| /* |
| * linux/fs/msdos/fat.c |
| * |
| * Written 1992,1993 by Werner Almesberger |
| */ |
| |
| #include <linux/msdos_fs.h> |
| #include <linux/kernel.h> |
| #include <linux/errno.h> |
| #include <linux/stat.h> |
| |
| |
| static struct fat_cache *fat_cache,cache[FAT_CACHE]; |
| |
| /* Returns the this'th FAT entry, -1 if it is an end-of-file entry. If |
| new_value is != -1, that FAT entry is replaced by it. */ |
| |
| int fat_access(struct super_block *sb,int nr,int new_value) |
| { |
| struct buffer_head *bh,*bh2,*c_bh,*c_bh2; |
| unsigned char *p_first,*p_last; |
| void *data,*data2,*c_data,*c_data2; |
| int first,last,next,copy; |
| |
| if ((unsigned) (nr-2) >= MSDOS_SB(sb)->clusters) return 0; |
| if (MSDOS_SB(sb)->fat_bits == 16) first = last = nr*2; |
| else { |
| first = nr*3/2; |
| last = first+1; |
| } |
| if (!(bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(first >> |
| SECTOR_BITS),&data))) { |
| printk("bread in fat_access failed\n"); |
| return 0; |
| } |
| if ((first >> SECTOR_BITS) == (last >> SECTOR_BITS)) { |
| bh2 = bh; |
| data2 = data; |
| } |
| else { |
| if (!(bh2 = msdos_sread(sb->s_dev,MSDOS_SB(sb)->fat_start+(last |
| >> SECTOR_BITS),&data2))) { |
| brelse(bh); |
| printk("bread in fat_access failed\n"); |
| return 0; |
| } |
| } |
| if (MSDOS_SB(sb)->fat_bits == 16) { |
| p_first = p_last = NULL; /* GCC needs that stuff */ |
| next = CF_LE_W(((unsigned short *) data)[(first & |
| (SECTOR_SIZE-1)) >> 1]); |
| if (next >= 0xfff7) next = -1; |
| } |
| else { |
| p_first = &((unsigned char *) data)[first & (SECTOR_SIZE-1)]; |
| p_last = &((unsigned char *) data2)[(first+1) & |
| (SECTOR_SIZE-1)]; |
| if (nr & 1) next = ((*p_first >> 4) | (*p_last << 4)) & 0xfff; |
| else next = (*p_first+(*p_last << 8)) & 0xfff; |
| if (next >= 0xff7) next = -1; |
| } |
| if (new_value != -1) { |
| if (MSDOS_SB(sb)->fat_bits == 16) |
| ((unsigned short *) data)[(first & (SECTOR_SIZE-1)) >> |
| 1] = CT_LE_W(new_value); |
| else { |
| if (nr & 1) { |
| *p_first = (*p_first & 0xf) | (new_value << 4); |
| *p_last = new_value >> 4; |
| } |
| else { |
| *p_first = new_value & 0xff; |
| *p_last = (*p_last & 0xf0) | (new_value >> 8); |
| } |
| bh2->b_dirt = 1; |
| } |
| bh->b_dirt = 1; |
| for (copy = 1; copy < MSDOS_SB(sb)->fats; copy++) { |
| if (!(c_bh = msdos_sread(sb->s_dev,MSDOS_SB(sb)-> |
| fat_start+(first >> SECTOR_BITS)+MSDOS_SB(sb)-> |
| fat_length*copy,&c_data))) break; |
| memcpy(c_data,data,SECTOR_SIZE); |
| c_bh->b_dirt = 1; |
| if (data != data2 || bh != bh2) { |
| if (!(c_bh2 = msdos_sread(sb->s_dev, |
| MSDOS_SB(sb)->fat_start+(first >> |
| SECTOR_BITS)+MSDOS_SB(sb)->fat_length*copy |
| +1,&c_data2))) { |
| brelse(c_bh); |
| break; |
| } |
| memcpy(c_data2,data2,SECTOR_SIZE); |
| brelse(c_bh2); |
| } |
| brelse(c_bh); |
| } |
| } |
| brelse(bh); |
| if (data != data2) brelse(bh2); |
| return next; |
| } |
| |
| |
| void cache_init(void) |
| { |
| static int initialized = 0; |
| int count; |
| |
| if (initialized) return; |
| fat_cache = &cache[0]; |
| for (count = 0; count < FAT_CACHE; count++) { |
| cache[count].device = 0; |
| cache[count].next = count == FAT_CACHE-1 ? NULL : |
| &cache[count+1]; |
| } |
| initialized = 1; |
| } |
| |
| |
| void cache_lookup(struct inode *inode,int cluster,int *f_clu,int *d_clu) |
| { |
| struct fat_cache *walk; |
| |
| #ifdef DEBUG |
| printk("cache lookup: <%d,%d> %d (%d,%d) -> ",inode->i_dev,inode->i_ino,cluster, |
| *f_clu,*d_clu); |
| #endif |
| for (walk = fat_cache; walk; walk = walk->next) |
| if (inode->i_dev == walk->device && walk->ino == inode->i_ino && |
| walk->file_cluster <= cluster && walk->file_cluster > |
| *f_clu) { |
| *d_clu = walk->disk_cluster; |
| #ifdef DEBUG |
| printk("cache hit: %d (%d)\n",walk->file_cluster,*d_clu); |
| #endif |
| if ((*f_clu = walk->file_cluster) == cluster) return; |
| } |
| #ifdef DEBUG |
| printk("cache miss\n"); |
| #endif |
| } |
| |
| |
| #ifdef DEBUG |
| static void list_cache(void) |
| { |
| struct fat_cache *walk; |
| |
| for (walk = fat_cache; walk; walk = walk->next) { |
| if (walk->device) |
| printk("<%d,%d>(%d,%d) ",walk->device,walk->ino, |
| walk->file_cluster,walk->disk_cluster); |
| else printk("-- "); |
| } |
| printk("\n"); |
| } |
| #endif |
| |
| |
| void cache_add(struct inode *inode,int f_clu,int d_clu) |
| { |
| struct fat_cache *walk,*last; |
| |
| #ifdef DEBUG |
| printk("cache add: <%d,%d> %d (%d)\n",inode->i_dev,inode->i_ino,f_clu,d_clu); |
| #endif |
| last = NULL; |
| for (walk = fat_cache; walk->next; walk = (last = walk)->next) |
| if (inode->i_dev == walk->device && walk->ino == inode->i_ino && |
| walk->file_cluster == f_clu) { |
| if (walk->disk_cluster != d_clu) { |
| printk("FAT cache corruption"); |
| cache_inval_inode(inode); |
| return; |
| } |
| /* update LRU */ |
| if (last == NULL) return; |
| last->next = walk->next; |
| walk->next = fat_cache; |
| fat_cache = walk; |
| #ifdef DEBUG |
| list_cache(); |
| #endif |
| return; |
| } |
| walk->device = inode->i_dev; |
| walk->ino = inode->i_ino; |
| walk->file_cluster = f_clu; |
| walk->disk_cluster = d_clu; |
| last->next = NULL; |
| walk->next = fat_cache; |
| fat_cache = walk; |
| #ifdef DEBUG |
| list_cache(); |
| #endif |
| } |
| |
| |
| /* Cache invalidation occurs rarely, thus the LRU chain is not updated. It |
| fixes itself after a while. */ |
| |
| void cache_inval_inode(struct inode *inode) |
| { |
| struct fat_cache *walk; |
| |
| for (walk = fat_cache; walk; walk = walk->next) |
| if (walk->device == inode->i_dev && walk->ino == inode->i_ino) |
| walk->device = 0; |
| } |
| |
| |
| void cache_inval_dev(int device) |
| { |
| struct fat_cache *walk; |
| |
| for (walk = fat_cache; walk; walk = walk->next) |
| if (walk->device == device) walk->device = 0; |
| } |
| |
| |
| int get_cluster(struct inode *inode,int cluster) |
| { |
| int nr,count; |
| |
| if (!(nr = MSDOS_I(inode)->i_start)) return 0; |
| if (!cluster) return nr; |
| count = 0; |
| for (cache_lookup(inode,cluster,&count,&nr); count < cluster; |
| count++) { |
| if ((nr = fat_access(inode->i_sb,nr,-1)) == -1) return 0; |
| if (!nr) return 0; |
| } |
| cache_add(inode,cluster,nr); |
| return nr; |
| } |
| |
| |
| int msdos_smap(struct inode *inode,int sector) |
| { |
| struct msdos_sb_info *sb; |
| int cluster,offset; |
| |
| sb = MSDOS_SB(inode->i_sb); |
| if (inode->i_ino == MSDOS_ROOT_INO || (S_ISDIR(inode->i_mode) && |
| !MSDOS_I(inode)->i_start)) { |
| if (sector >= sb->dir_entries >> MSDOS_DPS_BITS) return 0; |
| return sector+sb->dir_start; |
| } |
| cluster = sector/sb->cluster_size; |
| offset = sector % sb->cluster_size; |
| if (!(cluster = get_cluster(inode,cluster))) return 0; |
| return (cluster-2)*sb->cluster_size+sb->data_start+offset; |
| } |
| |
| |
| /* Free all clusters after the skip'th cluster. Doesn't use the cache, |
| because this way we get an additional sanity check. */ |
| |
| int fat_free(struct inode *inode,int skip) |
| { |
| int nr,last; |
| |
| if (!(nr = MSDOS_I(inode)->i_start)) return 0; |
| last = 0; |
| while (skip--) { |
| last = nr; |
| if ((nr = fat_access(inode->i_sb,nr,-1)) == -1) return 0; |
| if (!nr) { |
| printk("fat_free: skipped EOF\n"); |
| return -EIO; |
| } |
| } |
| if (last) |
| fat_access(inode->i_sb,last,MSDOS_SB(inode->i_sb)->fat_bits == |
| 12 ? 0xff8 : 0xfff8); |
| else { |
| MSDOS_I(inode)->i_start = 0; |
| inode->i_dirt = 1; |
| } |
| lock_fat(inode->i_sb); |
| while (nr != -1) { |
| if (!(nr = fat_access(inode->i_sb,nr,0))) { |
| fs_panic(inode->i_sb,"fat_free: deleting beyond EOF"); |
| break; |
| } |
| if (MSDOS_SB(inode->i_sb)->free_clusters != -1) |
| MSDOS_SB(inode->i_sb)->free_clusters++; |
| inode->i_blocks -= MSDOS_SB(inode->i_sb)->cluster_size; |
| } |
| unlock_fat(inode->i_sb); |
| cache_inval_inode(inode); |
| return 0; |
| } |