open.c

linux内核

#ident "$Id$"
/* ----------------------------------------------------------------------- *
 *   
 *   Copyright 2004 H. Peter Anvin - All Rights Reserved
 *
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation, Inc., 53 Temple Place Ste 330,
 *   Boston MA 02111-1307, USA; either version 2 of the License, or
 *   (at your option) any later version; incorporated herein by reference.
 *
 * ----------------------------------------------------------------------- */

/*
 * open.c
 *
 * Open a FAT filesystem and compute some initial values; return NULL
 * on failure.
 */

#include <stdlib.h>
#include "libfatint.h"
#include "ulint.h"

struct libfat_filesystem *
libfat_open(int (*readfunc)(intptr_t, void *, size_t, libfat_sector_t),
	    intptr_t readptr)
{
  struct libfat_filesystem *fs = NULL;
  struct fat_bootsect *bs;
  int i;
  uint32_t sectors, fatsize, minfatsize, rootdirsize;
  uint32_t nclusters;

  fs = malloc(sizeof(struct libfat_filesystem));
  if ( !fs )
    goto barf;
  
  fs->sectors = NULL;
  fs->read = readfunc;
  fs->readptr = readptr;

  bs = libfat_get_sector(fs, 0);
  if ( !bs ) 
    goto barf;

  if ( read16(&bs->bsBytesPerSec) != LIBFAT_SECTOR_SIZE )
    goto barf;

  for ( i = 0 ; i <= 8 ; i++ ) {
    if ( (uint8_t)(1 << i) == read8(&bs->bsSecPerClust) )
      break;
  }
  if ( i > 8 )
    goto barf;
  fs->clustsize  = 1 << i;	/* Treat 0 as 2^8 = 64K */
  fs->clustshift = i;
  
  sectors = read16(&bs->bsSectors);
  if ( !sectors )
    sectors = read32(&bs->bsHugeSectors);

  fs->end = sectors;
  
  fs->fat     = read16(&bs->bsResSectors);
  fatsize     = read16(&bs->bsFATsecs);
  if ( !fatsize )
    fatsize   = read32(&bs->u.fat32.bpb_fatsz32);
  
  fs->rootdir = fs->fat + fatsize * read8(&bs->bsFATs);
  
  rootdirsize = ((read16(&bs->bsRootDirEnts) << 5) + LIBFAT_SECTOR_MASK)
					    >> LIBFAT_SECTOR_SHIFT;
  fs->data    = fs->rootdir + rootdirsize;

  /* Sanity checking */
  if ( fs->data >= fs->end )
    goto barf;

  /* Figure out how many clusters */
  nclusters = (fs->end - fs->data) >> fs->clustshift;
  fs->endcluster = nclusters + 2;

  if ( nclusters <= 0xff4 ) {
    fs->fat_type = FAT12;
    minfatsize = fs->endcluster + (fs->endcluster >> 1);
  } else if ( nclusters <= 0xfff4 ) {
    fs->fat_type = FAT16;
    minfatsize = fs->endcluster << 1;
  }  else if ( nclusters <= 0xffffff4 ) {
    fs->fat_type = FAT28;
    minfatsize = fs->endcluster << 2;
  } else
    goto barf;			/* Impossibly many clusters */
  
  minfatsize = (minfatsize + LIBFAT_SECTOR_SIZE-1) >> LIBFAT_SECTOR_SHIFT;

  if ( minfatsize > fatsize )
    goto barf;			/* The FATs don't fit */

  if ( fs->fat_type == FAT28 )
    fs->rootcluster = read32(&bs->u.fat32.bpb_rootclus);
  else
    fs->rootcluster = 0;

  return fs;			/* All good */

 barf:
  if ( fs )
    free(fs);
  return NULL;
}

void libfat_close(struct libfat_filesystem *fs)
{
  libfat_flush(fs);
  free(fs);
}