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1/* SPDX-License-Identifier: GPL-2.0 */
2
3#ifndef _KERNEL_PRINTK_RINGBUFFER_H
4#define _KERNEL_PRINTK_RINGBUFFER_H
5
6#include <linux/atomic.h>
7#include <linux/dev_printk.h>
8
9/*
10 * Meta information about each stored message.
11 *
12 * All fields are set by the printk code except for @seq, which is
13 * set by the ringbuffer code.
14 */
15struct printk_info {
16 u64 seq; /* sequence number */
17 u64 ts_nsec; /* timestamp in nanoseconds */
18 u16 text_len; /* length of text message */
19 u8 facility; /* syslog facility */
20 u8 flags:5; /* internal record flags */
21 u8 level:3; /* syslog level */
22 u32 caller_id; /* thread id or processor id */
23
24 struct dev_printk_info dev_info;
25};
26
27/*
28 * A structure providing the buffers, used by writers and readers.
29 *
30 * Writers:
31 * Using prb_rec_init_wr(), a writer sets @text_buf_size before calling
32 * prb_reserve(). On success, prb_reserve() sets @info and @text_buf to
33 * buffers reserved for that writer.
34 *
35 * Readers:
36 * Using prb_rec_init_rd(), a reader sets all fields before calling
37 * prb_read_valid(). Note that the reader provides the @info and @text_buf,
38 * buffers. On success, the struct pointed to by @info will be filled and
39 * the char array pointed to by @text_buf will be filled with text data.
40 */
41struct printk_record {
42 struct printk_info *info;
43 char *text_buf;
44 unsigned int text_buf_size;
45};
46
47/* Specifies the logical position and span of a data block. */
48struct prb_data_blk_lpos {
49 unsigned long begin;
50 unsigned long next;
51};
52
53/*
54 * A descriptor: the complete meta-data for a record.
55 *
56 * @state_var: A bitwise combination of descriptor ID and descriptor state.
57 */
58struct prb_desc {
59 atomic_long_t state_var;
60 struct prb_data_blk_lpos text_blk_lpos;
61};
62
63/* A ringbuffer of "ID + data" elements. */
64struct prb_data_ring {
65 unsigned int size_bits;
66 char *data;
67 atomic_long_t head_lpos;
68 atomic_long_t tail_lpos;
69};
70
71/* A ringbuffer of "struct prb_desc" elements. */
72struct prb_desc_ring {
73 unsigned int count_bits;
74 struct prb_desc *descs;
75 struct printk_info *infos;
76 atomic_long_t head_id;
77 atomic_long_t tail_id;
78 atomic_long_t last_finalized_id;
79};
80
81/*
82 * The high level structure representing the printk ringbuffer.
83 *
84 * @fail: Count of failed prb_reserve() calls where not even a data-less
85 * record was created.
86 */
87struct printk_ringbuffer {
88 struct prb_desc_ring desc_ring;
89 struct prb_data_ring text_data_ring;
90 atomic_long_t fail;
91};
92
93/*
94 * Used by writers as a reserve/commit handle.
95 *
96 * @rb: Ringbuffer where the entry is reserved.
97 * @irqflags: Saved irq flags to restore on entry commit.
98 * @id: ID of the reserved descriptor.
99 * @text_space: Total occupied buffer space in the text data ring, including
100 * ID, alignment padding, and wrapping data blocks.
101 *
102 * This structure is an opaque handle for writers. Its contents are only
103 * to be used by the ringbuffer implementation.
104 */
105struct prb_reserved_entry {
106 struct printk_ringbuffer *rb;
107 unsigned long irqflags;
108 unsigned long id;
109 unsigned int text_space;
110};
111
112/* The possible responses of a descriptor state-query. */
113enum desc_state {
114 desc_miss = -1, /* ID mismatch (pseudo state) */
115 desc_reserved = 0x0, /* reserved, in use by writer */
116 desc_committed = 0x1, /* committed by writer, could get reopened */
117 desc_finalized = 0x2, /* committed, no further modification allowed */
118 desc_reusable = 0x3, /* free, not yet used by any writer */
119};
120
121#define _DATA_SIZE(sz_bits) (1UL << (sz_bits))
122#define _DESCS_COUNT(ct_bits) (1U << (ct_bits))
123#define DESC_SV_BITS (sizeof(unsigned long) * 8)
124#define DESC_FLAGS_SHIFT (DESC_SV_BITS - 2)
125#define DESC_FLAGS_MASK (3UL << DESC_FLAGS_SHIFT)
126#define DESC_STATE(sv) (3UL & (sv >> DESC_FLAGS_SHIFT))
127#define DESC_SV(id, state) (((unsigned long)state << DESC_FLAGS_SHIFT) | id)
128#define DESC_ID_MASK (~DESC_FLAGS_MASK)
129#define DESC_ID(sv) ((sv) & DESC_ID_MASK)
130#define FAILED_LPOS 0x1
131#define NO_LPOS 0x3
132
133#define FAILED_BLK_LPOS \
134{ \
135 .begin = FAILED_LPOS, \
136 .next = FAILED_LPOS, \
137}
138
139/*
140 * Descriptor Bootstrap
141 *
142 * The descriptor array is minimally initialized to allow immediate usage
143 * by readers and writers. The requirements that the descriptor array
144 * initialization must satisfy:
145 *
146 * Req1
147 * The tail must point to an existing (committed or reusable) descriptor.
148 * This is required by the implementation of prb_first_seq().
149 *
150 * Req2
151 * Readers must see that the ringbuffer is initially empty.
152 *
153 * Req3
154 * The first record reserved by a writer is assigned sequence number 0.
155 *
156 * To satisfy Req1, the tail initially points to a descriptor that is
157 * minimally initialized (having no data block, i.e. data-less with the
158 * data block's lpos @begin and @next values set to FAILED_LPOS).
159 *
160 * To satisfy Req2, the initial tail descriptor is initialized to the
161 * reusable state. Readers recognize reusable descriptors as existing
162 * records, but skip over them.
163 *
164 * To satisfy Req3, the last descriptor in the array is used as the initial
165 * head (and tail) descriptor. This allows the first record reserved by a
166 * writer (head + 1) to be the first descriptor in the array. (Only the first
167 * descriptor in the array could have a valid sequence number of 0.)
168 *
169 * The first time a descriptor is reserved, it is assigned a sequence number
170 * with the value of the array index. A "first time reserved" descriptor can
171 * be recognized because it has a sequence number of 0 but does not have an
172 * index of 0. (Only the first descriptor in the array could have a valid
173 * sequence number of 0.) After the first reservation, all future reservations
174 * (recycling) simply involve incrementing the sequence number by the array
175 * count.
176 *
177 * Hack #1
178 * Only the first descriptor in the array is allowed to have the sequence
179 * number 0. In this case it is not possible to recognize if it is being
180 * reserved the first time (set to index value) or has been reserved
181 * previously (increment by the array count). This is handled by _always_
182 * incrementing the sequence number by the array count when reserving the
183 * first descriptor in the array. In order to satisfy Req3, the sequence
184 * number of the first descriptor in the array is initialized to minus
185 * the array count. Then, upon the first reservation, it is incremented
186 * to 0, thus satisfying Req3.
187 *
188 * Hack #2
189 * prb_first_seq() can be called at any time by readers to retrieve the
190 * sequence number of the tail descriptor. However, due to Req2 and Req3,
191 * initially there are no records to report the sequence number of
192 * (sequence numbers are u64 and there is nothing less than 0). To handle
193 * this, the sequence number of the initial tail descriptor is initialized
194 * to 0. Technically this is incorrect, because there is no record with
195 * sequence number 0 (yet) and the tail descriptor is not the first
196 * descriptor in the array. But it allows prb_read_valid() to correctly
197 * report the existence of a record for _any_ given sequence number at all
198 * times. Bootstrapping is complete when the tail is pushed the first
199 * time, thus finally pointing to the first descriptor reserved by a
200 * writer, which has the assigned sequence number 0.
201 */
202
203/*
204 * Initiating Logical Value Overflows
205 *
206 * Both logical position (lpos) and ID values can be mapped to array indexes
207 * but may experience overflows during the lifetime of the system. To ensure
208 * that printk_ringbuffer can handle the overflows for these types, initial
209 * values are chosen that map to the correct initial array indexes, but will
210 * result in overflows soon.
211 *
212 * BLK0_LPOS
213 * The initial @head_lpos and @tail_lpos for data rings. It is at index
214 * 0 and the lpos value is such that it will overflow on the first wrap.
215 *
216 * DESC0_ID
217 * The initial @head_id and @tail_id for the desc ring. It is at the last
218 * index of the descriptor array (see Req3 above) and the ID value is such
219 * that it will overflow on the second wrap.
220 */
221#define BLK0_LPOS(sz_bits) (-(_DATA_SIZE(sz_bits)))
222#define DESC0_ID(ct_bits) DESC_ID(-(_DESCS_COUNT(ct_bits) + 1))
223#define DESC0_SV(ct_bits) DESC_SV(DESC0_ID(ct_bits), desc_reusable)
224
225/*
226 * Define a ringbuffer with an external text data buffer. The same as
227 * DEFINE_PRINTKRB() but requires specifying an external buffer for the
228 * text data.
229 *
230 * Note: The specified external buffer must be of the size:
231 * 2 ^ (descbits + avgtextbits)
232 */
233#define _DEFINE_PRINTKRB(name, descbits, avgtextbits, text_buf) \
234static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \
235 /* the initial head and tail */ \
236 [_DESCS_COUNT(descbits) - 1] = { \
237 /* reusable */ \
238 .state_var = ATOMIC_INIT(DESC0_SV(descbits)), \
239 /* no associated data block */ \
240 .text_blk_lpos = FAILED_BLK_LPOS, \
241 }, \
242}; \
243static struct printk_info _##name##_infos[_DESCS_COUNT(descbits)] = { \
244 /* this will be the first record reserved by a writer */ \
245 [0] = { \
246 /* will be incremented to 0 on the first reservation */ \
247 .seq = -(u64)_DESCS_COUNT(descbits), \
248 }, \
249 /* the initial head and tail */ \
250 [_DESCS_COUNT(descbits) - 1] = { \
251 /* reports the first seq value during the bootstrap phase */ \
252 .seq = 0, \
253 }, \
254}; \
255static struct printk_ringbuffer name = { \
256 .desc_ring = { \
257 .count_bits = descbits, \
258 .descs = &_##name##_descs[0], \
259 .infos = &_##name##_infos[0], \
260 .head_id = ATOMIC_INIT(DESC0_ID(descbits)), \
261 .tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \
262 .last_finalized_id = ATOMIC_INIT(DESC0_ID(descbits)), \
263 }, \
264 .text_data_ring = { \
265 .size_bits = (avgtextbits) + (descbits), \
266 .data = text_buf, \
267 .head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \
268 .tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \
269 }, \
270 .fail = ATOMIC_LONG_INIT(0), \
271}
272
273/**
274 * DEFINE_PRINTKRB() - Define a ringbuffer.
275 *
276 * @name: The name of the ringbuffer variable.
277 * @descbits: The number of descriptors as a power-of-2 value.
278 * @avgtextbits: The average text data size per record as a power-of-2 value.
279 *
280 * This is a macro for defining a ringbuffer and all internal structures
281 * such that it is ready for immediate use. See _DEFINE_PRINTKRB() for a
282 * variant where the text data buffer can be specified externally.
283 */
284#define DEFINE_PRINTKRB(name, descbits, avgtextbits) \
285static char _##name##_text[1U << ((avgtextbits) + (descbits))] \
286 __aligned(__alignof__(unsigned long)); \
287_DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0])
288
289/* Writer Interface */
290
291/**
292 * prb_rec_init_wr() - Initialize a buffer for writing records.
293 *
294 * @r: The record to initialize.
295 * @text_buf_size: The needed text buffer size.
296 */
297static inline void prb_rec_init_wr(struct printk_record *r,
298 unsigned int text_buf_size)
299{
300 r->info = NULL;
301 r->text_buf = NULL;
302 r->text_buf_size = text_buf_size;
303}
304
305bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
306 struct printk_record *r);
307bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,
308 struct printk_record *r, u32 caller_id, unsigned int max_size);
309void prb_commit(struct prb_reserved_entry *e);
310void prb_final_commit(struct prb_reserved_entry *e);
311
312void prb_init(struct printk_ringbuffer *rb,
313 char *text_buf, unsigned int text_buf_size,
314 struct prb_desc *descs, unsigned int descs_count_bits,
315 struct printk_info *infos);
316unsigned int prb_record_text_space(struct prb_reserved_entry *e);
317
318/* Reader Interface */
319
320/**
321 * prb_rec_init_rd() - Initialize a buffer for reading records.
322 *
323 * @r: The record to initialize.
324 * @info: A buffer to store record meta-data.
325 * @text_buf: A buffer to store text data.
326 * @text_buf_size: The size of @text_buf.
327 *
328 * Initialize all the fields that a reader is interested in. All arguments
329 * (except @r) are optional. Only record data for arguments that are
330 * non-NULL or non-zero will be read.
331 */
332static inline void prb_rec_init_rd(struct printk_record *r,
333 struct printk_info *info,
334 char *text_buf, unsigned int text_buf_size)
335{
336 r->info = info;
337 r->text_buf = text_buf;
338 r->text_buf_size = text_buf_size;
339}
340
341/**
342 * prb_for_each_record() - Iterate over the records of a ringbuffer.
343 *
344 * @from: The sequence number to begin with.
345 * @rb: The ringbuffer to iterate over.
346 * @s: A u64 to store the sequence number on each iteration.
347 * @r: A printk_record to store the record on each iteration.
348 *
349 * This is a macro for conveniently iterating over a ringbuffer.
350 * Note that @s may not be the sequence number of the record on each
351 * iteration. For the sequence number, @r->info->seq should be checked.
352 *
353 * Context: Any context.
354 */
355#define prb_for_each_record(from, rb, s, r) \
356for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1)
357
358/**
359 * prb_for_each_info() - Iterate over the meta data of a ringbuffer.
360 *
361 * @from: The sequence number to begin with.
362 * @rb: The ringbuffer to iterate over.
363 * @s: A u64 to store the sequence number on each iteration.
364 * @i: A printk_info to store the record meta data on each iteration.
365 * @lc: An unsigned int to store the text line count of each record.
366 *
367 * This is a macro for conveniently iterating over a ringbuffer.
368 * Note that @s may not be the sequence number of the record on each
369 * iteration. For the sequence number, @r->info->seq should be checked.
370 *
371 * Context: Any context.
372 */
373#define prb_for_each_info(from, rb, s, i, lc) \
374for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1)
375
376bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
377 struct printk_record *r);
378bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
379 struct printk_info *info, unsigned int *line_count);
380
381u64 prb_first_valid_seq(struct printk_ringbuffer *rb);
382u64 prb_next_seq(struct printk_ringbuffer *rb);
383
384#endif /* _KERNEL_PRINTK_RINGBUFFER_H */