Path Names

Format of the path names

The format of path name on the FatFs module is similer to the filename specs of DOS/Windos as follows:

"[drive:][/]directory/file"

The FatFs module supports long file name (LFN) and 8.3 format file name (SFN). The LFN can be used when LFN feature is enabled (_USE_LFN > 0). The sub directories are separated with a \ or / in the same way as DOS/Windows API. Duplicated separators are skipped and ignored. Only a difference is that the logical drive is specified in a numeral with a colon. When drive number is omitted, the drive number is assumed as default drive (drive 0 or current drive).

Control characters ('\0' to '\x1F') are recognized as end of the path name. Leading/embedded spaces in the path name are valid as a part of the name at LFN configuration but they are recognized as end of the path name at non-LFN configuration. Trailing spaces and dots are ignored.

In default configuration (_FS_RPATH == 0), it does not have a concept of current directory like OS oriented file system. All objects on the volume are always specified in full path name that follows from the root directory. Dot directory names are not allowed. Heading separator is ignored and it can be exist or omitted. The default drive is fixed to drive 0.

When relative path feature is enabled (_FS_RPATH == 1), specified path is followed from the root directory if a heading separator is exist. If not, it is followed from the current directory of the drive set with f_chdir function. Dot names are also allowed for the path name. The default drive is the current drive set with f_chdrive function.

Path name_FS_RPATH == 0_FS_RPATH == 1
file.txtA file in the root directory of the drive 0A file in the current directory of the current drive
/file.txtA file in the root directory of the drive 0A file in the root directory of the current drive
The root directory of the drive 0The current directory of the current drive
/The root directory of the drive 0The root directory of the current drive
2:The root directory of the drive 2The current directory of the drive 2
2:/The root directory of the drive 2The root directory of the drive 2
2:file.txtA file in the root directory of the drive 2A file in the current directory of the drive 2
../file.txtInvalid nameA file in the parent directory
.Invalid nameThis directory
..Invalid nameParent directory of the current directory
dir1/..Invalid nameThe current directory
/..Invalid nameThe root directory (sticks the top level)

When option _STR_VOLUME_ID is specified, also pre-defined strings can be used as drive identifier in the path name instead of a numeral.


Unicode API

The path names are input/output in either ANSI/OEM code (SBCS/DBCS) or Unicode depends on the configuration options. The type of arguments which specify the file names are defined as TCHAR. It is an alias of char in default. The code set used to the file name string is ANSI/OEM specifid by _CODE_PAGE. When _LFN_UNICODE is set to 1, the type of the TCHAR is switched to WCHAR to support Unicode (UTF-16 encoding). In this case, the LFN feature is fully supported and the Unicode specific characters, such as ✝☪✡☸☭, can also be used for the path name. It also affects data types and encoding of the string I/O functions. To define literal strings, _T(s) and _TEXT(s) macro are available to select either ANSI/OEM or Unicode automatically. The code shown below is an example to define the literal strings.

 f_open(fp, "filename.txt", FA_READ);      /* ANSI/OEM string */
 f_open(fp, L"filename.txt", FA_READ);     /* Unicode string */
 f_open(fp, _T("filename.txt"), FA_READ);  /* Changed by configuration */


Volume Management

The FatFs module needs dynamic work area called file system object for each volume (logical drive). It is registered to the FatFs module by f_mount() function. By default, each logical drive is bound to the physical drive with the same drive number and an FAT volume on the drive is serched by auto detect feature. It loads boot sectors and checks it if it is an FAT boot sector in order of sector 0 as SFD format, 1st partition, 2nd partition, 3rd partition and 4th partition as FDISK format.

When _MULTI_PARTITION == 1 is specified by configuration option, each individual logical drive is bound to the partition on the physical drive specified by volume management table. The volume management table must be defined by user to resolve relationship between logical drives and partitions. Following code is an example of a volume management table.

Example: Logical drive 0-2 are tied to three pri-partitions on the physical drive 0 (fixed disk)
         Logical drive 3 is tied to an FAT volume on the physical drive 1 (removable disk)

PARTITION VolToPart[] = {
    {0, 1},     /* Logical drive 0 ==> Physical drive 0, 1st partition */
    {0, 2},     /* Logical drive 1 ==> Physical drive 0, 2nd partition */
    {0, 3},     /* Logical drive 2 ==> Physical drive 0, 3rd partition */
    {1, 0}      /* Logical drive 3 ==> Physical drive 1 (auto detection) */
};

relationship between logical drive and physical drive

There are some considerations on using _MULTI_PARTITION configuration.