This DS library implementation the Linux ROMFS file system for reading a pre-made boot romdisk.
To create a romdisk image, you will need the program "genromfs". This program was designed for Linux but can compile under Cygwin.", included is a prebuilt mingw windows binary.
This was derived/ported from KOS 1.3.x from the Dreamcast KallistiOS .
included is a simple FS test which demonstrates reading a couple of files from the romdisk, and then it displays the directory structure.
for more information about using the filesystem checkout the fs.h file for the proper api calls, which are all very similiar to standard stdio calls.
Also include is some stdio newlib stubs that call the kosFS for better stdio support but so far I havent figure out how to port those into the existing devkitpro / libnds configuration.