linux/fs/ocfs2/blockcheck.c
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   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 <linux/debugfs.h>
  26#include <linux/module.h>
  27#include <linux/fs.h>
  28#include <asm/byteorder.h>
  29
  30#include <cluster/masklog.h>
  31
  32#include "ocfs2.h"
  33
  34#include "blockcheck.h"
  35
  36
  37/*
  38 * We use the following conventions:
  39 *
  40 * d = # data bits
  41 * p = # parity bits
  42 * c = # total code bits (d + p)
  43 */
  44
  45
  46/*
  47 * Calculate the bit offset in the hamming code buffer based on the bit's
  48 * offset in the data buffer.  Since the hamming code reserves all
  49 * power-of-two bits for parity, the data bit number and the code bit
  50 * number are offset by all the parity bits beforehand.
  51 *
  52 * Recall that bit numbers in hamming code are 1-based.  This function
  53 * takes the 0-based data bit from the caller.
  54 *
  55 * An example.  Take bit 1 of the data buffer.  1 is a power of two (2^0),
  56 * so it's a parity bit.  2 is a power of two (2^1), so it's a parity bit.
  57 * 3 is not a power of two.  So bit 1 of the data buffer ends up as bit 3
  58 * in the code buffer.
  59 *
  60 * The caller can pass in *p if it wants to keep track of the most recent
  61 * number of parity bits added.  This allows the function to start the
  62 * calculation at the last place.
  63 */
  64static unsigned int calc_code_bit(unsigned int i, unsigned int *p_cache)
  65{
  66        unsigned int b, p = 0;
  67
  68        /*
  69         * Data bits are 0-based, but we're talking code bits, which
  70         * are 1-based.
  71         */
  72        b = i + 1;
  73
  74        /* Use the cache if it is there */
  75        if (p_cache)
  76                p = *p_cache;
  77        b += p;
  78
  79        /*
  80         * For every power of two below our bit number, bump our bit.
  81         *
  82         * We compare with (b + 1) because we have to compare with what b
  83         * would be _if_ it were bumped up by the parity bit.  Capice?
  84         *
  85         * p is set above.
  86         */
  87        for (; (1 << p) < (b + 1); p++)
  88                b++;
  89
  90        if (p_cache)
  91                *p_cache = p;
  92
  93        return b;
  94}
  95
  96/*
  97 * This is the low level encoder function.  It can be called across
  98 * multiple hunks just like the crc32 code.  'd' is the number of bits
  99 * _in_this_hunk_.  nr is the bit offset of this hunk.  So, if you had
 100 * two 512B buffers, you would do it like so:
 101 *
 102 * parity = ocfs2_hamming_encode(0, buf1, 512 * 8, 0);
 103 * parity = ocfs2_hamming_encode(parity, buf2, 512 * 8, 512 * 8);
 104 *
 105 * If you just have one buffer, use ocfs2_hamming_encode_block().
 106 */
 107u32 ocfs2_hamming_encode(u32 parity, void *data, unsigned int d, unsigned int nr)
 108{
 109        unsigned int i, b, p = 0;
 110
 111        BUG_ON(!d);
 112
 113        /*
 114         * b is the hamming code bit number.  Hamming code specifies a
 115         * 1-based array, but C uses 0-based.  So 'i' is for C, and 'b' is
 116         * for the algorithm.
 117         *
 118         * The i++ in the for loop is so that the start offset passed
 119         * to ocfs2_find_next_bit_set() is one greater than the previously
 120         * found bit.
 121         */
 122        for (i = 0; (i = ocfs2_find_next_bit(data, d, i)) < d; i++)
 123        {
 124                /*
 125                 * i is the offset in this hunk, nr + i is the total bit
 126                 * offset.
 127                 */
 128                b = calc_code_bit(nr + i, &p);
 129
 130                /*
 131                 * Data bits in the resultant code are checked by
 132                 * parity bits that are part of the bit number
 133                 * representation.  Huh?
 134                 *
 135                 * <wikipedia href="http://en.wikipedia.org/wiki/Hamming_code">
 136                 * In other words, the parity bit at position 2^k
 137                 * checks bits in positions having bit k set in
 138                 * their binary representation.  Conversely, for
 139                 * instance, bit 13, i.e. 1101(2), is checked by
 140                 * bits 1000(2) = 8, 0100(2)=4 and 0001(2) = 1.
 141                 * </wikipedia>
 142                 *
 143                 * Note that 'k' is the _code_ bit number.  'b' in
 144                 * our loop.
 145                 */
 146                parity ^= b;
 147        }
 148
 149        /* While the data buffer was treated as little endian, the
 150         * return value is in host endian. */
 151        return parity;
 152}
 153
 154u32 ocfs2_hamming_encode_block(void *data, unsigned int blocksize)
 155{
 156        return ocfs2_hamming_encode(0, data, blocksize * 8, 0);
 157}
 158
 159/*
 160 * Like ocfs2_hamming_encode(), this can handle hunks.  nr is the bit
 161 * offset of the current hunk.  If bit to be fixed is not part of the
 162 * current hunk, this does nothing.
 163 *
 164 * If you only have one hunk, use ocfs2_hamming_fix_block().
 165 */
 166void ocfs2_hamming_fix(void *data, unsigned int d, unsigned int nr,
 167                       unsigned int fix)
 168{
 169        unsigned int i, b;
 170
 171        BUG_ON(!d);
 172
 173        /*
 174         * If the bit to fix has an hweight of 1, it's a parity bit.  One
 175         * busted parity bit is its own error.  Nothing to do here.
 176         */
 177        if (hweight32(fix) == 1)
 178                return;
 179
 180        /*
 181         * nr + d is the bit right past the data hunk we're looking at.
 182         * If fix after that, nothing to do
 183         */
 184        if (fix >= calc_code_bit(nr + d, NULL))
 185                return;
 186
 187        /*
 188         * nr is the offset in the data hunk we're starting at.  Let's
 189         * start b at the offset in the code buffer.  See hamming_encode()
 190         * for a more detailed description of 'b'.
 191         */
 192        b = calc_code_bit(nr, NULL);
 193        /* If the fix is before this hunk, nothing to do */
 194        if (fix < b)
 195                return;
 196
 197        for (i = 0; i < d; i++, b++)
 198        {
 199                /* Skip past parity bits */
 200                while (hweight32(b) == 1)
 201                        b++;
 202
 203                /*
 204                 * i is the offset in this data hunk.
 205                 * nr + i is the offset in the total data buffer.
 206                 * b is the offset in the total code buffer.
 207                 *
 208                 * Thus, when b == fix, bit i in the current hunk needs
 209                 * fixing.
 210                 */
 211                if (b == fix)
 212                {
 213                        if (ocfs2_test_bit(i, data))
 214                                ocfs2_clear_bit(i, data);
 215                        else
 216                                ocfs2_set_bit(i, data);
 217                        break;
 218                }
 219        }
 220}
 221
 222void ocfs2_hamming_fix_block(void *data, unsigned int blocksize,
 223                             unsigned int fix)
 224{
 225        ocfs2_hamming_fix(data, blocksize * 8, 0, fix);
 226}
 227
 228
 229/*
 230 * Debugfs handling.
 231 */
 232
 233#ifdef CONFIG_DEBUG_FS
 234
 235static int blockcheck_u64_get(void *data, u64 *val)
 236{
 237        *val = *(u64 *)data;
 238        return 0;
 239}
 240DEFINE_SIMPLE_ATTRIBUTE(blockcheck_fops, blockcheck_u64_get, NULL, "%llu\n");
 241
 242static struct dentry *blockcheck_debugfs_create(const char *name,
 243                                                struct dentry *parent,
 244                                                u64 *value)
 245{
 246        return debugfs_create_file(name, S_IFREG | S_IRUSR, parent, value,
 247                                   &blockcheck_fops);
 248}
 249
 250static void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
 251{
 252        if (stats) {
 253                debugfs_remove(stats->b_debug_check);
 254                stats->b_debug_check = NULL;
 255                debugfs_remove(stats->b_debug_failure);
 256                stats->b_debug_failure = NULL;
 257                debugfs_remove(stats->b_debug_recover);
 258                stats->b_debug_recover = NULL;
 259                debugfs_remove(stats->b_debug_dir);
 260                stats->b_debug_dir = NULL;
 261        }
 262}
 263
 264static int ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
 265                                          struct dentry *parent)
 266{
 267        int rc = -EINVAL;
 268
 269        if (!stats)
 270                goto out;
 271
 272        stats->b_debug_dir = debugfs_create_dir("blockcheck", parent);
 273        if (!stats->b_debug_dir)
 274                goto out;
 275
 276        stats->b_debug_check =
 277                blockcheck_debugfs_create("blocks_checked",
 278                                          stats->b_debug_dir,
 279                                          &stats->b_check_count);
 280
 281        stats->b_debug_failure =
 282                blockcheck_debugfs_create("checksums_failed",
 283                                          stats->b_debug_dir,
 284                                          &stats->b_failure_count);
 285
 286        stats->b_debug_recover =
 287                blockcheck_debugfs_create("ecc_recoveries",
 288                                          stats->b_debug_dir,
 289                                          &stats->b_recover_count);
 290        if (stats->b_debug_check && stats->b_debug_failure &&
 291            stats->b_debug_recover)
 292                rc = 0;
 293
 294out:
 295        if (rc)
 296                ocfs2_blockcheck_debug_remove(stats);
 297        return rc;
 298}
 299#else
 300static inline int ocfs2_blockcheck_debug_install(struct ocfs2_blockcheck_stats *stats,
 301                                                 struct dentry *parent)
 302{
 303        return 0;
 304}
 305
 306static inline void ocfs2_blockcheck_debug_remove(struct ocfs2_blockcheck_stats *stats)
 307{
 308}
 309#endif  /* CONFIG_DEBUG_FS */
 310
 311/* Always-called wrappers for starting and stopping the debugfs files */
 312int ocfs2_blockcheck_stats_debugfs_install(struct ocfs2_blockcheck_stats *stats,
 313                                           struct dentry *parent)
 314{
 315        return ocfs2_blockcheck_debug_install(stats, parent);
 316}
 317
 318void ocfs2_blockcheck_stats_debugfs_remove(struct ocfs2_blockcheck_stats *stats)
 319{
 320        ocfs2_blockcheck_debug_remove(stats);
 321}
 322
 323static void ocfs2_blockcheck_inc_check(struct ocfs2_blockcheck_stats *stats)
 324{
 325        u64 new_count;
 326
 327        if (!stats)
 328                return;
 329
 330        spin_lock(&stats->b_lock);
 331        stats->b_check_count++;
 332        new_count = stats->b_check_count;
 333        spin_unlock(&stats->b_lock);
 334
 335        if (!new_count)
 336                mlog(ML_NOTICE, "Block check count has wrapped\n");
 337}
 338
 339static void ocfs2_blockcheck_inc_failure(struct ocfs2_blockcheck_stats *stats)
 340{
 341        u64 new_count;
 342
 343        if (!stats)
 344                return;
 345
 346        spin_lock(&stats->b_lock);
 347        stats->b_failure_count++;
 348        new_count = stats->b_failure_count;
 349        spin_unlock(&stats->b_lock);
 350
 351        if (!new_count)
 352                mlog(ML_NOTICE, "Checksum failure count has wrapped\n");
 353}
 354
 355static void ocfs2_blockcheck_inc_recover(struct ocfs2_blockcheck_stats *stats)
 356{
 357        u64 new_count;
 358
 359        if (!stats)
 360                return;
 361
 362        spin_lock(&stats->b_lock);
 363        stats->b_recover_count++;
 364        new_count = stats->b_recover_count;
 365        spin_unlock(&stats->b_lock);
 366
 367        if (!new_count)
 368                mlog(ML_NOTICE, "ECC recovery count has wrapped\n");
 369}
 370
 371
 372
 373/*
 374 * These are the low-level APIs for using the ocfs2_block_check structure.
 375 */
 376
 377/*
 378 * This function generates check information for a block.
 379 * data is the block to be checked.  bc is a pointer to the
 380 * ocfs2_block_check structure describing the crc32 and the ecc.
 381 *
 382 * bc should be a pointer inside data, as the function will
 383 * take care of zeroing it before calculating the check information.  If
 384 * bc does not point inside data, the caller must make sure any inline
 385 * ocfs2_block_check structures are zeroed.
 386 *
 387 * The data buffer must be in on-disk endian (little endian for ocfs2).
 388 * bc will be filled with little-endian values and will be ready to go to
 389 * disk.
 390 */
 391void ocfs2_block_check_compute(void *data, size_t blocksize,
 392                               struct ocfs2_block_check *bc)
 393{
 394        u32 crc;
 395        u32 ecc;
 396
 397        memset(bc, 0, sizeof(struct ocfs2_block_check));
 398
 399        crc = crc32_le(~0, data, blocksize);
 400        ecc = ocfs2_hamming_encode_block(data, blocksize);
 401
 402        /*
 403         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
 404         * larger than 16 bits.
 405         */
 406        BUG_ON(ecc > USHRT_MAX);
 407
 408        bc->bc_crc32e = cpu_to_le32(crc);
 409        bc->bc_ecc = cpu_to_le16((u16)ecc);
 410}
 411
 412/*
 413 * This function validates existing check information.  Like _compute,
 414 * the function will take care of zeroing bc before calculating check codes.
 415 * If bc is not a pointer inside data, the caller must have zeroed any
 416 * inline ocfs2_block_check structures.
 417 *
 418 * Again, the data passed in should be the on-disk endian.
 419 */
 420int ocfs2_block_check_validate(void *data, size_t blocksize,
 421                               struct ocfs2_block_check *bc,
 422                               struct ocfs2_blockcheck_stats *stats)
 423{
 424        int rc = 0;
 425        u32 bc_crc32e;
 426        u16 bc_ecc;
 427        u32 crc, ecc;
 428
 429        ocfs2_blockcheck_inc_check(stats);
 430
 431        bc_crc32e = le32_to_cpu(bc->bc_crc32e);
 432        bc_ecc = le16_to_cpu(bc->bc_ecc);
 433
 434        memset(bc, 0, sizeof(struct ocfs2_block_check));
 435
 436        /* Fast path - if the crc32 validates, we're good to go */
 437        crc = crc32_le(~0, data, blocksize);
 438        if (crc == bc_crc32e)
 439                goto out;
 440
 441        ocfs2_blockcheck_inc_failure(stats);
 442        mlog(ML_ERROR,
 443             "CRC32 failed: stored: 0x%x, computed 0x%x. Applying ECC.\n",
 444             (unsigned int)bc_crc32e, (unsigned int)crc);
 445
 446        /* Ok, try ECC fixups */
 447        ecc = ocfs2_hamming_encode_block(data, blocksize);
 448        ocfs2_hamming_fix_block(data, blocksize, ecc ^ bc_ecc);
 449
 450        /* And check the crc32 again */
 451        crc = crc32_le(~0, data, blocksize);
 452        if (crc == bc_crc32e) {
 453                ocfs2_blockcheck_inc_recover(stats);
 454                goto out;
 455        }
 456
 457        mlog(ML_ERROR, "Fixed CRC32 failed: stored: 0x%x, computed 0x%x\n",
 458             (unsigned int)bc_crc32e, (unsigned int)crc);
 459
 460        rc = -EIO;
 461
 462out:
 463        bc->bc_crc32e = cpu_to_le32(bc_crc32e);
 464        bc->bc_ecc = cpu_to_le16(bc_ecc);
 465
 466        return rc;
 467}
 468
 469/*
 470 * This function generates check information for a list of buffer_heads.
 471 * bhs is the blocks to be checked.  bc is a pointer to the
 472 * ocfs2_block_check structure describing the crc32 and the ecc.
 473 *
 474 * bc should be a pointer inside data, as the function will
 475 * take care of zeroing it before calculating the check information.  If
 476 * bc does not point inside data, the caller must make sure any inline
 477 * ocfs2_block_check structures are zeroed.
 478 *
 479 * The data buffer must be in on-disk endian (little endian for ocfs2).
 480 * bc will be filled with little-endian values and will be ready to go to
 481 * disk.
 482 */
 483void ocfs2_block_check_compute_bhs(struct buffer_head **bhs, int nr,
 484                                   struct ocfs2_block_check *bc)
 485{
 486        int i;
 487        u32 crc, ecc;
 488
 489        BUG_ON(nr < 0);
 490
 491        if (!nr)
 492                return;
 493
 494        memset(bc, 0, sizeof(struct ocfs2_block_check));
 495
 496        for (i = 0, crc = ~0, ecc = 0; i < nr; i++) {
 497                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 498                /*
 499                 * The number of bits in a buffer is obviously b_size*8.
 500                 * The offset of this buffer is b_size*i, so the bit offset
 501                 * of this buffer is b_size*8*i.
 502                 */
 503                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
 504                                                bhs[i]->b_size * 8,
 505                                                bhs[i]->b_size * 8 * i);
 506        }
 507
 508        /*
 509         * No ecc'd ocfs2 structure is larger than 4K, so ecc will be no
 510         * larger than 16 bits.
 511         */
 512        BUG_ON(ecc > USHRT_MAX);
 513
 514        bc->bc_crc32e = cpu_to_le32(crc);
 515        bc->bc_ecc = cpu_to_le16((u16)ecc);
 516}
 517
 518/*
 519 * This function validates existing check information on a list of
 520 * buffer_heads.  Like _compute_bhs, the function will take care of
 521 * zeroing bc before calculating check codes.  If bc is not a pointer
 522 * inside data, the caller must have zeroed any inline
 523 * ocfs2_block_check structures.
 524 *
 525 * Again, the data passed in should be the on-disk endian.
 526 */
 527int ocfs2_block_check_validate_bhs(struct buffer_head **bhs, int nr,
 528                                   struct ocfs2_block_check *bc,
 529                                   struct ocfs2_blockcheck_stats *stats)
 530{
 531        int i, rc = 0;
 532        u32 bc_crc32e;
 533        u16 bc_ecc;
 534        u32 crc, ecc, fix;
 535
 536        BUG_ON(nr < 0);
 537
 538        if (!nr)
 539                return 0;
 540
 541        ocfs2_blockcheck_inc_check(stats);
 542
 543        bc_crc32e = le32_to_cpu(bc->bc_crc32e);
 544        bc_ecc = le16_to_cpu(bc->bc_ecc);
 545
 546        memset(bc, 0, sizeof(struct ocfs2_block_check));
 547
 548        /* Fast path - if the crc32 validates, we're good to go */
 549        for (i = 0, crc = ~0; i < nr; i++)
 550                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 551        if (crc == bc_crc32e)
 552                goto out;
 553
 554        ocfs2_blockcheck_inc_failure(stats);
 555        mlog(ML_ERROR,
 556             "CRC32 failed: stored: %u, computed %u.  Applying ECC.\n",
 557             (unsigned int)bc_crc32e, (unsigned int)crc);
 558
 559        /* Ok, try ECC fixups */
 560        for (i = 0, ecc = 0; i < nr; i++) {
 561                /*
 562                 * The number of bits in a buffer is obviously b_size*8.
 563                 * The offset of this buffer is b_size*i, so the bit offset
 564                 * of this buffer is b_size*8*i.
 565                 */
 566                ecc = (u16)ocfs2_hamming_encode(ecc, bhs[i]->b_data,
 567                                                bhs[i]->b_size * 8,
 568                                                bhs[i]->b_size * 8 * i);
 569        }
 570        fix = ecc ^ bc_ecc;
 571        for (i = 0; i < nr; i++) {
 572                /*
 573                 * Try the fix against each buffer.  It will only affect
 574                 * one of them.
 575                 */
 576                ocfs2_hamming_fix(bhs[i]->b_data, bhs[i]->b_size * 8,
 577                                  bhs[i]->b_size * 8 * i, fix);
 578        }
 579
 580        /* And check the crc32 again */
 581        for (i = 0, crc = ~0; i < nr; i++)
 582                crc = crc32_le(crc, bhs[i]->b_data, bhs[i]->b_size);
 583        if (crc == bc_crc32e) {
 584                ocfs2_blockcheck_inc_recover(stats);
 585                goto out;
 586        }
 587
 588        mlog(ML_ERROR, "Fixed CRC32 failed: stored: %u, computed %u\n",
 589             (unsigned int)bc_crc32e, (unsigned int)crc);
 590
 591        rc = -EIO;
 592
 593out:
 594        bc->bc_crc32e = cpu_to_le32(bc_crc32e);
 595        bc->bc_ecc = cpu_to_le16(bc_ecc);
 596
 597        return rc;
 598}
 599
 600/*
 601 * These are the main API.  They check the superblock flag before
 602 * calling the underlying operations.
 603 *
 604 * They expect the buffer(s) to be in disk format.
 605 */
 606void ocfs2_compute_meta_ecc(struct super_block *sb, void *data,
 607                            struct ocfs2_block_check *bc)
 608{
 609        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
 610                ocfs2_block_check_compute(data, sb->s_blocksize, bc);
 611}
 612
 613int ocfs2_validate_meta_ecc(struct super_block *sb, void *data,
 614                            struct ocfs2_block_check *bc)
 615{
 616        int rc = 0;
 617        struct ocfs2_super *osb = OCFS2_SB(sb);
 618
 619        if (ocfs2_meta_ecc(osb))
 620                rc = ocfs2_block_check_validate(data, sb->s_blocksize, bc,
 621                                                &osb->osb_ecc_stats);
 622
 623        return rc;
 624}
 625
 626void ocfs2_compute_meta_ecc_bhs(struct super_block *sb,
 627                                struct buffer_head **bhs, int nr,
 628                                struct ocfs2_block_check *bc)
 629{
 630        if (ocfs2_meta_ecc(OCFS2_SB(sb)))
 631                ocfs2_block_check_compute_bhs(bhs, nr, bc);
 632}
 633
 634int ocfs2_validate_meta_ecc_bhs(struct super_block *sb,
 635                                struct buffer_head **bhs, int nr,
 636                                struct ocfs2_block_check *bc)
 637{
 638        int rc = 0;
 639        struct ocfs2_super *osb = OCFS2_SB(sb);
 640
 641        if (ocfs2_meta_ecc(osb))
 642                rc = ocfs2_block_check_validate_bhs(bhs, nr, bc,
 643                                                    &osb->osb_ecc_stats);
 644
 645        return rc;
 646}
 647
 648
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