libfat/open.c

   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 }