Home | History | Annotate | Download | only in libfat 
      1 /* ----------------------------------------------------------------------- *
      2  *
      3  *   Copyright 2004-2008 H. Peter Anvin - All Rights Reserved
      4  *
      5  *   This program is free software; you can redistribute it and/or modify
      6  *   it under the terms of the GNU General Public License as published by
      7  *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
      8  *   Boston MA 02111-1307, USA; either version 2 of the License, or
      9  *   (at your option) any later version; incorporated herein by reference.
     10  *
     11  * ----------------------------------------------------------------------- */
     12 
     13 /*
     14  * open.c
     15  *
     16  * Open a FAT filesystem and compute some initial values; return NULL
     17  * on failure.
     18  */
     19 
     20 #include <stdlib.h>
     21 #include "libfatint.h"
     22 #include "ulint.h"
     23 
     24 struct libfat_filesystem *
     25 libfat_open(int (*readfunc) (intptr_t, void *, size_t, libfat_sector_t),
     26 	    intptr_t readptr)
     27 {
     28     struct libfat_filesystem *fs = NULL;
     29     struct fat_bootsect *bs;
     30     int i;
     31     uint32_t sectors, fatsize, minfatsize, rootdirsize;
     32     uint32_t nclusters;
     33 
     34     fs = malloc(sizeof(struct libfat_filesystem));
     35     if (!fs)
     36 	goto barf;
     37 
     38     fs->sectors = NULL;
     39     fs->read = readfunc;
     40     fs->readptr = readptr;
     41 
     42     bs = libfat_get_sector(fs, 0);
     43     if (!bs)
     44 	goto barf;
     45 
     46     if (read16(&bs->bsBytesPerSec) != LIBFAT_SECTOR_SIZE)
     47 	goto barf;
     48 
     49     for (i = 0; i <= 8; i++) {
     50 	if ((uint8_t) (1 << i) == read8(&bs->bsSecPerClust))
     51 	    break;
     52     }
     53     if (i > 8)
     54 	goto barf;
     55     fs->clustsize = 1 << i;	/* Treat 0 as 2^8 = 64K */
     56     fs->clustshift = i;
     57 
     58     sectors = read16(&bs->bsSectors);
     59     if (!sectors)
     60 	sectors = read32(&bs->bsHugeSectors);
     61 
     62     fs->end = sectors;
     63 
     64     fs->fat = read16(&bs->bsResSectors);
     65     fatsize = read16(&bs->bsFATsecs);
     66     if (!fatsize)
     67 	fatsize = read32(&bs->u.fat32.bpb_fatsz32);
     68 
     69     fs->rootdir = fs->fat + fatsize * read8(&bs->bsFATs);
     70 
     71     rootdirsize = ((read16(&bs->bsRootDirEnts) << 5) + LIBFAT_SECTOR_MASK)
     72 	>> LIBFAT_SECTOR_SHIFT;
     73     fs->data = fs->rootdir + rootdirsize;
     74 
     75     /* Sanity checking */
     76     if (fs->data >= fs->end)
     77 	goto barf;
     78 
     79     /* Figure out how many clusters */
     80     nclusters = (fs->end - fs->data) >> fs->clustshift;
     81     fs->endcluster = nclusters + 2;
     82 
     83     if (nclusters <= 0xff4) {
     84 	fs->fat_type = FAT12;
     85 	minfatsize = fs->endcluster + (fs->endcluster >> 1);
     86     } else if (nclusters <= 0xfff4) {
     87 	fs->fat_type = FAT16;
     88 	minfatsize = fs->endcluster << 1;
     89     } else if (nclusters <= 0xffffff4) {
     90 	fs->fat_type = FAT28;
     91 	minfatsize = fs->endcluster << 2;
     92     } else
     93 	goto barf;		/* Impossibly many clusters */
     94 
     95     minfatsize = (minfatsize + LIBFAT_SECTOR_SIZE - 1) >> LIBFAT_SECTOR_SHIFT;
     96 
     97     if (minfatsize > fatsize)
     98 	goto barf;		/* The FATs don't fit */
     99 
    100     if (fs->fat_type == FAT28)
    101 	fs->rootcluster = read32(&bs->u.fat32.bpb_rootclus);
    102     else
    103 	fs->rootcluster = 0;
    104 
    105     return fs;			/* All good */
    106 
    107 barf:
    108     if (fs)
    109 	free(fs);
    110     return NULL;
    111 }
    112 
    113 void libfat_close(struct libfat_filesystem *fs)
    114 {
    115     libfat_flush(fs);
    116     free(fs);
    117 }
    118