * | |
1333 | * - @r->text_buf_size is set to the new total size of the buffer. | |
1334 | * | |
4cfc7258 JO |
1335 | * - @r->info is not touched so that @r->info->text_len could be used |
1336 | * to append the text. | |
1337 | * | |
1338 | * - prb_record_text_space() can be used on @e to query the new | |
1339 | * actually used space. | |
1340 | * | |
1341 | * Important: All @r->info fields will already be set with the current values | |
1342 | * for the record. I.e. @r->info->text_len will be less than | |
f35efc78 | 1343 | * @text_buf_size. Writers can use @r->info->text_len to know |
4cfc7258 JO |
1344 | * where concatenation begins and writers should update |
1345 | * @r->info->text_len after concatenating. | |
1346 | */ | |
1347 | bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, | |
59f8bcca | 1348 | struct printk_record *r, u32 caller_id, unsigned int max_size) |
4cfc7258 | 1349 | { |
cfe2790b JO |
1350 | struct prb_desc_ring *desc_ring = &rb->desc_ring; |
1351 | struct printk_info *info; | |
4cfc7258 JO |
1352 | unsigned int data_size; |
1353 | struct prb_desc *d; | |
1354 | unsigned long id; | |
1355 | ||
1356 | local_irq_save(e->irqflags); | |
1357 | ||
1358 | /* Transition the newest descriptor back to the reserved state. */ | |
cfe2790b | 1359 | d = desc_reopen_last(desc_ring, caller_id, &id); |
4cfc7258 JO |
1360 | if (!d) { |
1361 | local_irq_restore(e->irqflags); | |
1362 | goto fail_reopen; | |
1363 | } | |
1364 | ||
1365 | /* Now the writer has exclusive access: LMM(prb_reserve_in_last:A) */ | |
1366 | ||
cfe2790b JO |
1367 | info = to_info(desc_ring, id); |
1368 | ||
4cfc7258 JO |
1369 | /* |
1370 | * Set the @e fields here so that prb_commit() can be used if | |
1371 | * anything fails from now on. | |
1372 | */ | |
1373 | e->rb = rb; | |
1374 | e->id = id; | |
1375 | ||
1376 | /* | |
1377 | * desc_reopen_last() checked the caller_id, but there was no | |
1378 | * exclusive access at that point. The descriptor may have | |
1379 | * changed since then. | |
1380 | */ | |
cfe2790b | 1381 | if (caller_id != info->caller_id) |
4cfc7258 JO |
1382 | goto fail; |
1383 | ||
1384 | if (BLK_DATALESS(&d->text_blk_lpos)) { | |
cfe2790b | 1385 | if (WARN_ON_ONCE(info->text_len != 0)) { |
4cfc7258 | 1386 | pr_warn_once("wrong text_len value (%hu, expecting 0)\n", |
cfe2790b JO |
1387 | info->text_len); |
1388 | info->text_len = 0; | |
4cfc7258 JO |
1389 | } |
1390 | ||
1391 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) | |
1392 | goto fail; | |
1393 | ||
59f8bcca JO |
1394 | if (r->text_buf_size > max_size) |
1395 | goto fail; | |
1396 | ||
584da076 | 1397 | r->text_buf = data_alloc(rb, r->text_buf_size, |
4cfc7258 JO |
1398 | &d->text_blk_lpos, id); |
1399 | } else { | |
1400 | if (!get_data(&rb->text_data_ring, &d->text_blk_lpos, &data_size)) | |
1401 | goto fail; | |
1402 | ||
1403 | /* | |
1404 | * Increase the buffer size to include the original size. If | |
1405 | * the meta data (@text_len) is not sane, use the full data | |
1406 | * block size. | |
1407 | */ | |
cfe2790b | 1408 | if (WARN_ON_ONCE(info->text_len > data_size)) { |
4cfc7258 | 1409 | pr_warn_once("wrong text_len value (%hu, expecting <=%u)\n", |
cfe2790b JO |
1410 | info->text_len, data_size); |
1411 | info->text_len = data_size; | |
4cfc7258 | 1412 | } |
cfe2790b | 1413 | r->text_buf_size += info->text_len; |
4cfc7258 JO |
1414 | |
1415 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) | |
1416 | goto fail; | |
1417 | ||
59f8bcca JO |
1418 | if (r->text_buf_size > max_size) |
1419 | goto fail; | |
1420 | ||
584da076 | 1421 | r->text_buf = data_realloc(rb, r->text_buf_size, |
4cfc7258 JO |
1422 | &d->text_blk_lpos, id); |
1423 | } | |
1424 | if (r->text_buf_size && !r->text_buf) | |
1425 | goto fail; | |
1426 | ||
cfe2790b | 1427 | r->info = info; |
4cfc7258 JO |
1428 | |
1429 | e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos); | |
1430 | ||
1431 | return true; | |
1432 | fail: | |
1433 | prb_commit(e); | |
1434 | /* prb_commit() re-enabled interrupts. */ | |
1435 | fail_reopen: | |
1436 | /* Make it clear to the caller that the re-reserve failed. */ | |
1437 | memset(r, 0, sizeof(*r)); | |
1438 | return false; | |
1439 | } | |
1440 | ||
1441 | /* | |
1442 | * Attempt to finalize a specified descriptor. If this fails, the descriptor | |
1443 | * is either already final or it will finalize itself when the writer commits. | |
1444 | */ | |
1445 | static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id) | |
1446 | { | |
1447 | unsigned long prev_state_val = DESC_SV(id, desc_committed); | |
1448 | struct prb_desc *d = to_desc(desc_ring, id); | |
1449 | ||
1450 | atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val, | |
1451 | DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */ | |
1452 | } | |
1453 | ||
b6cf8b3f JO |
1454 | /** |
1455 | * prb_reserve() - Reserve space in the ringbuffer. | |
1456 | * | |
1457 | * @e: The entry structure to setup. | |
1458 | * @rb: The ringbuffer to reserve data in. | |
1459 | * @r: The record structure to allocate buffers for. | |
1460 | * | |
1461 | * This is the public function available to writers to reserve data. | |
1462 | * | |
f35efc78 JO |
1463 | * The writer specifies the text size to reserve by setting the |
1464 | * @text_buf_size field of @r. To ensure proper initialization of @r, | |
1465 | * prb_rec_init_wr() should be used. | |
b6cf8b3f JO |
1466 | * |
1467 | * Context: Any context. Disables local interrupts on success. | |
1468 | * Return: true if at least text data could be allocated, otherwise false. | |
1469 | * | |
f35efc78 JO |
1470 | * On success, the fields @info and @text_buf of @r will be set by this |
1471 | * function and should be filled in by the writer before committing. Also | |
b6cf8b3f JO |
1472 | * on success, prb_record_text_space() can be used on @e to query the actual |
1473 | * space used for the text data block. | |
1474 | * | |
f35efc78 JO |
1475 | * Important: @info->text_len needs to be set correctly by the writer in |
1476 | * order for data to be readable and/or extended. Its value | |
1477 | * is initialized to 0. | |
b6cf8b3f JO |
1478 | */ |
1479 | bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, | |
1480 | struct printk_record *r) | |
1481 | { | |
1482 | struct prb_desc_ring *desc_ring = &rb->desc_ring; | |
cfe2790b | 1483 | struct printk_info *info; |
b6cf8b3f JO |
1484 | struct prb_desc *d; |
1485 | unsigned long id; | |
cc5c7041 | 1486 | u64 seq; |
b6cf8b3f JO |
1487 | |
1488 | if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) | |
1489 | goto fail; | |
1490 | ||
b6cf8b3f JO |
1491 | /* |
1492 | * Descriptors in the reserved state act as blockers to all further | |
1493 | * reservations once the desc_ring has fully wrapped. Disable | |
1494 | * interrupts during the reserve/commit window in order to minimize | |
1495 | * the likelihood of this happening. | |
1496 | */ | |
1497 | local_irq_save(e->irqflags); | |
1498 | ||
1499 | if (!desc_reserve(rb, &id)) { | |
1500 | /* Descriptor reservation failures are tracked. */ | |
1501 | atomic_long_inc(&rb->fail); | |
1502 | local_irq_restore(e->irqflags); | |
1503 | goto fail; | |
1504 | } | |
1505 | ||
1506 | d = to_desc(desc_ring, id); | |
cfe2790b | 1507 | info = to_info(desc_ring, id); |
b6cf8b3f | 1508 | |
cc5c7041 JO |
1509 | /* |
1510 | * All @info fields (except @seq) are cleared and must be filled in | |
1511 | * by the writer. Save @seq before clearing because it is used to | |
1512 | * determine the new sequence number. | |
1513 | */ | |
cfe2790b JO |
1514 | seq = info->seq; |
1515 | memset(info, 0, sizeof(*info)); | |
cc5c7041 | 1516 | |
b6cf8b3f JO |
1517 | /* |
1518 | * Set the @e fields here so that prb_commit() can be used if | |
1519 | * text data allocation fails. | |
1520 | */ | |
1521 | e->rb = rb; | |
1522 | e->id = id; | |
1523 | ||
1524 | /* | |
1525 | * Initialize the sequence number if it has "never been set". | |
1526 | * Otherwise just increment it by a full wrap. | |
1527 | * | |
1528 | * @seq is considered "never been set" if it has a value of 0, | |
cfe2790b | 1529 | * _except_ for @infos[0], which was specially setup by the ringbuffer |
b6cf8b3f JO |
1530 | * initializer and therefore is always considered as set. |
1531 | * | |
1532 | * See the "Bootstrap" comment block in printk_ringbuffer.h for | |
1533 | * details about how the initializer bootstraps the descriptors. | |
1534 | */ | |
cc5c7041 | 1535 | if (seq == 0 && DESC_INDEX(desc_ring, id) != 0) |
cfe2790b | 1536 | info->seq = DESC_INDEX(desc_ring, id); |
b6cf8b3f | 1537 | else |
cfe2790b | 1538 | info->seq = seq + DESCS_COUNT(desc_ring); |
b6cf8b3f | 1539 | |
4cfc7258 JO |
1540 | /* |
1541 | * New data is about to be reserved. Once that happens, previous | |
1542 | * descriptors are no longer able to be extended. Finalize the | |
1543 | * previous descriptor now so that it can be made available to | |
1544 | * readers. (For seq==0 there is no previous descriptor.) | |
1545 | */ | |
cfe2790b | 1546 | if (info->seq > 0) |
4cfc7258 JO |
1547 | desc_make_final(desc_ring, DESC_ID(id - 1)); |
1548 | ||
584da076 | 1549 | r->text_buf = data_alloc(rb, r->text_buf_size, &d->text_blk_lpos, id); |
b6cf8b3f JO |
1550 | /* If text data allocation fails, a data-less record is committed. */ |
1551 | if (r->text_buf_size && !r->text_buf) { | |
b6cf8b3f JO |
1552 | prb_commit(e); |
1553 | /* prb_commit() re-enabled interrupts. */ | |
1554 | goto fail; | |
1555 | } | |
1556 | ||
cfe2790b | 1557 | r->info = info; |
b6cf8b3f | 1558 | |
b6cf8b3f JO |
1559 | /* Record full text space used by record. */ |
1560 | e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos); | |
1561 | ||
1562 | return true; | |
1563 | fail: | |
1564 | /* Make it clear to the caller that the reserve failed. */ | |
1565 | memset(r, 0, sizeof(*r)); | |
1566 | return false; | |
1567 | } | |
1568 | ||
4cfc7258 JO |
1569 | /* Commit the data (possibly finalizing it) and restore interrupts. */ |
1570 | static void _prb_commit(struct prb_reserved_entry *e, unsigned long state_val) | |
b6cf8b3f JO |
1571 | { |
1572 | struct prb_desc_ring *desc_ring = &e->rb->desc_ring; | |
1573 | struct prb_desc *d = to_desc(desc_ring, e->id); | |
10dcb06d | 1574 | unsigned long prev_state_val = DESC_SV(e->id, desc_reserved); |
b6cf8b3f | 1575 | |
4cfc7258 | 1576 | /* Now the writer has finished all writing: LMM(_prb_commit:A) */ |
b6cf8b3f JO |
1577 | |
1578 | /* | |
1579 | * Set the descriptor as committed. See "ABA Issues" about why | |
1580 | * cmpxchg() instead of set() is used. | |
1581 | * | |
4cfc7258 JO |
1582 | * 1 Guarantee all record data is stored before the descriptor state |
1583 | * is stored as committed. A write memory barrier is sufficient | |
1584 | * for this. This pairs with desc_read:B and desc_reopen_last:A. | |
1585 | * | |
1586 | * 2. Guarantee the descriptor state is stored as committed before | |
1587 | * re-checking the head ID in order to possibly finalize this | |
1588 | * descriptor. This pairs with desc_reserve:D. | |
1589 | * | |
1590 | * Memory barrier involvement: | |
1591 | * | |
1592 | * If prb_commit:A reads from desc_reserve:D, then | |
1593 | * desc_make_final:A reads from _prb_commit:B. | |
1594 | * | |
1595 | * Relies on: | |
1596 | * | |
1597 | * MB _prb_commit:B to prb_commit:A | |
1598 | * matching | |
1599 | * MB desc_reserve:D to desc_make_final:A | |
b6cf8b3f JO |
1600 | */ |
1601 | if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val, | |
4cfc7258 | 1602 | DESC_SV(e->id, state_val))) { /* LMM(_prb_commit:B) */ |
b6cf8b3f JO |
1603 | WARN_ON_ONCE(1); |
1604 | } | |
1605 | ||
1606 | /* Restore interrupts, the reserve/commit window is finished. */ | |
1607 | local_irq_restore(e->irqflags); | |
1608 | } | |
1609 | ||
4cfc7258 JO |
1610 | /** |
1611 | * prb_commit() - Commit (previously reserved) data to the ringbuffer. | |
1612 | * | |
1613 | * @e: The entry containing the reserved data information. | |
1614 | * | |
1615 | * This is the public function available to writers to commit data. | |
1616 | * | |
1617 | * Note that the data is not yet available to readers until it is finalized. | |
1618 | * Finalizing happens automatically when space for the next record is | |
1619 | * reserved. | |
1620 | * | |
1621 | * See prb_final_commit() for a version of this function that finalizes | |
1622 | * immediately. | |
1623 | * | |
1624 | * Context: Any context. Enables local interrupts. | |
1625 | */ | |
1626 | void prb_commit(struct prb_reserved_entry *e) | |
1627 | { | |
1628 | struct prb_desc_ring *desc_ring = &e->rb->desc_ring; | |
1629 | unsigned long head_id; | |
1630 | ||
1631 | _prb_commit(e, desc_committed); | |
1632 | ||
1633 | /* | |
1634 | * If this descriptor is no longer the head (i.e. a new record has | |
1635 | * been allocated), extending the data for this record is no longer | |
1636 | * allowed and therefore it must be finalized. | |
1637 | */ | |
1638 | head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_commit:A) */ | |
1639 | if (head_id != e->id) | |
1640 | desc_make_final(desc_ring, e->id); | |
1641 | } | |
1642 | ||
1643 | /** | |
1644 | * prb_final_commit() - Commit and finalize (previously reserved) data to | |
1645 | * the ringbuffer. | |
1646 | * | |
1647 | * @e: The entry containing the reserved data information. | |
1648 | * | |
1649 | * This is the public function available to writers to commit+finalize data. | |
1650 | * | |
1651 | * By finalizing, the data is made immediately available to readers. | |
1652 | * | |
1653 | * This function should only be used if there are no intentions of extending | |
1654 | * this data using prb_reserve_in_last(). | |
1655 | * | |
1656 | * Context: Any context. Enables local interrupts. | |
1657 | */ | |
1658 | void prb_final_commit(struct prb_reserved_entry *e) | |
1659 | { | |
1660 | _prb_commit(e, desc_finalized); | |
1661 | } | |
1662 | ||
b6cf8b3f JO |
1663 | /* |
1664 | * Count the number of lines in provided text. All text has at least 1 line | |
1665 | * (even if @text_size is 0). Each '\n' processed is counted as an additional | |
1666 | * line. | |
1667 | */ | |
d397820f | 1668 | static unsigned int count_lines(const char *text, unsigned int text_size) |
b6cf8b3f JO |
1669 | { |
1670 | unsigned int next_size = text_size; | |
1671 | unsigned int line_count = 1; | |
d397820f | 1672 | const char *next = text; |
b6cf8b3f JO |
1673 | |
1674 | while (next_size) { | |
1675 | next = memchr(next, '\n', next_size); | |
1676 | if (!next) | |
1677 | break; | |
1678 | line_count++; | |
1679 | next++; | |
1680 | next_size = text_size - (next - text); | |
1681 | } | |
1682 | ||
1683 | return line_count; | |
1684 | } | |
1685 | ||
1686 | /* | |
1687 | * Given @blk_lpos, copy an expected @len of data into the provided buffer. | |
1688 | * If @line_count is provided, count the number of lines in the data. | |
1689 | * | |
1690 | * This function (used by readers) performs strict validation on the data | |
1691 | * size to possibly detect bugs in the writer code. A WARN_ON_ONCE() is | |
1692 | * triggered if an internal error is detected. | |
1693 | */ | |
1694 | static bool copy_data(struct prb_data_ring *data_ring, | |
1695 | struct prb_data_blk_lpos *blk_lpos, u16 len, char *buf, | |
1696 | unsigned int buf_size, unsigned int *line_count) | |
1697 | { | |
1698 | unsigned int data_size; | |
d397820f | 1699 | const char *data; |
b6cf8b3f JO |
1700 | |
1701 | /* Caller might not want any data. */ | |
1702 | if ((!buf || !buf_size) && !line_count) | |
1703 | return true; | |
1704 | ||
1705 | data = get_data(data_ring, blk_lpos, &data_size); | |
1706 | if (!data) | |
1707 | return false; | |
1708 | ||
1709 | /* | |
1710 | * Actual cannot be less than expected. It can be more than expected | |
1711 | * because of the trailing alignment padding. | |
cfe2790b JO |
1712 | * |
1713 | * Note that invalid @len values can occur because the caller loads | |
1714 | * the value during an allowed data race. | |
b6cf8b3f | 1715 | */ |
cfe2790b | 1716 | if (data_size < (unsigned int)len) |
b6cf8b3f | 1717 | return false; |
b6cf8b3f JO |
1718 | |
1719 | /* Caller interested in the line count? */ | |
1720 | if (line_count) | |
668af87f | 1721 | *line_count = count_lines(data, len); |
b6cf8b3f JO |
1722 | |
1723 | /* Caller interested in the data content? */ | |
1724 | if (!buf || !buf_size) | |
1725 | return true; | |
1726 | ||
1727 | data_size = min_t(u16, buf_size, len); | |
1728 | ||
d397820f | 1729 | memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */ |
b6cf8b3f JO |
1730 | return true; |
1731 | } | |
1732 | ||
1733 | /* | |
1734 | * This is an extended version of desc_read(). It gets a copy of a specified | |
4cfc7258 | 1735 | * descriptor. However, it also verifies that the record is finalized and has |
b6cf8b3f JO |
1736 | * the sequence number @seq. On success, 0 is returned. |
1737 | * | |
1738 | * Error return values: | |
4cfc7258 JO |
1739 | * -EINVAL: A finalized record with sequence number @seq does not exist. |
1740 | * -ENOENT: A finalized record with sequence number @seq exists, but its data | |
b6cf8b3f JO |
1741 | * is not available. This is a valid record, so readers should |
1742 | * continue with the next record. | |
1743 | */ | |
4cfc7258 | 1744 | static int desc_read_finalized_seq(struct prb_desc_ring *desc_ring, |
b6cf8b3f JO |
1745 | unsigned long id, u64 seq, |
1746 | struct prb_desc *desc_out) | |
1747 | { | |
1748 | struct prb_data_blk_lpos *blk_lpos = &desc_out->text_blk_lpos; | |
1749 | enum desc_state d_state; | |
cfe2790b | 1750 | u64 s; |
b6cf8b3f | 1751 | |
cfe2790b | 1752 | d_state = desc_read(desc_ring, id, desc_out, &s, NULL); |
b6cf8b3f JO |
1753 | |
1754 | /* | |
1755 | * An unexpected @id (desc_miss) or @seq mismatch means the record | |
4cfc7258 JO |
1756 | * does not exist. A descriptor in the reserved or committed state |
1757 | * means the record does not yet exist for the reader. | |
b6cf8b3f JO |
1758 | */ |
1759 | if (d_state == desc_miss || | |
1760 | d_state == desc_reserved || | |
4cfc7258 | 1761 | d_state == desc_committed || |
cfe2790b | 1762 | s != seq) { |
b6cf8b3f JO |
1763 | return -EINVAL; |
1764 | } | |
1765 | ||
1766 | /* | |
1767 | * A descriptor in the reusable state may no longer have its data | |
d397820f JO |
1768 | * available; report it as existing but with lost data. Or the record |
1769 | * may actually be a record with lost data. | |
b6cf8b3f JO |
1770 | */ |
1771 | if (d_state == desc_reusable || | |
d397820f | 1772 | (blk_lpos->begin == FAILED_LPOS && blk_lpos->next == FAILED_LPOS)) { |
b6cf8b3f JO |
1773 | return -ENOENT; |
1774 | } | |
1775 | ||
1776 | return 0; | |
1777 | } | |
1778 | ||
1779 | /* | |
1780 | * Copy the ringbuffer data from the record with @seq to the provided | |
1781 | * @r buffer. On success, 0 is returned. | |
1782 | * | |
4cfc7258 | 1783 | * See desc_read_finalized_seq() for error return values. |
b6cf8b3f JO |
1784 | */ |
1785 | static int prb_read(struct printk_ringbuffer *rb, u64 seq, | |
1786 | struct printk_record *r, unsigned int *line_count) | |
1787 | { | |
1788 | struct prb_desc_ring *desc_ring = &rb->desc_ring; | |
cfe2790b | 1789 | struct printk_info *info = to_info(desc_ring, seq); |
b6cf8b3f JO |
1790 | struct prb_desc *rdesc = to_desc(desc_ring, seq); |
1791 | atomic_long_t *state_var = &rdesc->state_var; | |
1792 | struct prb_desc desc; | |
1793 | unsigned long id; | |
1794 | int err; | |
1795 | ||
1796 | /* Extract the ID, used to specify the descriptor to read. */ | |
1797 | id = DESC_ID(atomic_long_read(state_var)); | |
1798 | ||
1799 | /* Get a local copy of the correct descriptor (if available). */ | |
4cfc7258 | 1800 | err = desc_read_finalized_seq(desc_ring, id, seq, &desc); |
b6cf8b3f JO |
1801 | |
1802 | /* | |
1803 | * If @r is NULL, the caller is only interested in the availability | |
1804 | * of the record. | |
1805 | */ | |
1806 | if (err || !r) | |
1807 | return err; | |
1808 | ||
1809 | /* If requested, copy meta data. */ | |
1810 | if (r->info) | |
cfe2790b | 1811 | memcpy(r->info, info, sizeof(*(r->info))); |
b6cf8b3f JO |
1812 | |
1813 | /* Copy text data. If it fails, this is a data-less record. */ | |
cfe2790b | 1814 | if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, info->text_len, |
b6cf8b3f JO |
1815 | r->text_buf, r->text_buf_size, line_count)) { |
1816 | return -ENOENT; | |
1817 | } | |
1818 | ||
4cfc7258 JO |
1819 | /* Ensure the record is still finalized and has the same @seq. */ |
1820 | return desc_read_finalized_seq(desc_ring, id, seq, &desc); | |
b6cf8b3f JO |
1821 | } |
1822 | ||
1823 | /* Get the sequence number of the tail descriptor. */ | |
1824 | static u64 prb_first_seq(struct printk_ringbuffer *rb) | |
1825 | { | |
1826 | struct prb_desc_ring *desc_ring = &rb->desc_ring; | |
1827 | enum desc_state d_state; | |
1828 | struct prb_desc desc; | |
1829 | unsigned long id; | |
cfe2790b | 1830 | u64 seq; |
b6cf8b3f JO |
1831 | |
1832 | for (;;) { | |
1833 | id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */ | |
1834 | ||
cfe2790b | 1835 | d_state = desc_read(desc_ring, id, &desc, &seq, NULL); /* LMM(prb_first_seq:B) */ |
b6cf8b3f JO |
1836 | |
1837 | /* | |
1838 | * This loop will not be infinite because the tail is | |
4cfc7258 | 1839 | * _always_ in the finalized or reusable state. |
b6cf8b3f | 1840 | */ |
4cfc7258 | 1841 | if (d_state == desc_finalized || d_state == desc_reusable) |
b6cf8b3f JO |
1842 | break; |
1843 | ||
1844 | /* | |
1845 | * Guarantee the last state load from desc_read() is before | |
1846 | * reloading @tail_id in order to see a new tail in the case | |
1847 | * that the descriptor has been recycled. This pairs with | |
1848 | * desc_reserve:D. | |
1849 | * | |
1850 | * Memory barrier involvement: | |
1851 | * | |
1852 | * If prb_first_seq:B reads from desc_reserve:F, then | |
1853 | * prb_first_seq:A reads from desc_push_tail:B. | |
1854 | * | |
1855 | * Relies on: | |
1856 | * | |
1857 | * MB from desc_push_tail:B to desc_reserve:F | |
1858 | * matching | |
1859 | * RMB prb_first_seq:B to prb_first_seq:A | |
1860 | */ | |
1861 | smp_rmb(); /* LMM(prb_first_seq:C) */ | |
1862 | } | |
1863 | ||
cfe2790b | 1864 | return seq; |
b6cf8b3f JO |
1865 | } |
1866 | ||
1867 | /* | |
4cfc7258 JO |
1868 | * Non-blocking read of a record. Updates @seq to the last finalized record |
1869 | * (which may have no data available). | |
b6cf8b3f JO |
1870 | * |
1871 | * See the description of prb_read_valid() and prb_read_valid_info() | |
1872 | * for details. | |
1873 | */ | |
1874 | static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, | |
1875 | struct printk_record *r, unsigned int *line_count) | |
1876 | { | |
1877 | u64 tail_seq; | |
1878 | int err; | |
1879 | ||
1880 | while ((err = prb_read(rb, *seq, r, line_count))) { | |
1881 | tail_seq = prb_first_seq(rb); | |
1882 | ||
1883 | if (*seq < tail_seq) { | |
1884 | /* | |
1885 | * Behind the tail. Catch up and try again. This | |
1886 | * can happen for -ENOENT and -EINVAL cases. | |
1887 | */ | |
1888 | *seq = tail_seq; | |
1889 | ||
1890 | } else if (err == -ENOENT) { | |
1891 | /* Record exists, but no data available. Skip. */ | |
1892 | (*seq)++; | |
1893 | ||
1894 | } else { | |
4cfc7258 | 1895 | /* Non-existent/non-finalized record. Must stop. */ |
b6cf8b3f JO |
1896 | return false; |
1897 | } | |
1898 | } | |
1899 | ||
1900 | return true; | |
1901 | } | |
1902 | ||
1903 | /** | |
1904 | * prb_read_valid() - Non-blocking read of a requested record or (if gone) | |
1905 | * the next available record. | |
1906 | * | |
1907 | * @rb: The ringbuffer to read from. | |
1908 | * @seq: The sequence number of the record to read. | |
1909 | * @r: A record data buffer to store the read record to. | |
1910 | * | |
1911 | * This is the public function available to readers to read a record. | |
1912 | * | |
f35efc78 | 1913 | * The reader provides the @info and @text_buf buffers of @r to be |
b6cf8b3f JO |
1914 | * filled in. Any of the buffer pointers can be set to NULL if the reader |
1915 | * is not interested in that data. To ensure proper initialization of @r, | |
1916 | * prb_rec_init_rd() should be used. | |
1917 | * | |
1918 | * Context: Any context. | |
1919 | * Return: true if a record was read, otherwise false. | |
1920 | * | |
1921 | * On success, the reader must check r->info.seq to see which record was | |
1922 | * actually read. This allows the reader to detect dropped records. | |
1923 | * | |
1924 | * Failure means @seq refers to a not yet written record. | |
1925 | */ | |
1926 | bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, | |
1927 | struct printk_record *r) | |
1928 | { | |
1929 | return _prb_read_valid(rb, &seq, r, NULL); | |
1930 | } | |
1931 | ||
1932 | /** | |
1933 | * prb_read_valid_info() - Non-blocking read of meta data for a requested | |
1934 | * record or (if gone) the next available record. | |
1935 | * | |
1936 | * @rb: The ringbuffer to read from. | |
1937 | * @seq: The sequence number of the record to read. | |
1938 | * @info: A buffer to store the read record meta data to. | |
1939 | * @line_count: A buffer to store the number of lines in the record text. | |
1940 | * | |
1941 | * This is the public function available to readers to read only the | |
1942 | * meta data of a record. | |
1943 | * | |
1944 | * The reader provides the @info, @line_count buffers to be filled in. | |
1945 | * Either of the buffer pointers can be set to NULL if the reader is not | |
1946 | * interested in that data. | |
1947 | * | |
1948 | * Context: Any context. | |
1949 | * Return: true if a record's meta data was read, otherwise false. | |
1950 | * | |
1951 | * On success, the reader must check info->seq to see which record meta data | |
1952 | * was actually read. This allows the reader to detect dropped records. | |
1953 | * | |
1954 | * Failure means @seq refers to a not yet written record. | |
1955 | */ | |
1956 | bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, | |
1957 | struct printk_info *info, unsigned int *line_count) | |
1958 | { | |
1959 | struct printk_record r; | |
1960 | ||
f35efc78 | 1961 | prb_rec_init_rd(&r, info, NULL, 0); |
b6cf8b3f JO |
1962 | |
1963 | return _prb_read_valid(rb, &seq, &r, line_count); | |
1964 | } | |
1965 | ||
1966 | /** | |
1967 | * prb_first_valid_seq() - Get the sequence number of the oldest available | |
1968 | * record. | |
1969 | * | |
1970 | * @rb: The ringbuffer to get the sequence number from. | |
1971 | * | |
1972 | * This is the public function available to readers to see what the | |
1973 | * first/oldest valid sequence number is. | |
1974 | * | |
1975 | * This provides readers a starting point to begin iterating the ringbuffer. | |
1976 | * | |
1977 | * Context: Any context. | |
1978 | * Return: The sequence number of the first/oldest record or, if the | |
1979 | * ringbuffer is empty, 0 is returned. | |
1980 | */ | |
1981 | u64 prb_first_valid_seq(struct printk_ringbuffer *rb) | |
1982 | { | |
1983 | u64 seq = 0; | |
1984 | ||
1985 | if (!_prb_read_valid(rb, &seq, NULL, NULL)) | |
1986 | return 0; | |
1987 | ||
1988 | return seq; | |
1989 | } | |
1990 | ||
1991 | /** | |
1992 | * prb_next_seq() - Get the sequence number after the last available record. | |
1993 | * | |
1994 | * @rb: The ringbuffer to get the sequence number from. | |
1995 | * | |
1996 | * This is the public function available to readers to see what the next | |
1997 | * newest sequence number available to readers will be. | |
1998 | * | |
1999 | * This provides readers a sequence number to jump to if all currently | |
2000 | * available records should be skipped. | |
2001 | * | |
2002 | * Context: Any context. | |
2003 | * Return: The sequence number of the next newest (not yet available) record | |
2004 | * for readers. | |
2005 | */ | |
2006 | u64 prb_next_seq(struct printk_ringbuffer *rb) | |
2007 | { | |
2008 | u64 seq = 0; | |
2009 | ||
2010 | /* Search forward from the oldest descriptor. */ | |
2011 | while (_prb_read_valid(rb, &seq, NULL, NULL)) | |
2012 | seq++; | |
2013 | ||
2014 | return seq; | |
2015 | } | |
2016 | ||
2017 | /** | |
2018 | * prb_init() - Initialize a ringbuffer to use provided external buffers. | |
2019 | * | |
2020 | * @rb: The ringbuffer to initialize. | |
2021 | * @text_buf: The data buffer for text data. | |
2022 | * @textbits: The size of @text_buf as a power-of-2 value. | |
b6cf8b3f JO |
2023 | * @descs: The descriptor buffer for ringbuffer records. |
2024 | * @descbits: The count of @descs items as a power-of-2 value. | |
cfe2790b | 2025 | * @infos: The printk_info buffer for ringbuffer records. |
b6cf8b3f JO |
2026 | * |
2027 | * This is the public function available to writers to setup a ringbuffer | |
2028 | * during runtime using provided buffers. | |
2029 | * | |
2030 | * This must match the initialization of DEFINE_PRINTKRB(). | |
2031 | * | |
2032 | * Context: Any context. | |
2033 | */ | |
2034 | void prb_init(struct printk_ringbuffer *rb, | |
2035 | char *text_buf, unsigned int textbits, | |
cfe2790b JO |
2036 | struct prb_desc *descs, unsigned int descbits, |
2037 | struct printk_info *infos) | |
b6cf8b3f JO |
2038 | { |
2039 | memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0])); | |
cfe2790b | 2040 | memset(infos, 0, _DESCS_COUNT(descbits) * sizeof(infos[0])); |
b6cf8b3f JO |
2041 | |
2042 | rb->desc_ring.count_bits = descbits; | |
2043 | rb->desc_ring.descs = descs; | |
cfe2790b | 2044 | rb->desc_ring.infos = infos; |
b6cf8b3f JO |
2045 | atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits)); |
2046 | atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits)); | |
2047 | ||
2048 | rb->text_data_ring.size_bits = textbits; | |
2049 | rb->text_data_ring.data = text_buf; | |
2050 | atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits)); | |
2051 | atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits)); | |
2052 | ||
b6cf8b3f JO |
2053 | atomic_long_set(&rb->fail, 0); |
2054 | ||
b6cf8b3f | 2055 | atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits)); |
d397820f JO |
2056 | descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = FAILED_LPOS; |
2057 | descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = FAILED_LPOS; | |
cfe2790b JO |
2058 | |
2059 | infos[0].seq = -(u64)_DESCS_COUNT(descbits); | |
2060 | infos[_DESCS_COUNT(descbits) - 1].seq = 0; | |
b6cf8b3f JO |
2061 | } |
2062 | ||
2063 | /** | |
2064 | * prb_record_text_space() - Query the full actual used ringbuffer space for | |
2065 | * the text data of a reserved entry. | |
2066 | * | |
2067 | * @e: The successfully reserved entry to query. | |
2068 | * | |
2069 | * This is the public function available to writers to see how much actual | |
2070 | * space is used in the ringbuffer to store the text data of the specified | |
2071 | * entry. | |
2072 | * | |
2073 | * This function is only valid if @e has been successfully reserved using | |
2074 | * prb_reserve(). | |
2075 | * | |
2076 | * Context: Any context. | |
2077 | * Return: The size in bytes used by the text data of the associated record. | |
2078 | */ | |
2079 | unsigned int prb_record_text_space(struct prb_reserved_entry *e) | |
2080 | { | |
2081 | return e->text_space; | |
2082 | } |