fs/fat/fatent.c

   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
  12 struct 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
  22 static DEFINE_SPINLOCK(fat12_entry_lock);
  23
  24 static 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
  34 static 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
  44 static 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
  58 static 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
  64 static 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
  70 static 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         bhs[0] = sb_bread(sb, blocknr);
  77         if (!bhs[0])
  78                 goto err;
  79
  80         if ((offset + 1) < sb->s_blocksize)
  81                 fatent->nr_bhs = 1;
  82         else {
  83                 /* This entry is block boundary, it needs the next block */
  84                 blocknr++;
  85                 bhs[1] = sb_bread(sb, blocknr);
  86                 if (!bhs[1])
  87                         goto err_brelse;
  88                 fatent->nr_bhs = 2;
  89         }
  90         fat12_ent_set_ptr(fatent, offset);
  91         return 0;
  92
  93 err_brelse:
  94         brelse(bhs[0]);
  95 err:
  96         printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
  97                (unsigned long long)blocknr);
  98         return -EIO;
  99 }
 100
 101 static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
 102                          int offset, sector_t blocknr)
 103 {
 104         struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 105
 106         WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
 107         fatent->bhs[0] = sb_bread(sb, blocknr);
 108         if (!fatent->bhs[0]) {
 109                 printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
 110                        (unsigned long long)blocknr);
 111                 return -EIO;
 112         }
 113         fatent->nr_bhs = 1;
 114         ops->ent_set_ptr(fatent, offset);
 115         return 0;
 116 }
 117
 118 static int fat12_ent_get(struct fat_entry *fatent)
 119 {
 120         u8 **ent12_p = fatent->u.ent12_p;
 121         int next;
 122
 123         spin_lock(&fat12_entry_lock);
 124         if (fatent->entry & 1)
 125                 next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
 126         else
 127                 next = (*ent12_p[1] << 8) | *ent12_p[0];
 128         spin_unlock(&fat12_entry_lock);
 129
 130         next &= 0x0fff;
 131         if (next >= BAD_FAT12)
 132                 next = FAT_ENT_EOF;
 133         return next;
 134 }
 135
 136 static int fat16_ent_get(struct fat_entry *fatent)
 137 {
 138         int next = le16_to_cpu(*fatent->u.ent16_p);
 139         WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
 140         if (next >= BAD_FAT16)
 141                 next = FAT_ENT_EOF;
 142         return next;
 143 }
 144
 145 static int fat32_ent_get(struct fat_entry *fatent)
 146 {
 147         int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
 148         WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
 149         if (next >= BAD_FAT32)
 150                 next = FAT_ENT_EOF;
 151         return next;
 152 }
 153
 154 static void fat12_ent_put(struct fat_entry *fatent, int new)
 155 {
 156         u8 **ent12_p = fatent->u.ent12_p;
 157
 158         if (new == FAT_ENT_EOF)
 159                 new = EOF_FAT12;
 160
 161         spin_lock(&fat12_entry_lock);
 162         if (fatent->entry & 1) {
 163                 *ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
 164                 *ent12_p[1] = new >> 4;
 165         } else {
 166                 *ent12_p[0] = new & 0xff;
 167                 *ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
 168         }
 169         spin_unlock(&fat12_entry_lock);
 170
 171         mark_buffer_dirty(fatent->bhs[0]);
 172         if (fatent->nr_bhs == 2)
 173                 mark_buffer_dirty(fatent->bhs[1]);
 174 }
 175
 176 static void fat16_ent_put(struct fat_entry *fatent, int new)
 177 {
 178         if (new == FAT_ENT_EOF)
 179                 new = EOF_FAT16;
 180
 181         *fatent->u.ent16_p = cpu_to_le16(new);
 182         mark_buffer_dirty(fatent->bhs[0]);
 183 }
 184
 185 static void fat32_ent_put(struct fat_entry *fatent, int new)
 186 {
 187         if (new == FAT_ENT_EOF)
 188                 new = EOF_FAT32;
 189
 190         WARN_ON(new & 0xf0000000);
 191         new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
 192         *fatent->u.ent32_p = cpu_to_le32(new);
 193         mark_buffer_dirty(fatent->bhs[0]);
 194 }
 195
 196 static int fat12_ent_next(struct fat_entry *fatent)
 197 {
 198         u8 **ent12_p = fatent->u.ent12_p;
 199         struct buffer_head **bhs = fatent->bhs;
 200         u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
 201
 202         fatent->entry++;
 203         if (fatent->nr_bhs == 1) {
 204                 WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 2)));
 205                 WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
 206                 if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
 207                         ent12_p[0] = nextp - 1;
 208                         ent12_p[1] = nextp;
 209                         return 1;
 210                 }
 211         } else {
 212                 WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
 213                 WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
 214                 ent12_p[0] = nextp - 1;
 215                 ent12_p[1] = nextp;
 216                 brelse(bhs[0]);
 217                 bhs[0] = bhs[1];
 218                 fatent->nr_bhs = 1;
 219                 return 1;
 220         }
 221         ent12_p[0] = NULL;
 222         ent12_p[1] = NULL;
 223         return 0;
 224 }
 225
 226 static int fat16_ent_next(struct fat_entry *fatent)
 227 {
 228         const struct buffer_head *bh = fatent->bhs[0];
 229         fatent->entry++;
 230         if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
 231                 fatent->u.ent16_p++;
 232                 return 1;
 233         }
 234         fatent->u.ent16_p = NULL;
 235         return 0;
 236 }
 237
 238 static int fat32_ent_next(struct fat_entry *fatent)
 239 {
 240         const struct buffer_head *bh = fatent->bhs[0];
 241         fatent->entry++;
 242         if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
 243                 fatent->u.ent32_p++;
 244                 return 1;
 245         }
 246         fatent->u.ent32_p = NULL;
 247         return 0;
 248 }
 249
 250 static struct fatent_operations fat12_ops = {
 251         .ent_blocknr    = fat12_ent_blocknr,
 252         .ent_set_ptr    = fat12_ent_set_ptr,
 253         .ent_bread      = fat12_ent_bread,
 254         .ent_get        = fat12_ent_get,
 255         .ent_put        = fat12_ent_put,
 256         .ent_next       = fat12_ent_next,
 257 };
 258
 259 static struct fatent_operations fat16_ops = {
 260         .ent_blocknr    = fat_ent_blocknr,
 261         .ent_set_ptr    = fat16_ent_set_ptr,
 262         .ent_bread      = fat_ent_bread,
 263         .ent_get        = fat16_ent_get,
 264         .ent_put        = fat16_ent_put,
 265         .ent_next       = fat16_ent_next,
 266 };
 267
 268 static struct fatent_operations fat32_ops = {
 269         .ent_blocknr    = fat_ent_blocknr,
 270         .ent_set_ptr    = fat32_ent_set_ptr,
 271         .ent_bread      = fat_ent_bread,
 272         .ent_get        = fat32_ent_get,
 273         .ent_put        = fat32_ent_put,
 274         .ent_next       = fat32_ent_next,
 275 };
 276
 277 static inline void lock_fat(struct msdos_sb_info *sbi)
 278 {
 279         mutex_lock(&sbi->fat_lock);
 280 }
 281
 282 static inline void unlock_fat(struct msdos_sb_info *sbi)
 283 {
 284         mutex_unlock(&sbi->fat_lock);
 285 }
 286
 287 void fat_ent_access_init(struct super_block *sb)
 288 {
 289         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 290
 291         mutex_init(&sbi->fat_lock);
 292
 293         switch (sbi->fat_bits) {
 294         case 32:
 295                 sbi->fatent_shift = 2;
 296                 sbi->fatent_ops = &fat32_ops;
 297                 break;
 298         case 16:
 299                 sbi->fatent_shift = 1;
 300                 sbi->fatent_ops = &fat16_ops;
 301                 break;
 302         case 12:
 303                 sbi->fatent_shift = -1;
 304                 sbi->fatent_ops = &fat12_ops;
 305                 break;
 306         }
 307 }
 308
 309 static inline int fat_ent_update_ptr(struct super_block *sb,
 310                                      struct fat_entry *fatent,
 311                                      int offset, sector_t blocknr)
 312 {
 313         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 314         struct fatent_operations *ops = sbi->fatent_ops;
 315         struct buffer_head **bhs = fatent->bhs;
 316
 317         /* Is this fatent's blocks including this entry? */
 318         if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
 319                 return 0;
 320         if (sbi->fat_bits == 12) {
 321                 if ((offset + 1) < sb->s_blocksize) {
 322                         /* This entry is on bhs[0]. */
 323                         if (fatent->nr_bhs == 2) {
 324                                 brelse(bhs[1]);
 325                                 fatent->nr_bhs = 1;
 326                         }
 327                 } else {
 328                         /* This entry needs the next block. */
 329                         if (fatent->nr_bhs != 2)
 330                                 return 0;
 331                         if (bhs[1]->b_blocknr != (blocknr + 1))
 332                                 return 0;
 333                 }
 334         }
 335         ops->ent_set_ptr(fatent, offset);
 336         return 1;
 337 }
 338
 339 int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
 340 {
 341         struct super_block *sb = inode->i_sb;
 342         struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
 343         struct fatent_operations *ops = sbi->fatent_ops;
 344         int err, offset;
 345         sector_t blocknr;
 346
 347         if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
 348                 fatent_brelse(fatent);
 349                 fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", entry);
 350                 return -EIO;
 351         }
 352
 353         fatent_set_entry(fatent, entry);
 354         ops->ent_blocknr(sb, entry, &offset, &blocknr);
 355
 356         if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
 357                 fatent_brelse(fatent);
 358                 err = ops->ent_bread(sb, fatent, offset, blocknr);
 359                 if (err)
 360                         return err;
 361         }
 362         return ops->ent_get(fatent);
 363 }
 364
 365 /* FIXME: We can write the blocks as more big chunk. */
 366 static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
 367                           int nr_bhs)
 368 {
 369         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 370         struct buffer_head *c_bh;
 371         int err, n, copy;
 372
 373         err = 0;
 374         for (copy = 1; copy < sbi->fats; copy++) {
 375                 sector_t backup_fat = sbi->fat_length * copy;
 376
 377                 for (n = 0; n < nr_bhs; n++) {
 378                         c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
 379                         if (!c_bh) {
 380                                 err = -ENOMEM;
 381                                 goto error;
 382                         }
 383                         memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
 384                         set_buffer_uptodate(c_bh);
 385                         mark_buffer_dirty(c_bh);
 386                         if (sb->s_flags & MS_SYNCHRONOUS)
 387                                 err = sync_dirty_buffer(c_bh);
 388                         brelse(c_bh);
 389                         if (err)
 390                                 goto error;
 391                 }
 392         }
 393 error:
 394         return err;
 395 }
 396
 397 int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
 398                   int new, int wait)
 399 {
 400         struct super_block *sb = inode->i_sb;
 401         struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 402         int err;
 403
 404         ops->ent_put(fatent, new);
 405         if (wait) {
 406                 err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
 407                 if (err)
 408                         return err;
 409         }
 410         return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
 411 }
 412
 413 static inline int fat_ent_next(struct msdos_sb_info *sbi,
 414                                struct fat_entry *fatent)
 415 {
 416         if (sbi->fatent_ops->ent_next(fatent)) {
 417                 if (fatent->entry < sbi->max_cluster)
 418                         return 1;
 419         }
 420         return 0;
 421 }
 422
 423 static inline int fat_ent_read_block(struct super_block *sb,
 424                                      struct fat_entry *fatent)
 425 {
 426         struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 427         sector_t blocknr;
 428         int offset;
 429
 430         fatent_brelse(fatent);
 431         ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 432         return ops->ent_bread(sb, fatent, offset, blocknr);
 433 }
 434
 435 static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
 436                             struct fat_entry *fatent)
 437 {
 438         int n, i;
 439
 440         for (n = 0; n < fatent->nr_bhs; n++) {
 441                 for (i = 0; i < *nr_bhs; i++) {
 442                         if (fatent->bhs[n] == bhs[i])
 443                                 break;
 444                 }
 445                 if (i == *nr_bhs) {
 446                         get_bh(fatent->bhs[n]);
 447                         bhs[i] = fatent->bhs[n];
 448                         (*nr_bhs)++;
 449                 }
 450         }
 451 }
 452
 453 int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
 454 {
 455         struct super_block *sb = inode->i_sb;
 456         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 457         struct fatent_operations *ops = sbi->fatent_ops;
 458         struct fat_entry fatent, prev_ent;
 459         struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 460         int i, count, err, nr_bhs, idx_clus;
 461
 462         BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));    /* fixed limit */
 463
 464         lock_fat(sbi);
 465         if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
 466             sbi->free_clusters < nr_cluster) {
 467                 unlock_fat(sbi);
 468                 return -ENOSPC;
 469         }
 470
 471         err = nr_bhs = idx_clus = 0;
 472         count = FAT_START_ENT;
 473         fatent_init(&prev_ent);
 474         fatent_init(&fatent);
 475         fatent_set_entry(&fatent, sbi->prev_free + 1);
 476         while (count < sbi->max_cluster) {
 477                 if (fatent.entry >= sbi->max_cluster)
 478                         fatent.entry = FAT_START_ENT;
 479                 fatent_set_entry(&fatent, fatent.entry);
 480                 err = fat_ent_read_block(sb, &fatent);
 481                 if (err)
 482                         goto out;
 483
 484                 /* Find the free entries in a block */
 485                 do {
 486                         if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
 487                                 int entry = fatent.entry;
 488
 489                                 /* make the cluster chain */
 490                                 ops->ent_put(&fatent, FAT_ENT_EOF);
 491                                 if (prev_ent.nr_bhs)
 492                                         ops->ent_put(&prev_ent, entry);
 493
 494                                 fat_collect_bhs(bhs, &nr_bhs, &fatent);
 495
 496                                 sbi->prev_free = entry;
 497                                 if (sbi->free_clusters != -1)
 498                                         sbi->free_clusters--;
 499                                 sb->s_dirt = 1;
 500
 501                                 cluster[idx_clus] = entry;
 502                                 idx_clus++;
 503                                 if (idx_clus == nr_cluster)
 504                                         goto out;
 505
 506                                 /*
 507                                  * fat_collect_bhs() gets ref-count of bhs,
 508                                  * so we can still use the prev_ent.
 509                                  */
 510                                 prev_ent = fatent;
 511                         }
 512                         count++;
 513                         if (count == sbi->max_cluster)
 514                                 break;
 515                 } while (fat_ent_next(sbi, &fatent));
 516         }
 517
 518         /* Couldn't allocate the free entries */
 519         sbi->free_clusters = 0;
 520         sbi->free_clus_valid = 1;
 521         sb->s_dirt = 1;
 522         err = -ENOSPC;
 523
 524 out:
 525         unlock_fat(sbi);
 526         fatent_brelse(&fatent);
 527         if (!err) {
 528                 if (inode_needs_sync(inode))
 529                         err = fat_sync_bhs(bhs, nr_bhs);
 530                 if (!err)
 531                         err = fat_mirror_bhs(sb, bhs, nr_bhs);
 532         }
 533         for (i = 0; i < nr_bhs; i++)
 534                 brelse(bhs[i]);
 535
 536         if (err && idx_clus)
 537                 fat_free_clusters(inode, cluster[0]);
 538
 539         return err;
 540 }
 541
 542 int fat_free_clusters(struct inode *inode, int cluster)
 543 {
 544         struct super_block *sb = inode->i_sb;
 545         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 546         struct fatent_operations *ops = sbi->fatent_ops;
 547         struct fat_entry fatent;
 548         struct buffer_head *bhs[MAX_BUF_PER_PAGE];
 549         int i, err, nr_bhs;
 550         int first_cl = cluster;
 551
 552         nr_bhs = 0;
 553         fatent_init(&fatent);
 554         lock_fat(sbi);
 555         do {
 556                 cluster = fat_ent_read(inode, &fatent, cluster);
 557                 if (cluster < 0) {
 558                         err = cluster;
 559                         goto error;
 560                 } else if (cluster == FAT_ENT_FREE) {
 561                         fat_fs_panic(sb, "%s: deleting FAT entry beyond EOF",
 562                                      __func__);
 563                         err = -EIO;
 564                         goto error;
 565                 }
 566
 567                 /*
 568                  * Issue discard for the sectors we no longer care about,
 569                  * batching contiguous clusters into one request
 570                  */
 571                 if (cluster != fatent.entry + 1) {
 572                         int nr_clus = fatent.entry - first_cl + 1;
 573
 574                         sb_issue_discard(sb, fat_clus_to_blknr(sbi, first_cl),
 575                                          nr_clus * sbi->sec_per_clus);
 576                         first_cl = cluster;
 577                 }
 578
 579                 ops->ent_put(&fatent, FAT_ENT_FREE);
 580                 if (sbi->free_clusters != -1) {
 581                         sbi->free_clusters++;
 582                         sb->s_dirt = 1;
 583                 }
 584
 585                 if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
 586                         if (sb->s_flags & MS_SYNCHRONOUS) {
 587                                 err = fat_sync_bhs(bhs, nr_bhs);
 588                                 if (err)
 589                                         goto error;
 590                         }
 591                         err = fat_mirror_bhs(sb, bhs, nr_bhs);
 592                         if (err)
 593                                 goto error;
 594                         for (i = 0; i < nr_bhs; i++)
 595                                 brelse(bhs[i]);
 596                         nr_bhs = 0;
 597                 }
 598                 fat_collect_bhs(bhs, &nr_bhs, &fatent);
 599         } while (cluster != FAT_ENT_EOF);
 600
 601         if (sb->s_flags & MS_SYNCHRONOUS) {
 602                 err = fat_sync_bhs(bhs, nr_bhs);
 603                 if (err)
 604                         goto error;
 605         }
 606         err = fat_mirror_bhs(sb, bhs, nr_bhs);
 607 error:
 608         fatent_brelse(&fatent);
 609         for (i = 0; i < nr_bhs; i++)
 610                 brelse(bhs[i]);
 611         unlock_fat(sbi);
 612
 613         return err;
 614 }
 615
 616 EXPORT_SYMBOL_GPL(fat_free_clusters);
 617
 618 /* 128kb is the whole sectors for FAT12 and FAT16 */
 619 #define FAT_READA_SIZE          (128 * 1024)
 620
 621 static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
 622                           unsigned long reada_blocks)
 623 {
 624         struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
 625         sector_t blocknr;
 626         int i, offset;
 627
 628         ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
 629
 630         for (i = 0; i < reada_blocks; i++)
 631                 sb_breadahead(sb, blocknr + i);
 632 }
 633
 634 int fat_count_free_clusters(struct super_block *sb)
 635 {
 636         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 637         struct fatent_operations *ops = sbi->fatent_ops;
 638         struct fat_entry fatent;
 639         unsigned long reada_blocks, reada_mask, cur_block;
 640         int err = 0, free;
 641
 642         lock_fat(sbi);
 643         if (sbi->free_clusters != -1 && sbi->free_clus_valid)
 644                 goto out;
 645
 646         reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
 647         reada_mask = reada_blocks - 1;
 648         cur_block = 0;
 649
 650         free = 0;
 651         fatent_init(&fatent);
 652         fatent_set_entry(&fatent, FAT_START_ENT);
 653         while (fatent.entry < sbi->max_cluster) {
 654                 /* readahead of fat blocks */
 655                 if ((cur_block & reada_mask) == 0) {
 656                         unsigned long rest = sbi->fat_length - cur_block;
 657                         fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
 658                 }
 659                 cur_block++;
 660
 661                 err = fat_ent_read_block(sb, &fatent);
 662                 if (err)
 663                         goto out;
 664
 665                 do {
 666                         if (ops->ent_get(&fatent) == FAT_ENT_FREE)
 667                                 free++;
 668                 } while (fat_ent_next(sbi, &fatent));
 669         }
 670         sbi->free_clusters = free;
 671         sbi->free_clus_valid = 1;
 672         sb->s_dirt = 1;
 673         fatent_brelse(&fatent);
 674 out:
 675         unlock_fat(sbi);
 676         return err;
 677 }