fs/fdos/fat.c

   1 /*
   2  * (C) Copyright 2002
   3  * Stäubli Faverges - <www.staubli.com>
   4  * Pierre AUBERT  p.aubert@staubli.com
   5  *
   6  * See file CREDITS for list of people who contributed to this
   7  * project.
   8  *
   9  * This program is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU General Public License as
  11  * published by the Free Software Foundation; either version 2 of
  12  * the License, or (at your option) any later version.
  13  *
  14  * This program is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  17  * GNU General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU General Public License
  20  * along with this program; if not, write to the Free Software
  21  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  22  * MA 02111-1307 USA
  23  */
  24
  25 #include <common.h>
  26 #include <config.h>
  27 #include <malloc.h>
  28
  29 #if defined(CONFIG_CMD_FDOS)
  30
  31 #include "dos.h"
  32 #include "fdos.h"
  33
  34
  35 /*-----------------------------------------------------------------------------
  36  * fat_decode --
  37  *-----------------------------------------------------------------------------
  38  */
  39 unsigned int fat_decode (Fs_t *fs, unsigned int num)
  40 {
  41     unsigned int start = num * 3 / 2;
  42     unsigned char *address = fs -> fat_buf + start;
  43
  44     if (num < 2 || start + 1 > (fs -> fat_len * SZ_STD_SECTOR))
  45         return 1;
  46
  47     if (num & 1)
  48         return ((address [1] & 0xff) << 4) | ((address [0] & 0xf0 ) >> 4);
  49     else
  50         return ((address [1] & 0xf) << 8) | (address [0] & 0xff );
  51 }
  52 /*-----------------------------------------------------------------------------
  53  * check_fat --
  54  *-----------------------------------------------------------------------------
  55  */
  56 static int check_fat (Fs_t *fs)
  57 {
  58     int i, f;
  59
  60     /* Cluster verification                                                  */
  61     for (i = 3 ; i < fs -> num_clus; i++){
  62         f = fat_decode (fs, i);
  63         if (f < FAT12_LAST && f > fs -> num_clus){
  64             /* Wrong cluster number detected                                 */
  65             return (-1);
  66         }
  67     }
  68     return (0);
  69 }
  70 /*-----------------------------------------------------------------------------
  71  * read_one_fat --
  72  *-----------------------------------------------------------------------------
  73  */
  74 static int read_one_fat (BootSector_t *boot, Fs_t *fs, int nfat)
  75 {
  76     if (dev_read (fs -> fat_buf,
  77                   (fs -> fat_start + nfat * fs -> fat_len),
  78                   fs -> fat_len) < 0) {
  79         return (-1);
  80     }
  81
  82     if (fs -> fat_buf [0] || fs -> fat_buf [1] || fs -> fat_buf [2]) {
  83         if ((fs -> fat_buf [0] != boot -> descr &&
  84              (fs -> fat_buf [0] != 0xf9 || boot -> descr != MEDIA_STD)) ||
  85             fs -> fat_buf [0] < MEDIA_STD){
  86             /* Unknown Media                                                 */
  87             return (-1);
  88         }
  89         if (fs -> fat_buf [1] != 0xff || fs -> fat_buf [2] != 0xff){
  90             /* FAT doesn't start with good values                            */
  91             return (-1);
  92         }
  93     }
  94
  95     if (fs -> num_clus >= FAT12_MAX_NB) {
  96         /* Too much clusters                                                 */
  97         return (-1);
  98     }
  99
 100     return check_fat (fs);
 101 }
 102 /*-----------------------------------------------------------------------------
 103  * read_fat --
 104  *-----------------------------------------------------------------------------
 105  */
 106 int read_fat (BootSector_t *boot, Fs_t *fs)
 107 {
 108     unsigned int buflen;
 109     int i;
 110
 111     /* Allocate Fat Buffer                                                   */
 112     buflen = fs -> fat_len * SZ_STD_SECTOR;
 113     if (fs -> fat_buf) {
 114         free (fs -> fat_buf);
 115     }
 116
 117     if ((fs -> fat_buf = malloc (buflen)) == NULL) {
 118         return (-1);
 119     }
 120
 121     /* Try to read each Fat                                                  */
 122     for (i = 0; i< fs -> nb_fat; i++){
 123         if (read_one_fat (boot, fs, i) == 0) {
 124             /* Fat is OK                                                     */
 125             fs -> num_fat = i;
 126             break;
 127         }
 128     }
 129
 130     if (i == fs -> nb_fat){
 131         return (-1);
 132     }
 133
 134     if (fs -> fat_len > (((fs -> num_clus + 2) *
 135                           (FAT_BITS / 4) -1 ) / 2 /
 136                          SZ_STD_SECTOR + 1)) {
 137         return (-1);
 138     }
 139     return (0);
 140 }
 141
 142 #endif