The Filesystem Table, or FST, is a file present in Wii U disk images and downloaded content that describes the folders and files contained in the title.
It seems to be based on the Wii's FST format, but an extra header/cluster section was added.
All numbers are big-endian.
The file is composed of four sections:
- the main header
- a number of secondary headers describing storage clusters
- a number of file and directory entries, beginning with the root directory
- a table of null-terminated names
Size: 0x20 bytes
|Magic||0x4||0x0||always 0x46535400 ("FST" and a null byte)|
|Secondary header size||0x4||0x4||(not sure)|
|Secondary header count||0x4||0x8||Number of secondary headers in the FST|
Each of these entries describe the position of data on disk. For downloaded content, each corresponds to one entry from the TMD.
Size: 0x20 each
|Title ID||8||8||Not in all entries, some are zeros.|
|Group ID||4||16||Not in all entries, some are zeros.|
Each of these represents a file or a directory.
Size: 0x10 each
|Type||1||0||Zero for file entries, non-zero for directory entries|
|Name Offset||3||1||Offset in bytes of the name of the file from the start of the nametable|
|Offset||4||4||Offset of the file in its storage cluster: usually in sectors (multiply by 32 for byte offset); may be in bytes if the 0x4 bit in flags is set|
|Size||4||8||Size of the file in bytes|
|Flags||2||12||0x4: offset is in bytes, not sectors; 0x440: data contains SHA-1 hash|
|Storage cluster index||2||14||an index to the list of secondary headers. Additionally, for downloaded content, same as the content ID (an index into the title metadata's list of files.)|
In this case, the size corresponds to the number of entries this directory contains, and the offset field corresponds to the parent directory's offset.
Table of null-terminated filenames.
https://code.google.com/p/cdecrypt/source/browse/trunk/main.cpp - Crediar's CDecrypt tool that can parse FSTs from downloaded content
https://github.com/CarlKenner/dolphin/blob/WiiU/Source/Core/DiscIO/FileSystemWiiU.cpp - A fork of Dolphin by CarlKenner that can read WiiU disk images.
http://blog.delroth.net/2011/06/reading-wii-discs-with-python/ - some information on the Wii's FST format