I am reading this thread for a long long time now and have to say that you did a great job already!!
I read the source code for the cfs
Have you read only the code in the Rockbox sources or also the standalone programs I made (which are usable on a PC)?
and it seems reasonable to understand but now I need a test file to look further into the structure of the vfat system. I downloaded the one on the wiki but that does not seem to contain the vfat directory?
quetzalcoatl said something about a 122,5 mb file but I can't find that file anywhere. Is it available?
I can provide 2 GZIP'ed 30GB filesystems (raw copies of my ZVM HDD, it compresses to about 40MB). Of course you'll need quite some space to unpack them, unless you use sparse files (a feature that exists on some Linux file systems and also in NTFS, but I've only tested it on Linux).
Notes for file 1:
- I filled the 'virtual' disk with 0x11
- when the Creative OS formatted the 'virtual' disk, it added a standard FAT header in it; so the OS knows how to 'format' drives as FAT
- the file unpacks as a 30GB disk dump
- as mediafire detected a virus (?), I encrypted the file; to decrypt it you'll need openssl:
openssl enc -in disk_dump.enc -out disk_dump.dec.gz -k quetzalcoatl -d -blowfish
Notes for file 2:
- I filled the 'virtual' disk filled with 0x0 and then I formatted it as FAT
- same notes as other file (30GB HDD & encrypted with same key)
illustrates how to unzip the files to a sparse file on Linux (meaning the file will appear to be 30GB big, but will only take in about 40MB of space)