Simple Forth File System based upon the BLOCK word-set

• Author: Richard James Howe
• Email: mailto:[email protected]
• License: The Unlicense / Public Domain
• Repo: https://github.com/howerj/ffs

This is a simple Forth block based file system. See the Forth file ffs.fth for more information including documentation.

The file system provides a word-set that allows a user to interact with a disk image like you would with a DOS based system.

This project works under https://gforth.org/ and also SUBLEQ eForth (see https://github.com/howerj/subleq).

Some quick notes and limitations:

• Files consist of non-contiguous Forth Blocks.
• Files still consist of Forth Blocks, so are multiples of 1024 bytes in size.
• The maximum file system size is roughly 64MiB.
• The maximum number of files per directory is 31.
• The file system is reliant on the Forth Block word-set and should run on even the most spartan Forth system so long as it is present.
• File names are limited to 16 bytes in size.
• Some commands include; edit, exe, ls, rm, rmdir, mkdir, cd, pwd, tree, cp, rename, cat, hexdump, more, df, halt, fdisk, and stat.
• Full file path parsing is not available and most commands operate only using the current working directory. For example you cannot rm a/b/c, you would need to cd a, cd b and then call rm c. This is not a limitation of the file system but the tools built upon it. Some utilities can parse "." for the current directory and ".." for the next directory up such as "mv" and "cd" but most cannot.
• The file system is designed to run as a single user system, there is no locking and global variables are used.
• Only one file system can be mounted at a time.
• Some commands are line oriented, others have block oriented analogues such as "cat" (line oriented) and "bcat" (block oriented). The block oriented utilities expect the files given to them to formatted as a Forth Block would be.
• There is no redundant FAT block data structure like in FAT-12/FAT-16/FAT-32.
• Low memory usage: The file system uses kilobytes of data (and can be further reduced if features like editing are not required). A handful of variables and buffers are used, along with the Forth Block system (a Block System with a single buffer would work).

Examples

The following section contains a few examples of how to use the file system and associated commands. To run the SUBLEQ eForth examples you will need make and a C compiler installed and on your PATH.

GForth

An example session:

mkdir example
cd example
pwd
edit test.fth \ Start editor commands
+ .( FIRST BLOCK ) cr
    + .( FIRST BLOCK, SECOND LINE ) cr
n
+ .( SECOND BLOCK ) cr
s
q     \ Back to "DOS"
ls
exe test.fth
df
rm test.fth
ls

SUBLEQ eForth

To run the SUBLEQ eForth system you will need to type:

make disk

This will make a bootable disk image that will work with the SUBLEQ VM. It will take a while to do so.

Instead of saving to a file called ffs.fb the disk image disk.dec will be updated after exiting from the SUBLEQ VM cleanly.

The SUBLEQ VM File System can only allocate from a pool of about 61 blocks, there are special files that are created, such as [KERNEL] that allow file system access to the SUBLEQ eForth image.

Example Sessions

An example session recorded with ttyrec (all shorter than they should be because of problems converting the recording to a GIF):

And another:

And another:

References

• https://github.com/howerj/subleq
• https://en.wikipedia.org/wiki/File_Allocation_Table