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_seq; 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) 130 131/* 132 * Special data block logical position values (for fields of 133 * @prb_desc.text_blk_lpos). 134 * 135 * - Bit0 is used to identify if the record has no data block. (Implemented in 136 * the LPOS_DATALESS() macro.) 137 * 138 * - Bit1 specifies the reason for not having a data block. 139 * 140 * These special values could never be real lpos values because of the 141 * meta data and alignment padding of data blocks. (See to_blk_size() for 142 * details.) 143 */ 144#define FAILED_LPOS 0x1 145#define EMPTY_LINE_LPOS 0x3 146 147#define FAILED_BLK_LPOS \ 148{ \ 149 .begin = FAILED_LPOS, \ 150 .next = FAILED_LPOS, \ 151} 152 153/* 154 * Descriptor Bootstrap 155 * 156 * The descriptor array is minimally initialized to allow immediate usage 157 * by readers and writers. The requirements that the descriptor array 158 * initialization must satisfy: 159 * 160 * Req1 161 * The tail must point to an existing (committed or reusable) descriptor. 162 * This is required by the implementation of prb_first_seq(). 163 * 164 * Req2 165 * Readers must see that the ringbuffer is initially empty. 166 * 167 * Req3 168 * The first record reserved by a writer is assigned sequence number 0. 169 * 170 * To satisfy Req1, the tail initially points to a descriptor that is 171 * minimally initialized (having no data block, i.e. data-less with the 172 * data block's lpos @begin and @next values set to FAILED_LPOS). 173 * 174 * To satisfy Req2, the initial tail descriptor is initialized to the 175 * reusable state. Readers recognize reusable descriptors as existing 176 * records, but skip over them. 177 * 178 * To satisfy Req3, the last descriptor in the array is used as the initial 179 * head (and tail) descriptor. This allows the first record reserved by a 180 * writer (head + 1) to be the first descriptor in the array. (Only the first 181 * descriptor in the array could have a valid sequence number of 0.) 182 * 183 * The first time a descriptor is reserved, it is assigned a sequence number 184 * with the value of the array index. A "first time reserved" descriptor can 185 * be recognized because it has a sequence number of 0 but does not have an 186 * index of 0. (Only the first descriptor in the array could have a valid 187 * sequence number of 0.) After the first reservation, all future reservations 188 * (recycling) simply involve incrementing the sequence number by the array 189 * count. 190 * 191 * Hack #1 192 * Only the first descriptor in the array is allowed to have the sequence 193 * number 0. In this case it is not possible to recognize if it is being 194 * reserved the first time (set to index value) or has been reserved 195 * previously (increment by the array count). This is handled by _always_ 196 * incrementing the sequence number by the array count when reserving the 197 * first descriptor in the array. In order to satisfy Req3, the sequence 198 * number of the first descriptor in the array is initialized to minus 199 * the array count. Then, upon the first reservation, it is incremented 200 * to 0, thus satisfying Req3. 201 * 202 * Hack #2 203 * prb_first_seq() can be called at any time by readers to retrieve the 204 * sequence number of the tail descriptor. However, due to Req2 and Req3, 205 * initially there are no records to report the sequence number of 206 * (sequence numbers are u64 and there is nothing less than 0). To handle 207 * this, the sequence number of the initial tail descriptor is initialized 208 * to 0. Technically this is incorrect, because there is no record with 209 * sequence number 0 (yet) and the tail descriptor is not the first 210 * descriptor in the array. But it allows prb_read_valid() to correctly 211 * report the existence of a record for _any_ given sequence number at all 212 * times. Bootstrapping is complete when the tail is pushed the first 213 * time, thus finally pointing to the first descriptor reserved by a 214 * writer, which has the assigned sequence number 0. 215 */ 216 217/* 218 * Initiating Logical Value Overflows 219 * 220 * Both logical position (lpos) and ID values can be mapped to array indexes 221 * but may experience overflows during the lifetime of the system. To ensure 222 * that printk_ringbuffer can handle the overflows for these types, initial 223 * values are chosen that map to the correct initial array indexes, but will 224 * result in overflows soon. 225 * 226 * BLK0_LPOS 227 * The initial @head_lpos and @tail_lpos for data rings. It is at index 228 * 0 and the lpos value is such that it will overflow on the first wrap. 229 * 230 * DESC0_ID 231 * The initial @head_id and @tail_id for the desc ring. It is at the last 232 * index of the descriptor array (see Req3 above) and the ID value is such 233 * that it will overflow on the second wrap. 234 */ 235#define BLK0_LPOS(sz_bits) (-(_DATA_SIZE(sz_bits))) 236#define DESC0_ID(ct_bits) DESC_ID(-(_DESCS_COUNT(ct_bits) + 1)) 237#define DESC0_SV(ct_bits) DESC_SV(DESC0_ID(ct_bits), desc_reusable) 238 239/* 240 * Define a ringbuffer with an external text data buffer. The same as 241 * DEFINE_PRINTKRB() but requires specifying an external buffer for the 242 * text data. 243 * 244 * Note: The specified external buffer must be of the size: 245 * 2 ^ (descbits + avgtextbits) 246 */ 247#define _DEFINE_PRINTKRB(name, descbits, avgtextbits, text_buf) \ 248static struct prb_desc _##name##_descs[_DESCS_COUNT(descbits)] = { \ 249 /* the initial head and tail */ \ 250 [_DESCS_COUNT(descbits) - 1] = { \ 251 /* reusable */ \ 252 .state_var = ATOMIC_INIT(DESC0_SV(descbits)), \ 253 /* no associated data block */ \ 254 .text_blk_lpos = FAILED_BLK_LPOS, \ 255 }, \ 256}; \ 257static struct printk_info _##name##_infos[_DESCS_COUNT(descbits)] = { \ 258 /* this will be the first record reserved by a writer */ \ 259 [0] = { \ 260 /* will be incremented to 0 on the first reservation */ \ 261 .seq = -(u64)_DESCS_COUNT(descbits), \ 262 }, \ 263 /* the initial head and tail */ \ 264 [_DESCS_COUNT(descbits) - 1] = { \ 265 /* reports the first seq value during the bootstrap phase */ \ 266 .seq = 0, \ 267 }, \ 268}; \ 269static struct printk_ringbuffer name = { \ 270 .desc_ring = { \ 271 .count_bits = descbits, \ 272 .descs = &_##name##_descs[0], \ 273 .infos = &_##name##_infos[0], \ 274 .head_id = ATOMIC_INIT(DESC0_ID(descbits)), \ 275 .tail_id = ATOMIC_INIT(DESC0_ID(descbits)), \ 276 .last_finalized_seq = ATOMIC_INIT(0), \ 277 }, \ 278 .text_data_ring = { \ 279 .size_bits = (avgtextbits) + (descbits), \ 280 .data = text_buf, \ 281 .head_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ 282 .tail_lpos = ATOMIC_LONG_INIT(BLK0_LPOS((avgtextbits) + (descbits))), \ 283 }, \ 284 .fail = ATOMIC_LONG_INIT(0), \ 285} 286 287/** 288 * DEFINE_PRINTKRB() - Define a ringbuffer. 289 * 290 * @name: The name of the ringbuffer variable. 291 * @descbits: The number of descriptors as a power-of-2 value. 292 * @avgtextbits: The average text data size per record as a power-of-2 value. 293 * 294 * This is a macro for defining a ringbuffer and all internal structures 295 * such that it is ready for immediate use. See _DEFINE_PRINTKRB() for a 296 * variant where the text data buffer can be specified externally. 297 */ 298#define DEFINE_PRINTKRB(name, descbits, avgtextbits) \ 299static char _##name##_text[1U << ((avgtextbits) + (descbits))] \ 300 __aligned(__alignof__(unsigned long)); \ 301_DEFINE_PRINTKRB(name, descbits, avgtextbits, &_##name##_text[0]) 302 303/* Writer Interface */ 304 305/** 306 * prb_rec_init_wr() - Initialize a buffer for writing records. 307 * 308 * @r: The record to initialize. 309 * @text_buf_size: The needed text buffer size. 310 */ 311static inline void prb_rec_init_wr(struct printk_record *r, 312 unsigned int text_buf_size) 313{ 314 r->info = NULL; 315 r->text_buf = NULL; 316 r->text_buf_size = text_buf_size; 317} 318 319bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, 320 struct printk_record *r); 321bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, 322 struct printk_record *r, u32 caller_id, unsigned int max_size); 323void prb_commit(struct prb_reserved_entry *e); 324void prb_final_commit(struct prb_reserved_entry *e); 325 326void prb_init(struct printk_ringbuffer *rb, 327 char *text_buf, unsigned int text_buf_size, 328 struct prb_desc *descs, unsigned int descs_count_bits, 329 struct printk_info *infos); 330unsigned int prb_record_text_space(struct prb_reserved_entry *e); 331 332/* Reader Interface */ 333 334/** 335 * prb_rec_init_rd() - Initialize a buffer for reading records. 336 * 337 * @r: The record to initialize. 338 * @info: A buffer to store record meta-data. 339 * @text_buf: A buffer to store text data. 340 * @text_buf_size: The size of @text_buf. 341 * 342 * Initialize all the fields that a reader is interested in. All arguments 343 * (except @r) are optional. Only record data for arguments that are 344 * non-NULL or non-zero will be read. 345 */ 346static inline void prb_rec_init_rd(struct printk_record *r, 347 struct printk_info *info, 348 char *text_buf, unsigned int text_buf_size) 349{ 350 r->info = info; 351 r->text_buf = text_buf; 352 r->text_buf_size = text_buf_size; 353} 354 355/** 356 * prb_for_each_record() - Iterate over the records of a ringbuffer. 357 * 358 * @from: The sequence number to begin with. 359 * @rb: The ringbuffer to iterate over. 360 * @s: A u64 to store the sequence number on each iteration. 361 * @r: A printk_record to store the record on each iteration. 362 * 363 * This is a macro for conveniently iterating over a ringbuffer. 364 * Note that @s may not be the sequence number of the record on each 365 * iteration. For the sequence number, @r->info->seq should be checked. 366 * 367 * Context: Any context. 368 */ 369#define prb_for_each_record(from, rb, s, r) \ 370for ((s) = from; prb_read_valid(rb, s, r); (s) = (r)->info->seq + 1) 371 372/** 373 * prb_for_each_info() - Iterate over the meta data of a ringbuffer. 374 * 375 * @from: The sequence number to begin with. 376 * @rb: The ringbuffer to iterate over. 377 * @s: A u64 to store the sequence number on each iteration. 378 * @i: A printk_info to store the record meta data on each iteration. 379 * @lc: An unsigned int to store the text line count of each record. 380 * 381 * This is a macro for conveniently iterating over a ringbuffer. 382 * Note that @s may not be the sequence number of the record on each 383 * iteration. For the sequence number, @r->info->seq should be checked. 384 * 385 * Context: Any context. 386 */ 387#define prb_for_each_info(from, rb, s, i, lc) \ 388for ((s) = from; prb_read_valid_info(rb, s, i, lc); (s) = (i)->seq + 1) 389 390bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, 391 struct printk_record *r); 392bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, 393 struct printk_info *info, unsigned int *line_count); 394 395u64 prb_first_seq(struct printk_ringbuffer *rb); 396u64 prb_first_valid_seq(struct printk_ringbuffer *rb); 397u64 prb_next_seq(struct printk_ringbuffer *rb); 398u64 prb_next_reserve_seq(struct printk_ringbuffer *rb); 399 400#ifdef CONFIG_64BIT 401 402#define __u64seq_to_ulseq(u64seq) (u64seq) 403#define __ulseq_to_u64seq(rb, ulseq) (ulseq) 404 405#else /* CONFIG_64BIT */ 406 407#define __u64seq_to_ulseq(u64seq) ((u32)u64seq) 408 409static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq) 410{ 411 u64 rb_first_seq = prb_first_seq(rb); 412 u64 seq; 413 414 /* 415 * The provided sequence is only the lower 32 bits of the ringbuffer 416 * sequence. It needs to be expanded to 64bit. Get the first sequence 417 * number from the ringbuffer and fold it. 418 * 419 * Having a 32bit representation in the console is sufficient. 420 * If a console ever gets more than 2^31 records behind 421 * the ringbuffer then this is the least of the problems. 422 * 423 * Also the access to the ring buffer is always safe. 424 */ 425 seq = rb_first_seq - (s32)((u32)rb_first_seq - ulseq); 426 427 return seq; 428} 429 430#endif /* CONFIG_64BIT */ 431 432#endif /* _KERNEL_PRINTK_RINGBUFFER_H */ 433