block: pass gfp_mask and flags to sb_issue_discard
[linux-2.6.git] / 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         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
95 err_brelse:
96         brelse(bhs[0]);
97 err:
98         printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n", (llu)blocknr);
99         return -EIO;
100 }
101
102 static 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                 printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
112                        (llu)blocknr);
113                 return -EIO;
114         }
115         fatent->nr_bhs = 1;
116         ops->ent_set_ptr(fatent, offset);
117         return 0;
118 }
119
120 static 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
138 static 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
147 static 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
156 static 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
178 static 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
187 static 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
198 static 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
228 static 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
240 static 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
252 static 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
261 static 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
270 static 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
279 static inline void lock_fat(struct msdos_sb_info *sbi)
280 {
281         mutex_lock(&sbi->fat_lock);
282 }
283
284 static inline void unlock_fat(struct msdos_sb_info *sbi)
285 {
286         mutex_unlock(&sbi->fat_lock);
287 }
288
289 void 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
311 static 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
341 int 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. */
368 static 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         }
395 error:
396         return err;
397 }
398
399 int 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
415 static 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
425 static 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
437 static 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
455 int 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
526 out:
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
544 int 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,
582                                         BLKDEV_IFL_WAIT | BLKDEV_IFL_BARRIER);
583
584                                 first_cl = cluster;
585                         }
586                 }
587
588                 ops->ent_put(&fatent, FAT_ENT_FREE);
589                 if (sbi->free_clusters != -1) {
590                         sbi->free_clusters++;
591                         sb->s_dirt = 1;
592                 }
593
594                 if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
595                         if (sb->s_flags & MS_SYNCHRONOUS) {
596                                 err = fat_sync_bhs(bhs, nr_bhs);
597                                 if (err)
598                                         goto error;
599                         }
600                         err = fat_mirror_bhs(sb, bhs, nr_bhs);
601                         if (err)
602                                 goto error;
603                         for (i = 0; i < nr_bhs; i++)
604                                 brelse(bhs[i]);
605                         nr_bhs = 0;
606                 }
607                 fat_collect_bhs(bhs, &nr_bhs, &fatent);
608         } while (cluster != FAT_ENT_EOF);
609
610         if (sb->s_flags & MS_SYNCHRONOUS) {
611                 err = fat_sync_bhs(bhs, nr_bhs);
612                 if (err)
613                         goto error;
614         }
615         err = fat_mirror_bhs(sb, bhs, nr_bhs);
616 error:
617         fatent_brelse(&fatent);
618         for (i = 0; i < nr_bhs; i++)
619                 brelse(bhs[i]);
620         unlock_fat(sbi);
621
622         return err;
623 }
624
625 EXPORT_SYMBOL_GPL(fat_free_clusters);
626
627 /* 128kb is the whole sectors for FAT12 and FAT16 */
628 #define FAT_READA_SIZE          (128 * 1024)
629
630 static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
631                           unsigned long reada_blocks)
632 {
633         struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
634         sector_t blocknr;
635         int i, offset;
636
637         ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
638
639         for (i = 0; i < reada_blocks; i++)
640                 sb_breadahead(sb, blocknr + i);
641 }
642
643 int fat_count_free_clusters(struct super_block *sb)
644 {
645         struct msdos_sb_info *sbi = MSDOS_SB(sb);
646         struct fatent_operations *ops = sbi->fatent_ops;
647         struct fat_entry fatent;
648         unsigned long reada_blocks, reada_mask, cur_block;
649         int err = 0, free;
650
651         lock_fat(sbi);
652         if (sbi->free_clusters != -1 && sbi->free_clus_valid)
653                 goto out;
654
655         reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
656         reada_mask = reada_blocks - 1;
657         cur_block = 0;
658
659         free = 0;
660         fatent_init(&fatent);
661         fatent_set_entry(&fatent, FAT_START_ENT);
662         while (fatent.entry < sbi->max_cluster) {
663                 /* readahead of fat blocks */
664                 if ((cur_block & reada_mask) == 0) {
665                         unsigned long rest = sbi->fat_length - cur_block;
666                         fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
667                 }
668                 cur_block++;
669
670                 err = fat_ent_read_block(sb, &fatent);
671                 if (err)
672                         goto out;
673
674                 do {
675                         if (ops->ent_get(&fatent) == FAT_ENT_FREE)
676                                 free++;
677                 } while (fat_ent_next(sbi, &fatent));
678         }
679         sbi->free_clusters = free;
680         sbi->free_clus_valid = 1;
681         sb->s_dirt = 1;
682         fatent_brelse(&fatent);
683 out:
684         unlock_fat(sbi);
685         return err;
686 }