linux/fs/ocfs2/blockcheck.c
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   1// SPDX-License-Identifier: GPL-2.0-only
   2/* -*- mode: c; c-basic-offset: 8; -*-
   3 * vim: noexpandtab sw=8 ts=8 sts=0:
   4 *
   5 * blockcheck.c
   6 *
   7 * Checksum and ECC codes for the OCFS2 userspace library.
   8 *
   9 * Copyright (C) 2006, 2008 Oracle.  All rights reserved.
  10 */
  11
  12#include <linux/kernel.h>
  13#include <linux/types.h>
  14#include <linux/crc32.h>
  15#include <linux/buffer_head.h>
  16#include <linux/bitops.h>
  17#include <linux/debugfs.h>
  18#include <linux/module.h>
  19#include <linux/fs.h>
  20#include <asm/byteorder.h>
  21
  22#include <cluster/masklog.h>
  23
  24#include "ocfs2.h"
  25
  26#include "blockcheck.h"
  27
  28
  29/*
  30 * We use the following conventions:
  31 *
  32 * d = # data bits
  33 * p = # parity bits
  34 * c = # total code bits (d + p)
  35 */
  36
  37
  38/*
  39 * Calculate the bit offset in the hamming code buffer based on the bit's
  40 * offset in the data buffer.  Since the hamming code reserves all
  41 * power-of-two bits for parity, the data bit number and the code bit
  42 * number are offset by all the parity bits beforehand.
  43 *
  44 * Recall that bit numbers in hamming code are 1-based.  This function
  45 * takes the 0-based data bit from the caller.
  46 *
  47 * An example.  Take bit 1 of the data buffer.  1 is a power of two (2^0),
  48 * so it's a parity bit.  2 is a power of two (2^1), so it's a parity bit.
  49 * 3 is not a power of two.  So bit 1 of the data buffer ends up as bit 3
  50 * in the code buffer.
  51 *
  52 * The caller can pass in *p if it wants to keep track of the most recent
  53 * number of parity bits added.  This allows the function to start the
  54 * calculation at the last place.
  55 */
  56static unsigned int calc_code_bit(unsigned int i, unsigned int *p_cache)
  57{
  58        unsigned int b, p = 0;
  59
  60        /*
  61         * Data bits are 0-based, but we're talking code bits, which
  62         * are 1-based.
  63         */
  64        b = i + 1;
  65
  66        /* Use the cache if it is there */
  67        if (p_cache)
  68                p = *p_cache;
  69        b += p;
  70
  71        /*
  72         * For every power of two below our bit number, bump our bit.
  73         *
  74         * We compare with (b + 1) because we have to compare with what b
  75         * would be _if_ it were bumped up by the parity bit.  Capice?
  76         *
  77         * p is set above.
  78         */
  79        for (; (1 << p) < (b + 1); p++)
  80                b++;
  81
  82        if (p_cache)
  83                *p_cache = p;
  84
  85        return b;
  86}
  87
  88/*
  89 * This is the low level encoder function.  It can be called across
  90 * multiple hunks just like the crc32 code.  'd' is the number of bits
  91 * _in_this_hunk_.  nr is the bit offset of this hunk.  So, if you had
  92 * two 512B buffers, you would do it like so:
  93 *
  94 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
  95 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
  96 *
  97 * If you just have one buffer, use ocfs2_hamming_encode_block().
  98 */
  99u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
 100{
 101        unsigned int i, b, p = 0;
 102
 103        BUG_ON(!d);
 104
 105        /*
 106         * b is the hamming code bit number.  Hamming code specifies a
 107         * 1-based array, but C uses 0-based.  So 'i' is for C, and 'b' is
 108         * for the algorithm.
 109         *
 110         * The i++ in the for loop is so that the start offset passed
 111         * to ocfs2_find_next_bit_set() is one greater than the previously
 112         * found bit.
 113         */
 114        for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
 115        {
 116                /*
 117                 * i is the offset in this hunk, nr + i is the total bit
 118                 * offset.
 119                 */
 120                b = calc_code_bit(nr + i, &p);
 121
 122                /*
 123                 * Data bits in the resultant code are checked by
 124                 * parity bits that are part of the bit number
 125                 * representation.  Huh?
 126                 *
 127                 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
 128                 * In other words, the parity bit at position 2^k
 129                 * checks bits in positions having bit k set in
 130                 * their binary representation.  Conversely, for
 131                 * instance, bit 13, i.e. 1101(2), is checked by
 132                 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
 133                 * </wikipedia>
 134                 *
 135                 * Note that 'k' is the _code_ bit number.  'b' in
 136                 * our loop.
 137                 */
 138                parity ^= b;
 139        }
 140
 141        /* While the data buffer was treated as little endian, the
 142         * return value is in host endian. */
 143        return parity;
 144}
 145
 146u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
 147{
 148        return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
 149}
 150
 151/*
 152 * Like ocfs2_hamming_encode(), this can handle hunks.  nr is the bit
 153 * offset of the current hunk.  If bit to be fixed is not part of the
 154 * current hunk, this does nothing.
 155 *
 156 * If you only have one hunk, use ocfs2_hamming_fix_block().
 157 */
 158void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
 159                       unsigned int fix)
 160{
 161        unsigned int i, b;
 162
 163        BUG_ON(!d);
 164
 165        /*
 166         * If the bit to fix has an hweight of 1, it's a parity bit.  One
 167         * busted parity bit is its own error.  Nothing to do here.
 168         */
 169        if (hweight32(fix) == 1)
 170                return;
 171
 172        /*
 173         * nr + d is the bit right past the data hunk we're looking at.
 174         * If fix after that, nothing to do
 175         */
 176        if (fix >= calc_code_bit(nr + d, NULL))
 177                return;
 178
 179        /*
 180         * nr is the offset in the data hunk we're starting at.  Let's
 181         * start b at the offset in the code buffer.  See hamming_encode()
 182         * for a more detailed description of 'b'.
 183         */
 184        b = calc_code_bit(nr, NULL);
 185        /* If the fix is before this hunk, nothing to do */
 186        if (fix < b)
 187                return;
 188
 189        for (i = 0; i < d; i++, b++)
 190        {
 191                /* Skip past parity bits */
 192                while (hweight32(b) == 1)
 193                        b++;
 194
 195                /*
 196                 * i is the offset in this data hunk.
 197                 * nr + i is the offset in the total data buffer.
 198                 * b is the offset in the total code buffer.
 199                 *
 200                 * Thus, when b == fix, bit i in the current hunk needs
 201                 * fixing.
 202                 */
 203                if (b == fix)
 204                {
 205                        if (ocfs2_test_bit(i, data))
 206                                ocfs2_clear_bit(i, data);
 207                        else
 208                                ocfs2_set_bit(i, data);
 209                        break;
 210                }
 211        }
 212}
 213
 214void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
 215                             unsigned int fix)
 216{
 217        ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
 218}
 219
 220
 221/*
 222 * Debugfs handling.
 223 */
 224
 225#ifdef CONFIG_DEBUG_FS
 226
 227static int blockcheck_u64_get(void *data, u64 *val)
 228{
 229        *val = *(u64 *)data;
 230        return 0;
 231}
 232DEFINE_SIMPLE_ATTRIBUTE(blockcheck_fops, blockcheck_u64_get, NULL, "%llu\n");
 233
 234static void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
 235{
 236        if (stats) {
 237                debugfs_remove_recursive(stats->b_debug_dir);
 238                stats->b_debug_dir = NULL;
 239        }
 240}
 241
 242static void ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
 243                                           struct dentry *parent)
 244{
 245        struct dentry *dir;
 246
 247        dir = debugfs_create_dir("blockcheck", parent);
 248        stats->b_debug_dir = dir;
 249
 250        debugfs_create_file("blocks_checked", S_IFREG | S_IRUSR, dir,
 251                            &stats->b_check_count, &blockcheck_fops);
 252
 253        debugfs_create_file("checksums_failed", S_IFREG | S_IRUSR, dir,
 254                            &stats->b_failure_count, &blockcheck_fops);
 255
 256        debugfs_create_file("ecc_recoveries", S_IFREG | S_IRUSR, dir,
 257                            &stats->b_recover_count, &blockcheck_fops);
 258
 259}
 260#else
 261static inline void ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
 262                                                  struct dentry *parent)
 263{
 264}
 265
 266static inline void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
 267{
 268}
 269#endif  /* CONFIG_DEBUG_FS */
 270
 271/* Always-called wrappers for starting and stopping the debugfs files */
 272void ocfs2_blockcheck_stats_debugfs_install(struct ocfs2_blockcheck_stats *stats,
 273                                            struct dentry *parent)
 274{
 275        ocfs2_blockcheck_debug_install(stats, parent);
 276}
 277
 278void ocfs2_blockcheck_stats_debugfs_remove(struct ocfs2_blockcheck_stats *stats)
 279{
 280        ocfs2_blockcheck_debug_remove(stats);
 281}
 282
 283static void ocfs2_blockcheck_inc_check(struct ocfs2_blockcheck_stats *stats)
 284{
 285        u64 new_count;
 286
 287        if (!stats)
 288                return;
 289
 290        spin_lock(&stats->b_lock);
 291        stats->b_check_count++;
 292        new_count = stats->b_check_count;
 293        spin_unlock(&stats->b_lock);
 294
 295        if (!new_count)
 296                mlog(ML_NOTICE, "Block check count has wrapped\n");
 297}
 298
 299static void ocfs2_blockcheck_inc_failure(struct ocfs2_blockcheck_stats *stats)
 300{
 301        u64 new_count;
 302
 303        if (!stats)
 304                return;
 305
 306        spin_lock(&stats->b_lock);
 307        stats->b_failure_count++;
 308        new_count = stats->b_failure_count;
 309        spin_unlock(&stats->b_lock);
 310
 311        if (!new_count)
 312                mlog(ML_NOTICE, "Checksum failure count has wrapped\n");
 313}
 314
 315static void ocfs2_blockcheck_inc_recover(struct ocfs2_blockcheck_stats *stats)
 316{
 317        u64 new_count;
 318
 319        if (!stats)
 320                return;
 321
 322        spin_lock(&stats->b_lock);
 323        stats->b_recover_count++;
 324        new_count = stats->b_recover_count;
 325        spin_unlock(&stats->b_lock);
 326
 327        if (!new_count)
 328                mlog(ML_NOTICE, "ECC recovery count has wrapped\n");
 329}
 330
 331
 332
 333/*
 334 * These are the low-level APIs for using the ocfs2_block_check structure.
 335 */
 336
 337/*
 338 * This function generates check information for a block.
 339 * data is the block to be checked.  bc is a pointer to the
 340 * ocfs2_block_check structure describing the crc32 and the ecc.
 341 *
 342 * bc should be a pointer inside data, as the function will
 343 * take care of zeroing it before calculating the check information.  If
 344 * bc does not point inside data, the caller must make sure any inline
 345 * ocfs2_block_check structures are zeroed.
 346 *
 347 * The data buffer must be in on-disk endian (little endian for ocfs2).
 348 * bc will be filled with little-endian values and will be ready to go to
 349 * disk.
 350 */
 351void ocfs2_block_check_compute(void *data, size_t blocksize,
 352                               struct ocfs2_block_check *bc)
 353{
 354        u32 crc;
 355        u32 ecc;
 356
 357        memset(bc, 0, sizeof(struct ocfs2_block_check));
 358
 359        crc = crc32_le(~0, data, blocksize);
 360        ecc = ocfs2_hamming_encode_block(data, blocksize);
 361
 362        /*
 363         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
 364         * larger than 16 bits.
 365         */
 366        BUG_ON(ecc > USHRT_MAX);
 367
 368        bc->bc_crc32e = cpu_to_le32(crc);
 369        bc->bc_ecc = cpu_to_le16((u16)ecc);
 370}
 371
 372/*
 373 * This function validates existing check information.  Like _compute,
 374 * the function will take care of zeroing bc before calculating check codes.
 375 * If bc is not a pointer inside data, the caller must have zeroed any
 376 * inline ocfs2_block_check structures.
 377 *
 378 * Again, the data passed in should be the on-disk endian.
 379 */
 380int ocfs2_block_check_validate(void *data, size_t blocksize,
 381                               struct ocfs2_block_check *bc,
 382                               struct ocfs2_blockcheck_stats *stats)
 383{
 384        int rc = 0;
 385        u32 bc_crc32e;
 386        u16 bc_ecc;
 387        u32 crc, ecc;
 388
 389        ocfs2_blockcheck_inc_check(stats);
 390
 391        bc_crc32e = le32_to_cpu(bc->bc_crc32e);
 392        bc_ecc = le16_to_cpu(bc->bc_ecc);
 393
 394        memset(bc, 0, sizeof(struct ocfs2_block_check));
 395
 396        /* Fast path - if the crc32 validates, we're good to go */
 397        crc = crc32_le(~0, data, blocksize);
 398        if (crc == bc_crc32e)
 399                goto out;
 400
 401        ocfs2_blockcheck_inc_failure(stats);
 402        mlog(ML_ERROR,
 403             "CRC32 failed: stored: 0x%x, computed 0x%x. Applying ECC.\n",
 404             (unsigned int)bc_crc32e, (unsigned int)crc);
 405
 406        /* Ok, try ECC fixups */
 407        ecc = ocfs2_hamming_encode_block(data, blocksize);
 408        ocfs2_hamming_fix_block(data, blocksize, ecc ^ bc_ecc);
 409
 410        /* And check the crc32 again */
 411        crc = crc32_le(~0, data, blocksize);
 412        if (crc == bc_crc32e) {
 413                ocfs2_blockcheck_inc_recover(stats);
 414                goto out;
 415        }
 416
 417        mlog(ML_ERROR, "Fixed CRC32 failed: stored: 0x%x, computed 0x%x\n",
 418             (unsigned int)bc_crc32e, (unsigned int)crc);
 419
 420        rc = -EIO;
 421
 422out:
 423        bc->bc_crc32e = cpu_to_le32(bc_crc32e);
 424        bc->bc_ecc = cpu_to_le16(bc_ecc);
 425
 426        return rc;
 427}
 428
 429/*
 430 * This function generates check information for a list of buffer_heads.
 431 * bhs is the blocks to be checked.  bc is a pointer to the
 432 * ocfs2_block_check structure describing the crc32 and the ecc.
 433 *
 434 * bc should be a pointer inside data, as the function will
 435 * take care of zeroing it before calculating the check information.  If
 436 * bc does not point inside data, the caller must make sure any inline
 437 * ocfs2_block_check structures are zeroed.
 438 *
 439 * The data buffer must be in on-disk endian (little endian for ocfs2).
 440 * bc will be filled with little-endian values and will be ready to go to
 441 * disk.
 442 */
 443void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
 444                                   struct ocfs2_block_check *bc)
 445{
 446        int i;
 447        u32 crc, ecc;
 448
 449        BUG_ON(nr < 0);
 450
 451        if (!nr)
 452                return;
 453
 454        memset(bc, 0, sizeof(struct ocfs2_block_check));
 455
 456        for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
 457                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 458                /*
 459                 * The number of bits in a buffer is obviously b_size*8.
 460                 * The offset of this buffer is b_size*i, so the bit offset
 461                 * of this buffer is b_size*8*i.
 462                 */
 463                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
 464                                                bhs[i]->b_size * 8,
 465                                                bhs[i]->b_size * 8 * i);
 466        }
 467
 468        /*
 469         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
 470         * larger than 16 bits.
 471         */
 472        BUG_ON(ecc > USHRT_MAX);
 473
 474        bc->bc_crc32e = cpu_to_le32(crc);
 475        bc->bc_ecc = cpu_to_le16((u16)ecc);
 476}
 477
 478/*
 479 * This function validates existing check information on a list of
 480 * buffer_heads.  Like _compute_bhs, the function will take care of
 481 * zeroing bc before calculating check codes.  If bc is not a pointer
 482 * inside data, the caller must have zeroed any inline
 483 * ocfs2_block_check structures.
 484 *
 485 * Again, the data passed in should be the on-disk endian.
 486 */
 487int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
 488                                   struct ocfs2_block_check *bc,
 489                                   struct ocfs2_blockcheck_stats *stats)
 490{
 491        int i, rc = 0;
 492        u32 bc_crc32e;
 493        u16 bc_ecc;
 494        u32 crc, ecc, fix;
 495
 496        BUG_ON(nr < 0);
 497
 498        if (!nr)
 499                return 0;
 500
 501        ocfs2_blockcheck_inc_check(stats);
 502
 503        bc_crc32e = le32_to_cpu(bc->bc_crc32e);
 504        bc_ecc = le16_to_cpu(bc->bc_ecc);
 505
 506        memset(bc, 0, sizeof(struct ocfs2_block_check));
 507
 508        /* Fast path - if the crc32 validates, we're good to go */
 509        for (i = 0, crc = ~0; i < nr; i++)
 510                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 511        if (crc == bc_crc32e)
 512                goto out;
 513
 514        ocfs2_blockcheck_inc_failure(stats);
 515        mlog(ML_ERROR,
 516             "CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
 517             (unsigned int)bc_crc32e, (unsigned int)crc);
 518
 519        /* Ok, try ECC fixups */
 520        for (i = 0, ecc = 0; i < nr; i++) {
 521                /*
 522                 * The number of bits in a buffer is obviously b_size*8.
 523                 * The offset of this buffer is b_size*i, so the bit offset
 524                 * of this buffer is b_size*8*i.
 525                 */
 526                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
 527                                                bhs[i]->b_size * 8,
 528                                                bhs[i]->b_size * 8 * i);
 529        }
 530        fix = ecc ^ bc_ecc;
 531        for (i = 0; i < nr; i++) {
 532                /*
 533                 * Try the fix against each buffer.  It will only affect
 534                 * one of them.
 535                 */
 536                ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
 537                                  bhs[i]->b_size * 8 * i, fix);
 538        }
 539
 540        /* And check the crc32 again */
 541        for (i = 0, crc = ~0; i < nr; i++)
 542                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 543        if (crc == bc_crc32e) {
 544                ocfs2_blockcheck_inc_recover(stats);
 545                goto out;
 546        }
 547
 548        mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
 549             (unsigned int)bc_crc32e, (unsigned int)crc);
 550
 551        rc = -EIO;
 552
 553out:
 554        bc->bc_crc32e = cpu_to_le32(bc_crc32e);
 555        bc->bc_ecc = cpu_to_le16(bc_ecc);
 556
 557        return rc;
 558}
 559
 560/*
 561 * These are the main API.  They check the superblock flag before
 562 * calling the underlying operations.
 563 *
 564 * They expect the buffer(s) to be in disk format.
 565 */
 566void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
 567                            struct ocfs2_block_check *bc)
 568{
 569        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
 570                ocfs2_block_check_compute(data, sb->s_blocksize, bc);
 571}
 572
 573int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
 574                            struct ocfs2_block_check *bc)
 575{
 576        int rc = 0;
 577        struct ocfs2_super *osb = OCFS2_SB(sb);
 578
 579        if (ocfs2_meta_ecc(osb))
 580                rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc,
 581                                                &osb->osb_ecc_stats);
 582
 583        return rc;
 584}
 585
 586void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
 587                                struct buffer_head **bhs, int nr,
 588                                struct ocfs2_block_check *bc)
 589{
 590        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
 591                ocfs2_block_check_compute_bhs(bhs, nr, bc);
 592}
 593
 594int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
 595                                struct buffer_head **bhs, int nr,
 596                                struct ocfs2_block_check *bc)
 597{
 598        int rc = 0;
 599        struct ocfs2_super *osb = OCFS2_SB(sb);
 600
 601        if (ocfs2_meta_ecc(osb))
 602                rc = ocfs2_block_check_validate_bhs(bhs, nr, bc,
 603                                                    &osb->osb_ecc_stats);
 604
 605        return rc;
 606}
 607
 608