fs/msdos/fat.c

/* */
This source file includes following definitions.
fat_access
cache_init
cache_lookup
list_cache
cache_add
cache_inval_inode
cache_inval_dev
get_cluster
msdos_smap
fat_free
   1 /*
   2  *  linux/fs/msdos/fat.c
   3  *
   4  *  Written 1992 by Werner Almesberger
   5  */
   6 
   7 #include <linux/msdos_fs.h>
   8 #include <linux/kernel.h>
   9 #include <linux/errno.h>
  10 #include <linux/stat.h>
  11 
  12 static struct fat_cache *fat_cache,cache[FAT_CACHE];
  13 
  14 /* Returns the this'th FAT entry, -1 if it is an end-of-file entry. If
  15    new_value is != -1, that FAT entry is replaced by it. */
  16 
  17 int fat_access(struct super_block *sb,int this,int new_value)
     /*  */
  18 {
  19         struct buffer_head *bh,*bh2,*c_bh,*c_bh2;
  20         unsigned char *p_first,*p_last;
  21         void *data,*data2,*c_data,*c_data2;
  22         int first,last,next,copy;
  23 
  24         if (MSDOS_SB(sb)->fat_bits == 16) first = last = this*2;
  25         else {
  26                 first = this*3/2;
  27                 last = first+1;
  28         }
  29         if (!(bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(first >>
  30             SECTOR_BITS),&data))) {
  31                 printk("bread in fat_access failed\r\n");
  32                 return 0;
  33         }
  34         if ((first >> SECTOR_BITS) == (last >> SECTOR_BITS)) {
  35                 bh2 = bh;
  36                 data2 = data;
  37         }
  38         else {
  39                 if (!(bh2 = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(last
  40                     >> SECTOR_BITS),&data2))) {
  41                         brelse(bh);
  42                         printk("bread in fat_access failed\r\n");
  43                         return 0;
  44                 }
  45         }
  46         if (MSDOS_SB(sb)->fat_bits == 16) {
  47                 next = ((unsigned short *) data)[(first & (SECTOR_SIZE-1))
  48                     >> 1];
  49                 if (next >= 0xfff8) next = -1;
  50         }
  51         else {
  52                 p_first = &((unsigned char *) data)[first & (SECTOR_SIZE-1)];
  53                 p_last = &((unsigned char *) data2)[(first+1) &
  54                     (SECTOR_SIZE-1)];
  55                 if (this & 1) next = ((*p_first >> 4) | (*p_last << 4)) & 0xfff;
  56                 else next = (*p_first+(*p_last << 8)) & 0xfff;
  57                 if (next >= 0xff8) next = -1;
  58         }
  59         if (new_value != -1) {
  60                 if (MSDOS_SB(sb)->fat_bits == 16)
  61                         ((unsigned short *) data)[(first & (SECTOR_SIZE-1)) >>
  62                             1] = new_value;
  63                 else {
  64                         if (this & 1) {
  65                                 *p_first = (*p_first & 0xf) | (new_value << 4);
  66                                 *p_last = new_value >> 4;
  67                         }
  68                         else {
  69                                 *p_first = new_value & 0xff;
  70                                 *p_last = (*p_last & 0xf0) | (new_value >> 8);
  71                         }
  72                         bh2->b_dirt = 1;
  73                 }
  74                 bh->b_dirt = 1;
  75                 for (copy = 1; copy < MSDOS_SB(sb)->fats; copy++) {
  76                         if (!(c_bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)->
  77                             fat_start+(first >> SECTOR_BITS)+MSDOS_SB(sb)->
  78                             fat_length*copy,&c_data))) break;
  79                         memcpy(c_data,data,SECTOR_SIZE);
  80                         c_bh->b_dirt = 1;
  81                         if (data != data2 || bh != bh2) {
  82                                 if (!(c_bh2 = msdos_sread(sb->s_dev,
  83                                     MSDOS_SB(sb)->fat_start+(first >>
  84                                     SECTOR_BITS)+MSDOS_SB(sb)->fat_length*copy
  85                                     +1,&c_data2))) {
  86                                         brelse(c_bh);
  87                                         break;
  88                                 }
  89                                 memcpy(c_data2,data2,SECTOR_SIZE);
  90                                 brelse(c_bh2);
  91                         }
  92                         brelse(c_bh);
  93                 }
  94         }
  95         brelse(bh);
  96         if (data != data2) brelse(bh2);
  97         return next;
  98 }
  99 
 100 
 101 void cache_init(void)
     /*  */
 102 {
 103         static int initialized = 0;
 104         int count;
 105 
 106         if (initialized) return;
 107         fat_cache = &cache[0];
 108         for (count = 0; count < FAT_CACHE; count++) {
 109                 cache[count].device = 0;
 110                 cache[count].next = count == FAT_CACHE-1 ? NULL :
 111                     &cache[count+1];
 112         }
 113         initialized = 1;
 114 }
 115 
 116 
 117 void cache_lookup(struct inode *inode,int cluster,int *f_clu,int *d_clu)
     /*  */
 118 {
 119         struct fat_cache *walk;
 120 
 121 #ifdef DEBUG
 122 printk("cache lookup: %d\r\n",*f_clu);
 123 #endif
 124         for (walk = fat_cache; walk; walk = walk->next)
 125                 if (inode->i_dev == walk->device && walk->ino == inode->i_ino &&
 126                     walk->file_cluster <= cluster && walk->file_cluster >
 127                     *f_clu) {
 128                         *d_clu = walk->disk_cluster;
 129 #ifdef DEBUG
 130 printk("cache hit: %d (%d)\r\n",walk->file_cluster,*d_clu);
 131 #endif
 132                         if ((*f_clu = walk->file_cluster) == cluster) return;
 133                 }
 134 }
 135 
 136 
 137 #ifdef DEBUG
 138 static void list_cache(void)
     /*  */
 139 {
 140         struct fat_cache *walk;
 141 
 142         for (walk = fat_cache; walk; walk = walk->next) {
 143                 if (walk->device) printk("(%d,%d) ",walk->file_cluster,
 144                         walk->disk_cluster);
 145                 else printk("-- ");
 146         }
 147         printk("\r\n");
 148 }
 149 #endif
 150 
 151 
 152 void cache_add(struct inode *inode,int f_clu,int d_clu)
     /*  */
 153 {
 154         struct fat_cache *walk,*last;
 155 
 156 #ifdef DEBUG
 157 printk("cache add: %d (%d)\r\n",f_clu,d_clu);
 158 #endif
 159         last = NULL;
 160         for (walk = fat_cache; walk->next; walk = (last = walk)->next)
 161                 if (inode->i_dev == walk->device && walk->ino == inode->i_ino &&
 162                     walk->file_cluster == f_clu) {
 163                         if (walk->disk_cluster != d_clu)
 164                                 panic("FAT cache corruption");
 165                         /* update LRU */
 166                         if (last == NULL) return;
 167                         last->next = walk->next;
 168                         walk->next = fat_cache;
 169                         fat_cache = walk;
 170 #ifdef DEBUG
 171 list_cache();
 172 #endif
 173                         return;
 174                 }
 175         walk->device = inode->i_dev;
 176         walk->ino = inode->i_ino;
 177         walk->file_cluster = f_clu;
 178         walk->disk_cluster = d_clu;
 179         last->next = NULL;
 180         walk->next = fat_cache;
 181         fat_cache = walk;
 182 #ifdef DEBUG
 183 list_cache();
 184 #endif
 185 }
 186 
 187 
 188 /* Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 189    fixes itself after a while. */
 190 
 191 void cache_inval_inode(struct inode *inode)
     /*  */
 192 {
 193         struct fat_cache *walk;
 194 
 195         for (walk = fat_cache; walk; walk = walk->next)
 196                 if (walk->device == inode->i_dev && walk->ino == inode->i_ino)
 197                         walk->device = 0;
 198 }
 199 
 200 
 201 void cache_inval_dev(int device)
     /*  */
 202 {
 203         struct fat_cache *walk;
 204 
 205         for (walk = fat_cache; walk; walk = walk->next)
 206                 if (walk->device == device) walk->device = 0;
 207 }
 208 
 209 
 210 int get_cluster(struct inode *inode,int cluster)
     /*  */
 211 {
 212         int this,count;
 213 
 214         if (!(this = inode->i_data[D_START])) return 0;
 215         if (!cluster) return this;
 216         count = 0;
 217         for (cache_lookup(inode,cluster,&count,&this); count < cluster;
 218             count++) {
 219                 if ((this = fat_access(inode->i_sb,this,-1)) == -1) return 0;
 220                 if (!this) return 0;
 221         }
 222         cache_add(inode,cluster,this);
 223         return this;
 224 }
 225 
 226 
 227 int msdos_smap(struct inode *inode,int sector)
     /*  */
 228 {
 229         struct msdos_sb_info *sb;
 230         int cluster,offset;
 231 
 232         sb = MSDOS_SB(inode->i_sb);
 233         if (inode->i_ino == MSDOS_ROOT_INO || (S_ISDIR(inode->i_mode) &&
 234             !inode->i_data[D_START])) {
 235                 if (sector >= sb->dir_entries >> MSDOS_DPS_BITS) return 0;
 236                 return sector+sb->dir_start;
 237         }
 238         cluster = sector/sb->cluster_size;
 239         offset = sector % sb->cluster_size;
 240         if (!(cluster = get_cluster(inode,cluster))) return 0;
 241         return (cluster-2)*sb->cluster_size+sb->data_start+offset;
 242 }
 243 
 244 
 245 /* Free all clusters after the skip'th cluster. Doesn't use the cache,
 246    because this way we get an additional sanity check. */
 247 
 248 int fat_free(struct inode *inode,int skip)
     /*  */
 249 {
 250         int this,last;
 251 
 252         if (!(this = inode->i_data[D_START])) return 0;
 253         last = 0;
 254         while (skip--) {
 255                 last = this;
 256                 if ((this = fat_access(inode->i_sb,this,-1)) == -1)
 257                         return 0;
 258                 if (!this) {
 259                         printk("fat_free: skipped EOF\r\n");
 260                         return -EIO;
 261                 }
 262         }
 263         if (last)
 264                 fat_access(inode->i_sb,last,MSDOS_SB(inode->i_sb)->fat_bits ==
 265                     12 ? 0xff8 : 0xfff8);
 266         else {
 267                 inode->i_data[D_START] = 0;
 268                 inode->i_dirt = 1;
 269         }
 270         while (this != -1)
 271                 if (!(this = fat_access(inode->i_sb,this,0)))
 272                         panic("fat_free: deleting beyond EOF");
 273         cache_inval_inode(inode);
 274         return 0;
 275 }
/* */
root/fs/msdos/fat.c

DEFINITIONS
