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        if (new == FAT_ENT_EOF)
 190                new = EOF_FAT32;
 191
 192        WARN_ON(new & 0xf0000000);
 193        new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
 194        *fatent->u.ent32_p = cpu_to_le32(new);
 195        mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
 196}
 197
 198static int fat12_ent_next(struct fat_entry *fatent)
 199{
 200        u8 **ent12_p = fatent->u.ent12_p;
 201        struct buffer_head **bhs = fatent->bhs;
 202        u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
 203
 204        fatent->entry++;
 205        if (fatent->nr_bhs == 1) {
 206                WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 2)));
 207                WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
 208                if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
 209                        ent12_p[0] = nextp - 1;
 210                        ent12_p[1] = nextp;
 211                        return 1;
 212                }
 213        } else {
 214                WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data + (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 inline int fat_ent_update_ptr(struct super_block *sb,
 312                                     struct fat_entry *fatent,
 313                                     int offset, sector_t blocknr)
 314{
 315        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 316        struct fatent_operations *ops = sbi->fatent_ops;
 317        struct buffer_head **bhs = fatent->bhs;
 318
 319        /* Is this fatent's blocks including this entry? */
 320        if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
 321                return 0;
 322        if (sbi->fat_bits == 12) {
 323                if ((offset + 1) < sb->s_blocksize) {
 324                        /* This entry is on bhs[0]. */
 325                        if (fatent->nr_bhs == 2) {
 326                                brelse(bhs[1]);
 327                                fatent->nr_bhs = 1;
 328                        }
 329                } else {
 330                        /* This entry needs the next block. */
 331                        if (fatent->nr_bhs != 2)
 332                                return 0;
 333                        if (bhs[1]->b_blocknr != (blocknr + 1))
 334                                return 0;
 335                }
 336        }
 337        ops->ent_set_ptr(fatent, offset);
 338        return 1;
 339}
 340
 341int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
 342{
 343        struct super_block *sb = inode->i_sb;
 344        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
 345        struct fatent_operations *ops = sbi->fatent_ops;
 346        int err, offset;
 347        sector_t blocknr;
 348
 349        if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
 350                fatent_brelse(fatent);
 351                fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
 352                return -EIO;
 353        }
 354
 355        fatent_set_entry(fatent, entry);
 356        ops->ent_blocknr(sb, entry, &offset, &blocknr);
 357
 358        if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
 359                fatent_brelse(fatent);
 360                err = ops->ent_bread(sb, fatent, offset, blocknr);
 361                if (err)
 362                        return err;
 363        }
 364        return ops->ent_get(fatent);
 365}
 366
 367/* FIXME: We can write the blocks as more big chunk. */
 368static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
 369                          int nr_bhs)
 370{
 371        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 372        struct buffer_head *c_bh;
 373        int err, n, copy;
 374
 375        err = 0;
 376        for (copy = 1; copy < sbi->fats; copy++) {
 377                sector_t backup_fat = sbi->fat_length * copy;
 378
 379                for (n = 0; n < nr_bhs; n++) {
 380                        c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
 381                        if (!c_bh) {
 382                                err = -ENOMEM;
 383                                goto error;
 384                        }
 385                        memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
 386                        set_buffer_uptodate(c_bh);
 387                        mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
 388                        if (sb->s_flags & MS_SYNCHRONOUS)
 389                                err = sync_dirty_buffer(c_bh);
 390                        brelse(c_bh);
 391                        if (err)
 392                                goto error;
 393                }
 394        }
 395error:
 396        return err;
 397}
 398
 399int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
 400                  int new, int wait)
 401{
 402        struct super_block *sb = inode->i_sb;
 403        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 404        int err;
 405
 406        ops->ent_put(fatent, new);
 407        if (wait) {
 408                err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
 409                if (err)
 410                        return err;
 411        }
 412        return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
 413}
 414
 415static inline int fat_ent_next(struct msdos_sb_info *sbi,
 416                               struct fat_entry *fatent)
 417{
 418        if (sbi->fatent_ops->ent_next(fatent)) {
 419                if (fatent->entry < sbi->max_cluster)
 420                        return 1;
 421        }
 422        return 0;
 423}
 424
 425static inline int fat_ent_read_block(struct super_block *sb,
 426                                     struct fat_entry *fatent)
 427{
 428        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 429        sector_t blocknr;
 430        int offset;
 431
 432        fatent_brelse(fatent);
 433        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 434        return ops->ent_bread(sb, fatent, offset, blocknr);
 435}
 436
 437static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
 438                            struct fat_entry *fatent)
 439{
 440        int n, i;
 441
 442        for (n = 0; n < fatent->nr_bhs; n++) {
 443                for (i = 0; i < *nr_bhs; i++) {
 444                        if (fatent->bhs[n] == bhs[i])
 445                                break;
 446                }
 447                if (i == *nr_bhs) {
 448                        get_bh(fatent->bhs[n]);
 449                        bhs[i] = fatent->bhs[n];
 450                        (*nr_bhs)++;
 451                }
 452        }
 453}
 454
 455int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
 456{
 457        struct super_block *sb = inode->i_sb;
 458        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 459        struct fatent_operations *ops = sbi->fatent_ops;
 460        struct fat_entry fatent, prev_ent;
 461        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 462        int i, count, err, nr_bhs, idx_clus;
 463
 464        BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));    /* fixed limit */
 465
 466        lock_fat(sbi);
 467        if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
 468            sbi->free_clusters < nr_cluster) {
 469                unlock_fat(sbi);
 470                return -ENOSPC;
 471        }
 472
 473        err = nr_bhs = idx_clus = 0;
 474        count = FAT_START_ENT;
 475        fatent_init(&prev_ent);
 476        fatent_init(&fatent);
 477        fatent_set_entry(&fatent, sbi->prev_free + 1);
 478        while (count < sbi->max_cluster) {
 479                if (fatent.entry >= sbi->max_cluster)
 480                        fatent.entry = FAT_START_ENT;
 481                fatent_set_entry(&fatent, fatent.entry);
 482                err = fat_ent_read_block(sb, &fatent);
 483                if (err)
 484                        goto out;
 485
 486                /* Find the free entries in a block */
 487                do {
 488                        if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
 489                                int entry = fatent.entry;
 490
 491                                /* make the cluster chain */
 492                                ops->ent_put(&fatent, FAT_ENT_EOF);
 493                                if (prev_ent.nr_bhs)
 494                                        ops->ent_put(&prev_ent, entry);
 495
 496                                fat_collect_bhs(bhs, &nr_bhs, &fatent);
 497
 498                                sbi->prev_free = entry;
 499                                if (sbi->free_clusters != -1)
 500                                        sbi->free_clusters--;
 501                                sb->s_dirt = 1;
 502
 503                                cluster[idx_clus] = entry;
 504                                idx_clus++;
 505                                if (idx_clus == nr_cluster)
 506                                        goto out;
 507
 508                                /*
 509                                 * fat_collect_bhs() gets ref-count of bhs,
 510                                 * so we can still use the prev_ent.
 511                                 */
 512                                prev_ent = fatent;
 513                        }
 514                        count++;
 515                        if (count == sbi->max_cluster)
 516                                break;
 517                } while (fat_ent_next(sbi, &fatent));
 518        }
 519
 520        /* Couldn't allocate the free entries */
 521        sbi->free_clusters = 0;
 522        sbi->free_clus_valid = 1;
 523        sb->s_dirt = 1;
 524        err = -ENOSPC;
 525
 526out:
 527        unlock_fat(sbi);
 528        fatent_brelse(&fatent);
 529        if (!err) {
 530                if (inode_needs_sync(inode))
 531                        err = fat_sync_bhs(bhs, nr_bhs);
 532                if (!err)
 533                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 534        }
 535        for (i = 0; i < nr_bhs; i++)
 536                brelse(bhs[i]);
 537
 538        if (err && idx_clus)
 539                fat_free_clusters(inode, cluster[0]);
 540
 541        return err;
 542}
 543
 544int fat_free_clusters(struct inode *inode, int cluster)
 545{
 546        struct super_block *sb = inode->i_sb;
 547        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 548        struct fatent_operations *ops = sbi->fatent_ops;
 549        struct fat_entry fatent;
 550        struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 551        int i, err, nr_bhs;
 552        int first_cl = cluster;
 553
 554        nr_bhs = 0;
 555        fatent_init(&fatent);
 556        lock_fat(sbi);
 557        do {
 558                cluster = fat_ent_read(inode, &fatent, cluster);
 559                if (cluster < 0) {
 560                        err = cluster;
 561                        goto error;
 562                } else if (cluster == FAT_ENT_FREE) {
 563                        fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
 564                                     __func__);
 565                        err = -EIO;
 566                        goto error;
 567                }
 568
 569                if (sbi->options.discard) {
 570                        /*
 571                         * Issue discard for the sectors we no longer
 572                         * care about, batching contiguous clusters
 573                         * into one request
 574                         */
 575                        if (cluster != fatent.entry + 1) {
 576                                int nr_clus = fatent.entry - first_cl + 1;
 577
 578                                sb_issue_discard(sb,
 579                                        fat_clus_to_blknr(sbi, first_cl),
 580                                        nr_clus * sbi->sec_per_clus,
 581                                        GFP_NOFS, 0);
 582
 583                                first_cl = cluster;
 584                        }
 585                }
 586
 587                ops->ent_put(&fatent, FAT_ENT_FREE);
 588                if (sbi->free_clusters != -1) {
 589                        sbi->free_clusters++;
 590                        sb->s_dirt = 1;
 591                }
 592
 593                if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
 594                        if (sb->s_flags & MS_SYNCHRONOUS) {
 595                                err = fat_sync_bhs(bhs, nr_bhs);
 596                                if (err)
 597                                        goto error;
 598                        }
 599                        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 600                        if (err)
 601                                goto error;
 602                        for (i = 0; i < nr_bhs; i++)
 603                                brelse(bhs[i]);
 604                        nr_bhs = 0;
 605                }
 606                fat_collect_bhs(bhs, &nr_bhs, &fatent);
 607        } while (cluster != FAT_ENT_EOF);
 608
 609        if (sb->s_flags & MS_SYNCHRONOUS) {
 610                err = fat_sync_bhs(bhs, nr_bhs);
 611                if (err)
 612                        goto error;
 613        }
 614        err = fat_mirror_bhs(sb, bhs, nr_bhs);
 615error:
 616        fatent_brelse(&fatent);
 617        for (i = 0; i < nr_bhs; i++)
 618                brelse(bhs[i]);
 619        unlock_fat(sbi);
 620
 621        return err;
 622}
 623
 624EXPORT_SYMBOL_GPL(fat_free_clusters);
 625
 626/* 128kb is the whole sectors for FAT12 and FAT16 */
 627#define FAT_READA_SIZE          (128 * 1024)
 628
 629static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
 630                          unsigned long reada_blocks)
 631{
 632        struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 633        sector_t blocknr;
 634        int i, offset;
 635
 636        ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 637
 638        for (i = 0; i < reada_blocks; i++)
 639                sb_breadahead(sb, blocknr + i);
 640}
 641
 642int fat_count_free_clusters(struct super_block *sb)
 643{
 644        struct msdos_sb_info *sbi = MSDOS_SB(sb);
 645        struct fatent_operations *ops = sbi->fatent_ops;
 646        struct fat_entry fatent;
 647        unsigned long reada_blocks, reada_mask, cur_block;
 648        int err = 0, free;
 649
 650        lock_fat(sbi);
 651        if (sbi->free_clusters != -1 && sbi->free_clus_valid)
 652                goto out;
 653
 654        reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
 655        reada_mask = reada_blocks - 1;
 656        cur_block = 0;
 657
 658        free = 0;
 659        fatent_init(&fatent);
 660        fatent_set_entry(&fatent, FAT_START_ENT);
 661        while (fatent.entry < sbi->max_cluster) {
 662                /* readahead of fat blocks */
 663                if ((cur_block & reada_mask) == 0) {
 664                        unsigned long rest = sbi->fat_length - cur_block;
 665                        fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
 666                }
 667                cur_block++;
 668
 669                err = fat_ent_read_block(sb, &fatent);
 670                if (err)
 671                        goto out;
 672
 673                do {
 674                        if (ops->ent_get(&fatent) == FAT_ENT_FREE)
 675                                free++;
 676                } while (fat_ent_next(sbi, &fatent));
 677        }
 678        sbi->free_clusters = free;
 679        sbi->free_clus_valid = 1;
 680        sb->s_dirt = 1;
 681        fatent_brelse(&fatent);
 682out:
 683        unlock_fat(sbi);
 684        return err;
 685}
 686