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