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