1 /* -*- mode: c; c-basic-offset: 8; -*- 2 * vim: noexpandtab sw=8 ts=8 sts=0: 3 * 4 * blockcheck.c 5 * 6 * Checksum and ECC codes for the OCFS2 userspace library. 7 * 8 * Copyright (C) 2006, 2008 Oracle. All rights reserved. 9 * 10 * This program is free software; you can redistribute it and/or 11 * modify it under the terms of the GNU General Public 12 * License, version 2, as published by the Free Software Foundation. 13 * 14 * This program is distributed in the hope that it will be useful, 15 * but WITHOUT ANY WARRANTY; without even the implied warranty of 16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 17 * General Public License for more details. 18 */ 19 20 #include <linux/kernel.h> 21 #include <linux/types.h> 22 #include <linux/crc32.h> 23 #include <linux/buffer_head.h> 24 #include <linux/bitops.h> 25 #include <asm/byteorder.h> 26 27 #include <cluster/masklog.h> 28 29 #include "ocfs2.h" 30 31 #include "blockcheck.h" 32 33 34 /* 35 * We use the following conventions: 36 * 37 * d = # data bits 38 * p = # parity bits 39 * c = # total code bits (d + p) 40 */ 41 42 43 /* 44 * Calculate the bit offset in the hamming code buffer based on the bit's 45 * offset in the data buffer. Since the hamming code reserves all 46 * power-of-two bits for parity, the data bit number and the code bit 47 * number are offest by all the parity bits beforehand. 48 * 49 * Recall that bit numbers in hamming code are 1-based. This function 50 * takes the 0-based data bit from the caller. 51 * 52 * An example. Take bit 1 of the data buffer. 1 is a power of two (2^0), 53 * so it's a parity bit. 2 is a power of two (2^1), so it's a parity bit. 54 * 3 is not a power of two. So bit 1 of the data buffer ends up as bit 3 55 * in the code buffer. 56 * 57 * The caller can pass in *p if it wants to keep track of the most recent 58 * number of parity bits added. This allows the function to start the 59 * calculation at the last place. 60 */ 61 static unsigned int calc_code_bit(unsigned int i, unsigned int *p_cache) 62 { 63 unsigned int b, p = 0; 64 65 /* 66 * Data bits are 0-based, but we're talking code bits, which 67 * are 1-based. 68 */ 69 b = i + 1; 70 71 /* Use the cache if it is there */ 72 if (p_cache) 73 p = *p_cache; 74 b += p; 75 76 /* 77 * For every power of two below our bit number, bump our bit. 78 * 79 * We compare with (b + 1) because we have to compare with what b 80 * would be _if_ it were bumped up by the parity bit. Capice? 81 * 82 * p is set above. 83 */ 84 for (; (1 << p) < (b + 1); p++) 85 b++; 86 87 if (p_cache) 88 *p_cache = p; 89 90 return b; 91 } 92 93 /* 94 * This is the low level encoder function. It can be called across 95 * multiple hunks just like the crc32 code. 'd' is the number of bits 96 * _in_this_hunk_. nr is the bit offset of this hunk. So, if you had 97 * two 512B buffers, you would do it like so: 98 * 99 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0); 100 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8); 101 * 102 * If you just have one buffer, use ocfs2_hamming_encode_block(). 103 */ 104 u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr) 105 { 106 unsigned int i, b, p = 0; 107 108 BUG_ON(!d); 109 110 /* 111 * b is the hamming code bit number. Hamming code specifies a 112 * 1-based array, but C uses 0-based. So 'i' is for C, and 'b' is 113 * for the algorithm. 114 * 115 * The i++ in the for loop is so that the start offset passed 116 * to ocfs2_find_next_bit_set() is one greater than the previously 117 * found bit. 118 */ 119 for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++) 120 { 121 /* 122 * i is the offset in this hunk, nr + i is the total bit 123 * offset. 124 */ 125 b = calc_code_bit(nr + i, &p); 126 127 /* 128 * Data bits in the resultant code are checked by 129 * parity bits that are part of the bit number 130 * representation. Huh? 131 * 132 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code"> 133 * In other words, the parity bit at position 2^k 134 * checks bits in positions having bit k set in 135 * their binary representation. Conversely, for 136 * instance, bit 13, i.e. 1101(2), is checked by 137 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1. 138 * </wikipedia> 139 * 140 * Note that 'k' is the _code_ bit number. 'b' in 141 * our loop. 142 */ 143 parity ^= b; 144 } 145 146 /* While the data buffer was treated as little endian, the 147 * return value is in host endian. */ 148 return parity; 149 } 150 151 u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize) 152 { 153 return ocfs2_hamming_encode(0, data, blocksize * 8, 0); 154 } 155 156 /* 157 * Like ocfs2_hamming_encode(), this can handle hunks. nr is the bit 158 * offset of the current hunk. If bit to be fixed is not part of the 159 * current hunk, this does nothing. 160 * 161 * If you only have one hunk, use ocfs2_hamming_fix_block(). 162 */ 163 void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr, 164 unsigned int fix) 165 { 166 unsigned int i, b; 167 168 BUG_ON(!d); 169 170 /* 171 * If the bit to fix has an hweight of 1, it's a parity bit. One 172 * busted parity bit is its own error. Nothing to do here. 173 */ 174 if (hweight32(fix) == 1) 175 return; 176 177 /* 178 * nr + d is the bit right past the data hunk we're looking at. 179 * If fix after that, nothing to do 180 */ 181 if (fix >= calc_code_bit(nr + d, NULL)) 182 return; 183 184 /* 185 * nr is the offset in the data hunk we're starting at. Let's 186 * start b at the offset in the code buffer. See hamming_encode() 187 * for a more detailed description of 'b'. 188 */ 189 b = calc_code_bit(nr, NULL); 190 /* If the fix is before this hunk, nothing to do */ 191 if (fix < b) 192 return; 193 194 for (i = 0; i < d; i++, b++) 195 { 196 /* Skip past parity bits */ 197 while (hweight32(b) == 1) 198 b++; 199 200 /* 201 * i is the offset in this data hunk. 202 * nr + i is the offset in the total data buffer. 203 * b is the offset in the total code buffer. 204 * 205 * Thus, when b == fix, bit i in the current hunk needs 206 * fixing. 207 */ 208 if (b == fix) 209 { 210 if (ocfs2_test_bit(i, data)) 211 ocfs2_clear_bit(i, data); 212 else 213 ocfs2_set_bit(i, data); 214 break; 215 } 216 } 217 } 218 219 void ocfs2_hamming_fix_block(void *data, unsigned int blocksize, 220 unsigned int fix) 221 { 222 ocfs2_hamming_fix(data, blocksize * 8, 0, fix); 223 } 224 225 /* 226 * This function generates check information for a block. 227 * data is the block to be checked. bc is a pointer to the 228 * ocfs2_block_check structure describing the crc32 and the ecc. 229 * 230 * bc should be a pointer inside data, as the function will 231 * take care of zeroing it before calculating the check information. If 232 * bc does not point inside data, the caller must make sure any inline 233 * ocfs2_block_check structures are zeroed. 234 * 235 * The data buffer must be in on-disk endian (little endian for ocfs2). 236 * bc will be filled with little-endian values and will be ready to go to 237 * disk. 238 */ 239 void ocfs2_block_check_compute(void *data, size_t blocksize, 240 struct ocfs2_block_check *bc) 241 { 242 u32 crc; 243 u32 ecc; 244 245 memset(bc, 0, sizeof(struct ocfs2_block_check)); 246 247 crc = crc32_le(~0, data, blocksize); 248 ecc = ocfs2_hamming_encode_block(data, blocksize); 249 250 /* 251 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no 252 * larger than 16 bits. 253 */ 254 BUG_ON(ecc > USHORT_MAX); 255 256 bc->bc_crc32e = cpu_to_le32(crc); 257 bc->bc_ecc = cpu_to_le16((u16)ecc); 258 } 259 260 /* 261 * This function validates existing check information. Like _compute, 262 * the function will take care of zeroing bc before calculating check codes. 263 * If bc is not a pointer inside data, the caller must have zeroed any 264 * inline ocfs2_block_check structures. 265 * 266 * Again, the data passed in should be the on-disk endian. 267 */ 268 int ocfs2_block_check_validate(void *data, size_t blocksize, 269 struct ocfs2_block_check *bc) 270 { 271 int rc = 0; 272 struct ocfs2_block_check check; 273 u32 crc, ecc; 274 275 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e); 276 check.bc_ecc = le16_to_cpu(bc->bc_ecc); 277 278 memset(bc, 0, sizeof(struct ocfs2_block_check)); 279 280 /* Fast path - if the crc32 validates, we're good to go */ 281 crc = crc32_le(~0, data, blocksize); 282 if (crc == check.bc_crc32e) 283 goto out; 284 285 mlog(ML_ERROR, 286 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n", 287 (unsigned int)check.bc_crc32e, (unsigned int)crc); 288 289 /* Ok, try ECC fixups */ 290 ecc = ocfs2_hamming_encode_block(data, blocksize); 291 ocfs2_hamming_fix_block(data, blocksize, ecc ^ check.bc_ecc); 292 293 /* And check the crc32 again */ 294 crc = crc32_le(~0, data, blocksize); 295 if (crc == check.bc_crc32e) 296 goto out; 297 298 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n", 299 (unsigned int)check.bc_crc32e, (unsigned int)crc); 300 301 rc = -EIO; 302 303 out: 304 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e); 305 bc->bc_ecc = cpu_to_le16(check.bc_ecc); 306 307 return rc; 308 } 309 310 /* 311 * This function generates check information for a list of buffer_heads. 312 * bhs is the blocks to be checked. bc is a pointer to the 313 * ocfs2_block_check structure describing the crc32 and the ecc. 314 * 315 * bc should be a pointer inside data, as the function will 316 * take care of zeroing it before calculating the check information. If 317 * bc does not point inside data, the caller must make sure any inline 318 * ocfs2_block_check structures are zeroed. 319 * 320 * The data buffer must be in on-disk endian (little endian for ocfs2). 321 * bc will be filled with little-endian values and will be ready to go to 322 * disk. 323 */ 324 void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr, 325 struct ocfs2_block_check *bc) 326 { 327 int i; 328 u32 crc, ecc; 329 330 BUG_ON(nr < 0); 331 332 if (!nr) 333 return; 334 335 memset(bc, 0, sizeof(struct ocfs2_block_check)); 336 337 for (i = 0, crc = ~0, ecc = 0; i < nr; i++) { 338 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); 339 /* 340 * The number of bits in a buffer is obviously b_size*8. 341 * The offset of this buffer is b_size*i, so the bit offset 342 * of this buffer is b_size*8*i. 343 */ 344 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data, 345 bhs[i]->b_size * 8, 346 bhs[i]->b_size * 8 * i); 347 } 348 349 /* 350 * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no 351 * larger than 16 bits. 352 */ 353 BUG_ON(ecc > USHORT_MAX); 354 355 bc->bc_crc32e = cpu_to_le32(crc); 356 bc->bc_ecc = cpu_to_le16((u16)ecc); 357 } 358 359 /* 360 * This function validates existing check information on a list of 361 * buffer_heads. Like _compute_bhs, the function will take care of 362 * zeroing bc before calculating check codes. If bc is not a pointer 363 * inside data, the caller must have zeroed any inline 364 * ocfs2_block_check structures. 365 * 366 * Again, the data passed in should be the on-disk endian. 367 */ 368 int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr, 369 struct ocfs2_block_check *bc) 370 { 371 int i, rc = 0; 372 struct ocfs2_block_check check; 373 u32 crc, ecc, fix; 374 375 BUG_ON(nr < 0); 376 377 if (!nr) 378 return 0; 379 380 check.bc_crc32e = le32_to_cpu(bc->bc_crc32e); 381 check.bc_ecc = le16_to_cpu(bc->bc_ecc); 382 383 memset(bc, 0, sizeof(struct ocfs2_block_check)); 384 385 /* Fast path - if the crc32 validates, we're good to go */ 386 for (i = 0, crc = ~0; i < nr; i++) 387 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); 388 if (crc == check.bc_crc32e) 389 goto out; 390 391 mlog(ML_ERROR, 392 "CRC32 failed: stored: %u, computed %u. Applying ECC.\n", 393 (unsigned int)check.bc_crc32e, (unsigned int)crc); 394 395 /* Ok, try ECC fixups */ 396 for (i = 0, ecc = 0; i < nr; i++) { 397 /* 398 * The number of bits in a buffer is obviously b_size*8. 399 * The offset of this buffer is b_size*i, so the bit offset 400 * of this buffer is b_size*8*i. 401 */ 402 ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data, 403 bhs[i]->b_size * 8, 404 bhs[i]->b_size * 8 * i); 405 } 406 fix = ecc ^ check.bc_ecc; 407 for (i = 0; i < nr; i++) { 408 /* 409 * Try the fix against each buffer. It will only affect 410 * one of them. 411 */ 412 ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8, 413 bhs[i]->b_size * 8 * i, fix); 414 } 415 416 /* And check the crc32 again */ 417 for (i = 0, crc = ~0; i < nr; i++) 418 crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size); 419 if (crc == check.bc_crc32e) 420 goto out; 421 422 mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n", 423 (unsigned int)check.bc_crc32e, (unsigned int)crc); 424 425 rc = -EIO; 426 427 out: 428 bc->bc_crc32e = cpu_to_le32(check.bc_crc32e); 429 bc->bc_ecc = cpu_to_le16(check.bc_ecc); 430 431 return rc; 432 } 433 434 /* 435 * These are the main API. They check the superblock flag before 436 * calling the underlying operations. 437 * 438 * They expect the buffer(s) to be in disk format. 439 */ 440 void ocfs2_compute_meta_ecc(struct super_block *sb, void *data, 441 struct ocfs2_block_check *bc) 442 { 443 if (ocfs2_meta_ecc(OCFS2_SB(sb))) 444 ocfs2_block_check_compute(data, sb->s_blocksize, bc); 445 } 446 447 int ocfs2_validate_meta_ecc(struct super_block *sb, void *data, 448 struct ocfs2_block_check *bc) 449 { 450 int rc = 0; 451 452 if (ocfs2_meta_ecc(OCFS2_SB(sb))) 453 rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc); 454 455 return rc; 456 } 457 458 void ocfs2_compute_meta_ecc_bhs(struct super_block *sb, 459 struct buffer_head **bhs, int nr, 460 struct ocfs2_block_check *bc) 461 { 462 if (ocfs2_meta_ecc(OCFS2_SB(sb))) 463 ocfs2_block_check_compute_bhs(bhs, nr, bc); 464 } 465 466 int ocfs2_validate_meta_ecc_bhs(struct super_block *sb, 467 struct buffer_head **bhs, int nr, 468 struct ocfs2_block_check *bc) 469 { 470 int rc = 0; 471 472 if (ocfs2_meta_ecc(OCFS2_SB(sb))) 473 rc = ocfs2_block_check_validate_bhs(bhs, nr, bc); 474 475 return rc; 476 } 477 478