linux/fs/fat/fatent.c
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   1/*
   2 * Copyright (C) 2004, OGAWA Hirofumi
   3 * Released under GPL v2.
   4 */
   5
   6#include <linux/module.h>
   7#include <linux/fs.h>
   8#include <linux/msdos_fs.h>
   9#include <linux/blkdev.h>
  10#include "fat.h"
  11
  12struct fatent_operations {
  13        void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
  14        void (*ent_set_ptr)(struct fat_entry *, int);
  15        int (*ent_bread)(struct super_block *, struct fat_entry *,
  16                         int, sector_t);
  17        int (*ent_get)(struct fat_entry *);
  18        void (*ent_put)(struct fat_entry *, int);
  19        int (*ent_next)(struct fat_entry *);
  20};
  21
  22static DEFINE_SPINLOCK(fat12_entry_lock);
  23
  24static void fat12_ent_blocknr(struct super_block *sb, int entry,
  25                              int *offset, sector_t *blocknr)
  26{
  27        struct msdos_sb_info *sbi = MSDOS_SB(sb);
  28        int bytes = entry + (entry >> 1);
  29        WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
  30        *offset = bytes & (sb->s_blocksize - 1);
  31        *blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
  32}
  33
  34static void fat_ent_blocknr(struct super_block *sb, int entry,
  35                            int *offset, sector_t *blocknr)
  36{
  37        struct msdos_sb_info *sbi = MSDOS_SB(sb);
  38        int bytes = (entry << sbi->fatent_shift);
  39        WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
  40        *offset = bytes & (sb->s_blocksize - 1);
  41        *blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
  42}
  43
  44static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
  45{
  46        struct buffer_head **bhs = fatent->bhs;
  47        if (fatent->nr_bhs == 1) {
  48                WARN_ON(offset >= (bhs[0]->b_size - 1));
  49                fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
  50                fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
  51        } else {
  52                WARN_ON(offset != (bhs[0]->b_size - 1));
  53                fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
  54                fatent->u.ent12_p[1] = bhs[1]->b_data;
  55        }
  56}
  57
  58static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
  59{
  60        WARN_ON(offset & (2 - 1));
  61        fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
  62}
  63
  64static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
  65{
  66        WARN_ON(offset & (4 - 1));
  67        fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
  68}
  69
  70static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
  71                           int offset, sector_t blocknr)
  72{
  73        struct buffer_head **bhs = fatent->bhs;
  74
  75        WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
  76        fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
  77
  78        bhs[0] = sb_bread(sb, blocknr);
  79        if (!bhs[0])
  80                goto err;
  81
  82        if ((offset + 1) < sb->s_blocksize)
  83                fatent->nr_bhs = 1;
  84        else {
  85                /* This entry is block boundary, it needs the next block */
  86                blocknr++;
  87                bhs[1] = sb_bread(sb, blocknr);
  88                if (!bhs[1])
  89                        goto err_brelse;
  90                fatent->nr_bhs = 2;
  91        }
  92        fat12_ent_set_ptr(fatent, offset);
  93        return 0;
  94
  95err_brelse:
  96        brelse(bhs[0]);
  97err:
  98        fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)", (llu)blocknr);
  99        return -EIO;
 100}
 101
 102static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
 103                         int offset, sector_t blocknr)
 104{
 105        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 106
 107        WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
 108        fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
 109        fatent->bhs[0] = sb_bread(sb, blocknr);
 110        if (!fatent->bhs[0]) {
 111                fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
 112                       (llu)blocknr);
 113                return -EIO;
 114        }
 115        fatent->nr_bhs = 1;
 116        ops->ent_set_ptr(fatent, offset);
 117        return 0;
 118}
 119
 120static int fat12_ent_get(struct fat_entry *fatent)
 121{
 122        u8 **ent12_p = fatent->u.ent12_p;
 123        int next;
 124
 125        spin_lock(&fat12_entry_lock);
 126        if (fatent->entry & 1)
 127                next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
 128        else
 129                next = (*ent12_p[1] << 8) | *ent12_p[0];
 130        spin_unlock(&fat12_entry_lock);
 131
 132        next &= 0x0fff;
 133        if (next >= BAD_FAT12)
 134                next = FAT_ENT_EOF;
 135        return next;
 136}
 137
 138static int fat16_ent_get(struct fat_entry *fatent)
 139{
 140        int next = le16_to_cpu(*fatent->u.ent16_p);
 141        WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
 142        if (next >= BAD_FAT16)
 143                next = FAT_ENT_EOF;
 144        return next;
 145}
 146
 147static int fat32_ent_get(struct fat_entry *fatent)
 148{
 149        int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
 150        WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
 151        if (next >= BAD_FAT32)
 152                next = FAT_ENT_EOF;
 153        return next;
 154}
 155
 156static void fat12_ent_put(struct fat_entry *fatent, int new)
 157{
 158        u8 **ent12_p = fatent->u.ent12_p;
 159
 160        if (new == FAT_ENT_EOF)
 161                new = EOF_FAT12;
 162
 163        spin_lock(&fat12_entry_lock);
 164        if (fatent->entry & 1) {
 165                *ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
 166                *ent12_p[1] = new >> 4;
 167        } else {
 168                *ent12_p[0] = new & 0xff;
 169                *ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
 170        }
 171        spin_unlock(&fat12_entry_lock);
 172
 173        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
 174        if (fatent->nr_bhs == 2)
 175                mark_buffer_dirty_inode(fatent->bhs[1], fatent->fat_inode);
 176}
 177
 178static void fat16_ent_put(struct fat_entry *fatent, int new)
 179{
 180        if (new == FAT_ENT_EOF)
 181                new = EOF_FAT16;
 182
 183        *fatent->u.ent16_p = cpu_to_le16(new);
 184        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
 185}
 186
 187static void fat32_ent_put(struct fat_entry *fatent, int new)
 188{
 189        WARN_ON(new & 0xf0000000);
 190        new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
 191        *fatent->u.ent32_p = cpu_to_le32(new);
 192        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
 193}
 194
 195static int fat12_ent_next(struct fat_entry *fatent)
 196{
 197        u8 **ent12_p = fatent->u.ent12_p;
 198        struct buffer_head **bhs = fatent->bhs;
 199        u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
 200
 201        fatent->entry++;
 202        if (fatent->nr_bhs == 1) {
 203                WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data +
 204                                                        (bhs[0]->b_size - 2)));
 205                WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data +
 206                                                        (bhs[0]->b_size - 1)));
 207                if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
 208                        ent12_p[0] = nextp - 1;
 209                        ent12_p[1] = nextp;
 210                        return 1;
 211                }
 212        } else {
 213                WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data +
 214                                                        (bhs[0]->b_size - 1)));
 215                WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
 216                ent12_p[0] = nextp - 1;
 217                ent12_p[1] = nextp;
 218                brelse(bhs[0]);
 219                bhs[0] = bhs[1];
 220                fatent->nr_bhs = 1;
 221                return 1;
 222        }
 223        ent12_p[0] = NULL;
 224        ent12_p[1] = NULL;
 225        return 0;
 226}
 227
 228static int fat16_ent_next(struct fat_entry *fatent)
 229{
 230        const struct buffer_head *bh = fatent->bhs[0];
 231        fatent->entry++;
 232        if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
 233                fatent->u.ent16_p++;
 234                return 1;
 235        }
 236        fatent->u.ent16_p = NULL;
 237        return 0;
 238}
 239
 240static int fat32_ent_next(struct fat_entry *fatent)
 241{
 242        const struct buffer_head *bh = fatent->bhs[0];
 243        fatent->entry++;
 244        if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
 245                fatent->u.ent32_p++;
 246                return 1;
 247        }
 248        fatent->u.ent32_p = NULL;
 249        return 0;
 250}
 251
 252static struct fatent_operations fat12_ops = {
 253        .ent_blocknr    = fat12_ent_blocknr,
 254        .ent_set_ptr    = fat12_ent_set_ptr,
 255        .ent_bread      = fat12_ent_bread,
 256        .ent_get        = fat12_ent_get,
 257        .ent_put        = fat12_ent_put,
 258        .ent_next       = fat12_ent_next,
 259};
 260
 261static struct fatent_operations fat16_ops = {
 262        .ent_blocknr    = fat_ent_blocknr,
 263        .ent_set_ptr    = fat16_ent_set_ptr,
 264        .ent_bread      = fat_ent_bread,
 265        .ent_get        = fat16_ent_get,
 266        .ent_put        = fat16_ent_put,
 267        .ent_next       = fat16_ent_next,
 268};
 269
 270static struct fatent_operations fat32_ops = {
 271        .ent_blocknr    = fat_ent_blocknr,
 272        .ent_set_ptr    = fat32_ent_set_ptr,
 273        .ent_bread      = fat_ent_bread,
 274        .ent_get        = fat32_ent_get,
 275        .ent_put        = fat32_ent_put,
 276        .ent_next       = fat32_ent_next,
 277};
 278
 279static inline void lock_fat(struct msdos_sb_info *sbi)
 280{
 281        mutex_lock(&sbi->fat_lock);
 282}
 283
 284static inline void unlock_fat(struct msdos_sb_info *sbi)
 285{
 286        mutex_unlock(&sbi->fat_lock);
 287}
 288
 289void fat_ent_access_init(struct super_block *sb)
 290{
 291        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 292
 293        mutex_init(&sbi->fat_lock);
 294
 295        switch (sbi->fat_bits) {
 296        case 32:
 297                sbi->fatent_shift = 2;
 298                sbi->fatent_ops = &fat32_ops;
 299                break;
 300        case 16:
 301                sbi->fatent_shift = 1;
 302                sbi->fatent_ops = &fat16_ops;
 303                break;
 304        case 12:
 305                sbi->fatent_shift = -1;
 306                sbi->fatent_ops = &fat12_ops;
 307                break;
 308        }
 309}
 310
 311static void mark_fsinfo_dirty(struct super_block *sb)
 312{
 313        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 314
 315        if (sb->s_flags & MS_RDONLY || sbi->fat_bits != 32)
 316                return;
 317
 318        __mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
 319}
 320
 321static inline int fat_ent_update_ptr(struct super_block *sb,
 322                                     struct fat_entry *fatent,
 323                                     int offset, sector_t blocknr)
 324{
 325        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 326        struct fatent_operations *ops = sbi->fatent_ops;
 327        struct buffer_head **bhs = fatent->bhs;
 328
 329        /* Is this fatent's blocks including this entry? */
 330        if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
 331                return 0;
 332        if (sbi->fat_bits == 12) {
 333                if ((offset + 1) < sb->s_blocksize) {
 334                        /* This entry is on bhs[0]. */
 335                        if (fatent->nr_bhs == 2) {
 336                                brelse(bhs[1]);
 337                                fatent->nr_bhs = 1;
 338                        }
 339                } else {
 340                        /* This entry needs the next block. */
 341                        if (fatent->nr_bhs != 2)
 342                                return 0;
 343                        if (bhs[1]->b_blocknr != (blocknr + 1))
 344                                return 0;
 345                }
 346        }
 347        ops->ent_set_ptr(fatent, offset);
 348        return 1;
 349}
 350
 351int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
 352{
 353        struct super_block *sb = inode->i_sb;
 354        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
 355        struct fatent_operations *ops = sbi->fatent_ops;
 356        int err, offset;
 357        sector_t blocknr;
 358
 359        if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
 360                fatent_brelse(fatent);
 361                fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
 362                return -EIO;
 363        }
 364
 365        fatent_set_entry(fatent, entry);
 366        ops->ent_blocknr(sb, entry, &offset, &blocknr);
 367
 368        if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
 369                fatent_brelse(fatent);
 370                err = ops->ent_bread(sb, fatent, offset, blocknr);
 371                if (err)
 372                        return err;
 373        }
 374        return ops->ent_get(fatent);
 375}
 376
 377/* FIXME: We can write the blocks as more big chunk. */
 378static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
 379                          int nr_bhs)
 380{
 381        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 382        struct buffer_head *c_bh;
 383        int err, n, copy;
 384
 385        err = 0;
 386        for (copy = 1; copy < sbi->fats; copy++) {
 387                sector_t backup_fat = sbi->fat_length * copy;
 388
 389                for (n = 0; n < nr_bhs; n++) {
 390                        c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
 391                        if (!c_bh) {
 392                                err = -ENOMEM;
 393                                goto error;
 394                        }
 395                        memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
 396                        set_buffer_uptodate(c_bh);
 397                        mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
 398                        if (sb->s_flags & MS_SYNCHRONOUS)
 399                                err = sync_dirty_buffer(c_bh);
 400                        brelse(c_bh);
 401                        if (err)
 402                                goto error;
 403                }
 404        }
 405error:
 406        return err;
 407}
 408
 409int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
 410                  int new, int wait)
 411{
 412        struct super_block *sb = inode->i_sb;
 413        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 414        int err;
 415
 416        ops->ent_put(fatent, new);
 417        if (wait) {
 418                err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
 419                if (err)
 420                        return err;
 421        }
 422        return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
 423}
 424
 425static inline int fat_ent_next(struct msdos_sb_info *sbi,
 426                               struct fat_entry *fatent)
 427{
 428        if (sbi->fatent_ops->ent_next(fatent)) {
 429                if (fatent->entry < sbi->max_cluster)
 430                        return 1;
 431        }
 432        return 0;
 433}
 434
 435static inline int fat_ent_read_block(struct super_block *sb,
 436                                     struct fat_entry *fatent)
 437{
 438        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 439        sector_t blocknr;
 440        int offset;
 441
 442        fatent_brelse(fatent);
 443        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 444        return ops->ent_bread(sb, fatent, offset, blocknr);
 445}
 446
 447static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
 448                            struct fat_entry *fatent)
 449{
 450        int n, i;
 451
 452        for (n = 0; n < fatent->nr_bhs; n++) {
 453                for (i = 0; i < *nr_bhs; i++) {
 454                        if (fatent->bhs[n] == bhs[i])
 455                                break;
 456                }
 457                if (i == *nr_bhs) {
 458                        get_bh(fatent->bhs[n]);
 459                        bhs[i] = fatent->bhs[n];
 460                        (*nr_bhs)++;
 461                }
 462        }
 463}
 464
 465int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
 466{
 467        struct super_block *sb = inode->i_sb;
 468        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 469        struct fatent_operations *ops = sbi->fatent_ops;
 470        struct fat_entry fatent, prev_ent;
 471        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 472        int i, count, err, nr_bhs, idx_clus;
 473
 474        BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));    /* fixed limit */
 475
 476        lock_fat(sbi);
 477        if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
 478            sbi->free_clusters < nr_cluster) {
 479                unlock_fat(sbi);
 480                return -ENOSPC;
 481        }
 482
 483        err = nr_bhs = idx_clus = 0;
 484        count = FAT_START_ENT;
 485        fatent_init(&prev_ent);
 486        fatent_init(&fatent);
 487        fatent_set_entry(&fatent, sbi->prev_free + 1);
 488        while (count < sbi->max_cluster) {
 489                if (fatent.entry >= sbi->max_cluster)
 490                        fatent.entry = FAT_START_ENT;
 491                fatent_set_entry(&fatent, fatent.entry);
 492                err = fat_ent_read_block(sb, &fatent);
 493                if (err)
 494                        goto out;
 495
 496                /* Find the free entries in a block */
 497                do {
 498                        if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
 499                                int entry = fatent.entry;
 500
 501                                /* make the cluster chain */
 502                                ops->ent_put(&fatent, FAT_ENT_EOF);
 503                                if (prev_ent.nr_bhs)
 504                                        ops->ent_put(&prev_ent, entry);
 505
 506                                fat_collect_bhs(bhs, &nr_bhs, &fatent);
 507
 508                                sbi->prev_free = entry;
 509                                if (sbi->free_clusters != -1)
 510                                        sbi->free_clusters--;
 511
 512                                cluster[idx_clus] = entry;
 513                                idx_clus++;
 514                                if (idx_clus == nr_cluster)
 515                                        goto out;
 516
 517                                /*
 518                                 * fat_collect_bhs() gets ref-count of bhs,
 519                                 * so we can still use the prev_ent.
 520                                 */
 521                                prev_ent = fatent;
 522                        }
 523                        count++;
 524                        if (count == sbi->max_cluster)
 525                                break;
 526                } while (fat_ent_next(sbi, &fatent));
 527        }
 528
 529        /* Couldn't allocate the free entries */
 530        sbi->free_clusters = 0;
 531        sbi->free_clus_valid = 1;
 532        err = -ENOSPC;
 533
 534out:
 535        unlock_fat(sbi);
 536        mark_fsinfo_dirty(sb);
 537        fatent_brelse(&fatent);
 538        if (!err) {
 539                if (inode_needs_sync(inode))
 540                        err = fat_sync_bhs(bhs, nr_bhs);
 541                if (!err)
 542                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 543        }
 544        for (i = 0; i < nr_bhs; i++)
 545                brelse(bhs[i]);
 546
 547        if (err && idx_clus)
 548                fat_free_clusters(inode, cluster[0]);
 549
 550        return err;
 551}
 552
 553int fat_free_clusters(struct inode *inode, int cluster)
 554{
 555        struct super_block *sb = inode->i_sb;
 556        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 557        struct fatent_operations *ops = sbi->fatent_ops;
 558        struct fat_entry fatent;
 559        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 560        int i, err, nr_bhs;
 561        int first_cl = cluster, dirty_fsinfo = 0;
 562
 563        nr_bhs = 0;
 564        fatent_init(&fatent);
 565        lock_fat(sbi);
 566        do {
 567                cluster = fat_ent_read(inode, &fatent, cluster);
 568                if (cluster < 0) {
 569                        err = cluster;
 570                        goto error;
 571                } else if (cluster == FAT_ENT_FREE) {
 572                        fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
 573                                     __func__);
 574                        err = -EIO;
 575                        goto error;
 576                }
 577
 578                if (sbi->options.discard) {
 579                        /*
 580                         * Issue discard for the sectors we no longer
 581                         * care about, batching contiguous clusters
 582                         * into one request
 583                         */
 584                        if (cluster != fatent.entry + 1) {
 585                                int nr_clus = fatent.entry - first_cl + 1;
 586
 587                                sb_issue_discard(sb,
 588                                        fat_clus_to_blknr(sbi, first_cl),
 589                                        nr_clus * sbi->sec_per_clus,
 590                                        GFP_NOFS, 0);
 591
 592                                first_cl = cluster;
 593                        }
 594                }
 595
 596                ops->ent_put(&fatent, FAT_ENT_FREE);
 597                if (sbi->free_clusters != -1) {
 598                        sbi->free_clusters++;
 599                        dirty_fsinfo = 1;
 600                }
 601
 602                if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
 603                        if (sb->s_flags & MS_SYNCHRONOUS) {
 604                                err = fat_sync_bhs(bhs, nr_bhs);
 605                                if (err)
 606                                        goto error;
 607                        }
 608                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 609                        if (err)
 610                                goto error;
 611                        for (i = 0; i < nr_bhs; i++)
 612                                brelse(bhs[i]);
 613                        nr_bhs = 0;
 614                }
 615                fat_collect_bhs(bhs, &nr_bhs, &fatent);
 616        } while (cluster != FAT_ENT_EOF);
 617
 618        if (sb->s_flags & MS_SYNCHRONOUS) {
 619                err = fat_sync_bhs(bhs, nr_bhs);
 620                if (err)
 621                        goto error;
 622        }
 623        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 624error:
 625        fatent_brelse(&fatent);
 626        for (i = 0; i < nr_bhs; i++)
 627                brelse(bhs[i]);
 628        unlock_fat(sbi);
 629        if (dirty_fsinfo)
 630                mark_fsinfo_dirty(sb);
 631
 632        return err;
 633}
 634EXPORT_SYMBOL_GPL(fat_free_clusters);
 635
 636/* 128kb is the whole sectors for FAT12 and FAT16 */
 637#define FAT_READA_SIZE          (128 * 1024)
 638
 639static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
 640                          unsigned long reada_blocks)
 641{
 642        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 643        sector_t blocknr;
 644        int i, offset;
 645
 646        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 647
 648        for (i = 0; i < reada_blocks; i++)
 649                sb_breadahead(sb, blocknr + i);
 650}
 651
 652int fat_count_free_clusters(struct super_block *sb)
 653{
 654        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 655        struct fatent_operations *ops = sbi->fatent_ops;
 656        struct fat_entry fatent;
 657        unsigned long reada_blocks, reada_mask, cur_block;
 658        int err = 0, free;
 659
 660        lock_fat(sbi);
 661        if (sbi->free_clusters != -1 && sbi->free_clus_valid)
 662                goto out;
 663
 664        reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
 665        reada_mask = reada_blocks - 1;
 666        cur_block = 0;
 667
 668        free = 0;
 669        fatent_init(&fatent);
 670        fatent_set_entry(&fatent, FAT_START_ENT);
 671        while (fatent.entry < sbi->max_cluster) {
 672                /* readahead of fat blocks */
 673                if ((cur_block & reada_mask) == 0) {
 674                        unsigned long rest = sbi->fat_length - cur_block;
 675                        fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
 676                }
 677                cur_block++;
 678
 679                err = fat_ent_read_block(sb, &fatent);
 680                if (err)
 681                        goto out;
 682
 683                do {
 684                        if (ops->ent_get(&fatent) == FAT_ENT_FREE)
 685                                free++;
 686                } while (fat_ent_next(sbi, &fatent));
 687        }
 688        sbi->free_clusters = free;
 689        sbi->free_clus_valid = 1;
 690        mark_fsinfo_dirty(sb);
 691        fatent_brelse(&fatent);
 692out:
 693        unlock_fat(sbi);
 694        return err;
 695}
 696
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