119 lines
3.0 KiB
C
119 lines
3.0 KiB
C
#ident "$Id: open.c,v 1.2 2004/12/15 20:29:17 hpa Exp $"
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/* ----------------------------------------------------------------------- *
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*
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* Copyright 2004 H. Peter Anvin - All Rights Reserved
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, Inc., 53 Temple Place Ste 330,
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* Boston MA 02111-1307, USA; either version 2 of the License, or
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* (at your option) any later version; incorporated herein by reference.
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*
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* ----------------------------------------------------------------------- */
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/*
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* open.c
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*
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* Open a FAT filesystem and compute some initial values; return NULL
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* on failure.
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*/
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#include <stdlib.h>
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#include "libfatint.h"
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#include "ulint.h"
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struct libfat_filesystem *
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libfat_open(int (*readfunc)(intptr_t, void *, size_t, libfat_sector_t),
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intptr_t readptr)
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{
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struct libfat_filesystem *fs = NULL;
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struct fat_bootsect *bs;
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int i;
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uint32_t sectors, fatsize, minfatsize, rootdirsize;
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uint32_t nclusters;
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fs = malloc(sizeof(struct libfat_filesystem));
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if ( !fs )
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goto barf;
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fs->sectors = NULL;
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fs->read = readfunc;
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fs->readptr = readptr;
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bs = libfat_get_sector(fs, 0);
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if ( !bs )
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goto barf;
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if ( read16(&bs->bsBytesPerSec) != LIBFAT_SECTOR_SIZE )
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goto barf;
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for ( i = 0 ; i <= 8 ; i++ ) {
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if ( (uint8_t)(1 << i) == read8(&bs->bsSecPerClust) )
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break;
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}
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if ( i > 8 )
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goto barf;
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fs->clustsize = 1 << i; /* Treat 0 as 2^8 = 64K */
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fs->clustshift = i;
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sectors = read16(&bs->bsSectors);
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if ( !sectors )
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sectors = read32(&bs->bsHugeSectors);
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fs->end = sectors;
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fs->fat = read16(&bs->bsResSectors);
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fatsize = read16(&bs->bsFATsecs);
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if ( !fatsize )
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fatsize = read32(&bs->u.fat32.bpb_fatsz32);
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fs->rootdir = fs->fat + fatsize * read8(&bs->bsFATs);
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rootdirsize = ((read16(&bs->bsRootDirEnts) << 5) + LIBFAT_SECTOR_MASK)
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>> LIBFAT_SECTOR_SHIFT;
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fs->data = fs->rootdir + rootdirsize;
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/* Sanity checking */
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if ( fs->data >= fs->end )
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goto barf;
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/* Figure out how many clusters */
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nclusters = (fs->end - fs->data) >> fs->clustshift;
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fs->endcluster = nclusters + 2;
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if ( nclusters <= 0xff4 ) {
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fs->fat_type = FAT12;
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minfatsize = fs->endcluster + (fs->endcluster >> 1);
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} else if ( nclusters <= 0xfff4 ) {
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fs->fat_type = FAT16;
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minfatsize = fs->endcluster << 1;
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} else if ( nclusters <= 0xffffff4 ) {
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fs->fat_type = FAT28;
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minfatsize = fs->endcluster << 2;
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} else
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goto barf; /* Impossibly many clusters */
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minfatsize = (minfatsize + LIBFAT_SECTOR_SIZE-1) >> LIBFAT_SECTOR_SHIFT;
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if ( minfatsize > fatsize )
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goto barf; /* The FATs don't fit */
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if ( fs->fat_type == FAT28 )
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fs->rootcluster = read32(&bs->u.fat32.bpb_rootclus);
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else
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fs->rootcluster = 0;
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return fs; /* All good */
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barf:
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if ( fs )
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free(fs);
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return NULL;
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}
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void libfat_close(struct libfat_filesystem *fs)
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{
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libfat_flush(fs);
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free(fs);
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}
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