vfat.txt 10 KB

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  1. USING VFAT
  2. ----------------------------------------------------------------------
  3. To use the vfat filesystem, use the filesystem type 'vfat'. i.e.
  4. mount -t vfat /dev/fd0 /mnt
  5. No special partition formatter is required. mkdosfs will work fine
  6. if you want to format from within Linux.
  7. VFAT MOUNT OPTIONS
  8. ----------------------------------------------------------------------
  9. umask=### -- The permission mask (for files and directories, see umask(1)).
  10. The default is the umask of current process.
  11. dmask=### -- The permission mask for the directory.
  12. The default is the umask of current process.
  13. fmask=### -- The permission mask for files.
  14. The default is the umask of current process.
  15. codepage=### -- Sets the codepage number for converting to shortname
  16. characters on FAT filesystem.
  17. By default, FAT_DEFAULT_CODEPAGE setting is used.
  18. iocharset=name -- Character set to use for converting between the
  19. encoding is used for user visible filename and 16 bit
  20. Unicode characters. Long filenames are stored on disk
  21. in Unicode format, but Unix for the most part doesn't
  22. know how to deal with Unicode.
  23. By default, FAT_DEFAULT_IOCHARSET setting is used.
  24. There is also an option of doing UTF-8 translations
  25. with the utf8 option.
  26. NOTE: "iocharset=utf8" is not recommended. If unsure,
  27. you should consider the following option instead.
  28. utf8=<bool> -- UTF-8 is the filesystem safe version of Unicode that
  29. is used by the console. It can be enabled for the
  30. filesystem with this option. If 'uni_xlate' gets set,
  31. UTF-8 gets disabled.
  32. uni_xlate=<bool> -- Translate unhandled Unicode characters to special
  33. escaped sequences. This would let you backup and
  34. restore filenames that are created with any Unicode
  35. characters. Until Linux supports Unicode for real,
  36. this gives you an alternative. Without this option,
  37. a '?' is used when no translation is possible. The
  38. escape character is ':' because it is otherwise
  39. illegal on the vfat filesystem. The escape sequence
  40. that gets used is ':' and the four digits of hexadecimal
  41. unicode.
  42. nonumtail=<bool> -- When creating 8.3 aliases, normally the alias will
  43. end in '~1' or tilde followed by some number. If this
  44. option is set, then if the filename is
  45. "longfilename.txt" and "longfile.txt" does not
  46. currently exist in the directory, 'longfile.txt' will
  47. be the short alias instead of 'longfi~1.txt'.
  48. quiet -- Stops printing certain warning messages.
  49. check=s|r|n -- Case sensitivity checking setting.
  50. s: strict, case sensitive
  51. r: relaxed, case insensitive
  52. n: normal, default setting, currently case insensitive
  53. shortname=lower|win95|winnt|mixed
  54. -- Shortname display/create setting.
  55. lower: convert to lowercase for display,
  56. emulate the Windows 95 rule for create.
  57. win95: emulate the Windows 95 rule for display/create.
  58. winnt: emulate the Windows NT rule for display/create.
  59. mixed: emulate the Windows NT rule for display,
  60. emulate the Windows 95 rule for create.
  61. Default setting is `lower'.
  62. <bool>: 0,1,yes,no,true,false
  63. TODO
  64. ----------------------------------------------------------------------
  65. * Need to get rid of the raw scanning stuff. Instead, always use
  66. a get next directory entry approach. The only thing left that uses
  67. raw scanning is the directory renaming code.
  68. POSSIBLE PROBLEMS
  69. ----------------------------------------------------------------------
  70. * vfat_valid_longname does not properly checked reserved names.
  71. * When a volume name is the same as a directory name in the root
  72. directory of the filesystem, the directory name sometimes shows
  73. up as an empty file.
  74. * autoconv option does not work correctly.
  75. BUG REPORTS
  76. ----------------------------------------------------------------------
  77. If you have trouble with the VFAT filesystem, mail bug reports to
  78. chaffee@bmrc.cs.berkeley.edu. Please specify the filename
  79. and the operation that gave you trouble.
  80. TEST SUITE
  81. ----------------------------------------------------------------------
  82. If you plan to make any modifications to the vfat filesystem, please
  83. get the test suite that comes with the vfat distribution at
  84. http://bmrc.berkeley.edu/people/chaffee/vfat.html
  85. This tests quite a few parts of the vfat filesystem and additional
  86. tests for new features or untested features would be appreciated.
  87. NOTES ON THE STRUCTURE OF THE VFAT FILESYSTEM
  88. ----------------------------------------------------------------------
  89. (This documentation was provided by Galen C. Hunt <gchunt@cs.rochester.edu>
  90. and lightly annotated by Gordon Chaffee).
  91. This document presents a very rough, technical overview of my
  92. knowledge of the extended FAT file system used in Windows NT 3.5 and
  93. Windows 95. I don't guarantee that any of the following is correct,
  94. but it appears to be so.
  95. The extended FAT file system is almost identical to the FAT
  96. file system used in DOS versions up to and including 6.223410239847
  97. :-). The significant change has been the addition of long file names.
  98. These names support up to 255 characters including spaces and lower
  99. case characters as opposed to the traditional 8.3 short names.
  100. Here is the description of the traditional FAT entry in the current
  101. Windows 95 filesystem:
  102. struct directory { // Short 8.3 names
  103. unsigned char name[8]; // file name
  104. unsigned char ext[3]; // file extension
  105. unsigned char attr; // attribute byte
  106. unsigned char lcase; // Case for base and extension
  107. unsigned char ctime_ms; // Creation time, milliseconds
  108. unsigned char ctime[2]; // Creation time
  109. unsigned char cdate[2]; // Creation date
  110. unsigned char adate[2]; // Last access date
  111. unsigned char reserved[2]; // reserved values (ignored)
  112. unsigned char time[2]; // time stamp
  113. unsigned char date[2]; // date stamp
  114. unsigned char start[2]; // starting cluster number
  115. unsigned char size[4]; // size of the file
  116. };
  117. The lcase field specifies if the base and/or the extension of an 8.3
  118. name should be capitalized. This field does not seem to be used by
  119. Windows 95 but it is used by Windows NT. The case of filenames is not
  120. completely compatible from Windows NT to Windows 95. It is not completely
  121. compatible in the reverse direction, however. Filenames that fit in
  122. the 8.3 namespace and are written on Windows NT to be lowercase will
  123. show up as uppercase on Windows 95.
  124. Note that the "start" and "size" values are actually little
  125. endian integer values. The descriptions of the fields in this
  126. structure are public knowledge and can be found elsewhere.
  127. With the extended FAT system, Microsoft has inserted extra
  128. directory entries for any files with extended names. (Any name which
  129. legally fits within the old 8.3 encoding scheme does not have extra
  130. entries.) I call these extra entries slots. Basically, a slot is a
  131. specially formatted directory entry which holds up to 13 characters of
  132. a file's extended name. Think of slots as additional labeling for the
  133. directory entry of the file to which they correspond. Microsoft
  134. prefers to refer to the 8.3 entry for a file as its alias and the
  135. extended slot directory entries as the file name.
  136. The C structure for a slot directory entry follows:
  137. struct slot { // Up to 13 characters of a long name
  138. unsigned char id; // sequence number for slot
  139. unsigned char name0_4[10]; // first 5 characters in name
  140. unsigned char attr; // attribute byte
  141. unsigned char reserved; // always 0
  142. unsigned char alias_checksum; // checksum for 8.3 alias
  143. unsigned char name5_10[12]; // 6 more characters in name
  144. unsigned char start[2]; // starting cluster number
  145. unsigned char name11_12[4]; // last 2 characters in name
  146. };
  147. If the layout of the slots looks a little odd, it's only
  148. because of Microsoft's efforts to maintain compatibility with old
  149. software. The slots must be disguised to prevent old software from
  150. panicking. To this end, a number of measures are taken:
  151. 1) The attribute byte for a slot directory entry is always set
  152. to 0x0f. This corresponds to an old directory entry with
  153. attributes of "hidden", "system", "read-only", and "volume
  154. label". Most old software will ignore any directory
  155. entries with the "volume label" bit set. Real volume label
  156. entries don't have the other three bits set.
  157. 2) The starting cluster is always set to 0, an impossible
  158. value for a DOS file.
  159. Because the extended FAT system is backward compatible, it is
  160. possible for old software to modify directory entries. Measures must
  161. be taken to ensure the validity of slots. An extended FAT system can
  162. verify that a slot does in fact belong to an 8.3 directory entry by
  163. the following:
  164. 1) Positioning. Slots for a file always immediately proceed
  165. their corresponding 8.3 directory entry. In addition, each
  166. slot has an id which marks its order in the extended file
  167. name. Here is a very abbreviated view of an 8.3 directory
  168. entry and its corresponding long name slots for the file
  169. "My Big File.Extension which is long":
  170. <proceeding files...>
  171. <slot #3, id = 0x43, characters = "h is long">
  172. <slot #2, id = 0x02, characters = "xtension whic">
  173. <slot #1, id = 0x01, characters = "My Big File.E">
  174. <directory entry, name = "MYBIGFIL.EXT">
  175. Note that the slots are stored from last to first. Slots
  176. are numbered from 1 to N. The Nth slot is or'ed with 0x40
  177. to mark it as the last one.
  178. 2) Checksum. Each slot has an "alias_checksum" value. The
  179. checksum is calculated from the 8.3 name using the
  180. following algorithm:
  181. for (sum = i = 0; i < 11; i++) {
  182. sum = (((sum&1)<<7)|((sum&0xfe)>>1)) + name[i]
  183. }
  184. 3) If there is free space in the final slot, a Unicode NULL (0x0000)
  185. is stored after the final character. After that, all unused
  186. characters in the final slot are set to Unicode 0xFFFF.
  187. Finally, note that the extended name is stored in Unicode. Each Unicode
  188. character takes two bytes.