1,短目录和长目录：
短目录和长目录都是放在Data region里的，一个directory entry占用32byte，具体参考下表：
Short directory entry
|
Name |
Offset (byte) |
Size (bytes) |
Description |
|
DIR_Name |
0 |
11 |
Short name. |
|
DIR_Attr |
11 |
1 |
File attributes: ATTR_READ_ONLY 0x01 ATTR_HIDDEN 0x02 ATTR_SYSTEM 0x04 ATTR_VOLUME_ID 0x08 ATTR_DIRECTORY 0x10 ATTR_ARCHIVE 0x20 ATTR_LONG_NAME ATTR_READ_ONLY | ATTR_HIDDEN | ATTR_SYSTEM | ATTR_VOLUME_ID The upper two bits of the attribute byte are reserved and should always be set to 0 when a file is created and never modified or looked at after that. |
| DIR_NTRes | 12 | 1 | Reserved for use by Windows NT. |
| DIR_CrtTimeTenth | 13 | 1 | Millisecond stamp at file creation time. |
| DIR_CrtTime | 14 | 2 | Time file was created. |
| DIR_CrtDate | 16 | 2 | Date file was created. |
| DIR_LstAccDate | 18 | 2 | Last access date. |
| DIR_FstClusHI | 20 | 2 | High word of this entry’s first cluster number (always 0 for a FAT12 or FAT16 volume). |
| DIR_WrtTime | 22 | 2 | Time of last write. |
| DIR_WrtDate | 24 | 2 | Date of last write. |
| DIR_FstClusLO | 26 | 2 | Low word of this entry’s first cluster number. |
| DIR_FileSize | 28 | 4 |
32-bit DWORD holding this file’s size in bytes. 所以FAT32支持文件的最大大小为4G |
DIR_Name不能包含以下字符：
1， 任何小于0X20值的字符，除了0x05（0X05代表的含义是该目录entry可以被重新使用，删除一个文件的时候用0x05来覆盖DIR_Name[0,如果DIR_Name[0]的值为0，表示该entry可以被使用~之前没有被使用过）
2，0x22, 0x2A, 0x2B, 0x2C, 0x2E, 0x2F, 0x3A, 0x3B, 0x3C, 0x3D, 0x3E, 0x3F, 0x5B, 0x5C, 0x5D, and 0x7C.
Shaort name举例如下：
“foo.bar” -> “FOO BAR”
“FOO.BAR” -> “FOO BAR”
“Foo.Bar” -> “FOO BAR”
“foo” -> “FOO “
“foo.” -> “FOO “
“PICKLE.A” -> “PICKLE A “
“prettybg.big” -> “PRETTYBGBIG”
“.big” -> illegal, DIR_Name[0] cannot be 0x20
Data format:
a date relative to the MS-DOS epoch of 01/01/1980
|
Bits |
Description |
|
15-9 |
Year (0 = 1980, 127 = 2107) |
|
8-5 |
Month (1 = January, 12 = December) |
|
4-0 |
Day (1 - 31) |
Time format:
The valid time range is from Midnight 00:00:00 to 23:59:58
|
Bits |
Description |
|
15-11 |
Hours (0-23) |
|
10-5 |
Minutes (0-59) |
|
4-0 |
Seconds/2 (0-29) |
long directory entry
|
Name |
Offset (byte) |
Size (bytes) |
Description |
|
LDIR_Ord |
0 |
1 |
The order of this entry in the sequence of long dir entries associated with the short dir entry at the end of the long dir set.
|
|
LDIR_Name1 |
1 |
10 |
Characters 1-5 of the long-name sub-component in this dir entry. |
|
LDIR_Attr |
11 |
1 |
Attributes - must be ATTR_LONG_NAME |
|
LDIR_Type |
12 |
1 |
If zero, indicates a directory entry that is a sub-component of a long name. NOTE: Other values reserved for future extensions. Non-zero implies other dirent types. |
|
LDIR_Chksum |
13 |
1 |
Checksum of name in the short dir entry at the end of the long dir set. |
|
LDIR_Name2 |
14 |
12 |
Characters 6-11 of the long-name sub-component in this dir entry. |
|
LDIR_FstClusLO |
26 |
2 |
Must be ZERO. This is an artifact of the FAT "first cluster" and must be zero for compatibility with existing disk utilities. It's meaningless in the context of a long dir entry. |
|
LDIR_Name3 |
28 |
4 |
Characters 12-13 of the long-name sub-component in this dir entry. |
Example:
当一个文件名字是"The quick brown.fox". 以下的表格说明了它是如何存放在directory entry里的。
FAT32对文件名以及文件路径的限制：
1， 短目录名可以包含任何字母数字以及下面的字符：
$ % ' - _ @ ~ ` ! ( ) { } ^ # &
2， 长目录名不能包含如下字符
+ , ; = [ ]
3， 短目录名路径最大长度是8+3，端目录完整路径长度最大为80（包含最后的结束NUL字符）
4， 长目录完整路径最大为255（不包含最后的NUL字符）
5， 长目录entry是通过UNICODE来放具体名字的字符的，2个byte对应一个字符，区分大小写。
6， 短目录entry是不区分大小写的。