fat.c 4.0 KB

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  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. #include <common.h>
  25. #include <config.h>
  26. #include <malloc.h>
  27. #include "dos.h"
  28. #include "fdos.h"
  29. /*-----------------------------------------------------------------------------
  30. * fat_decode --
  31. *-----------------------------------------------------------------------------
  32. */
  33. unsigned int fat_decode (Fs_t *fs, unsigned int num)
  34. {
  35. unsigned int start = num * 3 / 2;
  36. unsigned char *address = fs -> fat_buf + start;
  37. if (num < 2 || start + 1 > (fs -> fat_len * SZ_STD_SECTOR))
  38. return 1;
  39. if (num & 1)
  40. return ((address [1] & 0xff) << 4) | ((address [0] & 0xf0 ) >> 4);
  41. else
  42. return ((address [1] & 0xf) << 8) | (address [0] & 0xff );
  43. }
  44. /*-----------------------------------------------------------------------------
  45. * check_fat --
  46. *-----------------------------------------------------------------------------
  47. */
  48. static int check_fat (Fs_t *fs)
  49. {
  50. int i, f;
  51. /* Cluster verification */
  52. for (i = 3 ; i < fs -> num_clus; i++){
  53. f = fat_decode (fs, i);
  54. if (f < FAT12_LAST && f > fs -> num_clus){
  55. /* Wrong cluster number detected */
  56. return (-1);
  57. }
  58. }
  59. return (0);
  60. }
  61. /*-----------------------------------------------------------------------------
  62. * read_one_fat --
  63. *-----------------------------------------------------------------------------
  64. */
  65. static int read_one_fat (BootSector_t *boot, Fs_t *fs, int nfat)
  66. {
  67. if (dev_read (fs -> fat_buf,
  68. (fs -> fat_start + nfat * fs -> fat_len),
  69. fs -> fat_len) < 0) {
  70. return (-1);
  71. }
  72. if (fs -> fat_buf [0] || fs -> fat_buf [1] || fs -> fat_buf [2]) {
  73. if ((fs -> fat_buf [0] != boot -> descr &&
  74. (fs -> fat_buf [0] != 0xf9 || boot -> descr != MEDIA_STD)) ||
  75. fs -> fat_buf [0] < MEDIA_STD){
  76. /* Unknown Media */
  77. return (-1);
  78. }
  79. if (fs -> fat_buf [1] != 0xff || fs -> fat_buf [2] != 0xff){
  80. /* FAT doesn't start with good values */
  81. return (-1);
  82. }
  83. }
  84. if (fs -> num_clus >= FAT12_MAX_NB) {
  85. /* Too much clusters */
  86. return (-1);
  87. }
  88. return check_fat (fs);
  89. }
  90. /*-----------------------------------------------------------------------------
  91. * read_fat --
  92. *-----------------------------------------------------------------------------
  93. */
  94. int read_fat (BootSector_t *boot, Fs_t *fs)
  95. {
  96. unsigned int buflen;
  97. int i;
  98. /* Allocate Fat Buffer */
  99. buflen = fs -> fat_len * SZ_STD_SECTOR;
  100. if (fs -> fat_buf) {
  101. free (fs -> fat_buf);
  102. }
  103. if ((fs -> fat_buf = malloc (buflen)) == NULL) {
  104. return (-1);
  105. }
  106. /* Try to read each Fat */
  107. for (i = 0; i< fs -> nb_fat; i++){
  108. if (read_one_fat (boot, fs, i) == 0) {
  109. /* Fat is OK */
  110. fs -> num_fat = i;
  111. break;
  112. }
  113. }
  114. if (i == fs -> nb_fat){
  115. return (-1);
  116. }
  117. if (fs -> fat_len > (((fs -> num_clus + 2) *
  118. (FAT_BITS / 4) -1 ) / 2 /
  119. SZ_STD_SECTOR + 1)) {
  120. return (-1);
  121. }
  122. return (0);
  123. }