mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-10 02:28:06 +11:00
79 lines
2.5 KiB
Markdown
79 lines
2.5 KiB
Markdown
# Using the filesystem
|
|
|
|
The Collapse OS filesystem (CFS) is a very simple FS that aims at implementation
|
|
simplicity first. It is not efficient or featureful, but allows you to get
|
|
play around with the concept of files so that you can conveniently run programs
|
|
targeting named blocks of data with in storage.
|
|
|
|
The filesystem sits on a block device and there can only be one active
|
|
filesystem at once.
|
|
|
|
Files are represented by adjacent blocks of `0x100` bytes with `0x20` bytes of
|
|
metadata on the first block. That metadata tells the location of the next block
|
|
which allows for block iteration.
|
|
|
|
To create a file, you must allocate blocks to it and these blocks can't be
|
|
grown (you have to delete the file and re-allocate it). When allocating new
|
|
files, Collapse OS tries to reuse blocks from deleted files if it can.
|
|
|
|
Once "mounted" (turned on with `fson`), you can list files, allocate new files
|
|
with `fnew`, mark files as deleted with `fdel` and, more importantly, open files
|
|
with `fopen`.
|
|
|
|
Opened files are accessed a independent block devices. It's the glue code that
|
|
decides how many file handles we'll support and to which block device ID each
|
|
file handle will be assigned.
|
|
|
|
For example, you could have a system with three block devices, one for ACIA and
|
|
one for a SD card and one for a file handle. You would mount the filesystem on
|
|
block device `1` (the SD card), then open a file on handle `0` with `fopen 0
|
|
filename`. You would then do `bsel 2` to select your third block device which
|
|
is mapped to the file you've just opened.
|
|
|
|
## Trying it in the emulator
|
|
|
|
The shell emulator in `tools/emul/shell` is geared for filesystem usage. If you
|
|
look at `shell_.asm`, you'll see that there are 4 block devices: one for
|
|
console, one for fake storage (`fsdev`) and two file handles (we call them
|
|
`stdout` and `stdin`, but both are read/write in this context).
|
|
|
|
The fake device `fsdev` is hooked to the host system through the `cfspack`
|
|
utility. Then the emulated shell is started, it checks for the existence of a
|
|
`cfsin` directory and, if it exists, it packs its content into a CFS blob and
|
|
shoves it into its `fsdev` storage.
|
|
|
|
To, to try it out, do this:
|
|
|
|
$ mkdir cfsin
|
|
$ echo "Hello!" > cfsin/foo
|
|
$ echo "Goodbye!" > cfsin/bar
|
|
$ ./shell
|
|
|
|
The shell, upon startup, automatically calls `fson` targeting block device `1`,
|
|
so it's ready to use:
|
|
|
|
> fls
|
|
foo
|
|
bar
|
|
> fopen 0 foo
|
|
> bsel 2
|
|
> getb
|
|
> puth a
|
|
65
|
|
> getb
|
|
> puth a
|
|
6C
|
|
> getb
|
|
> puth a
|
|
6C
|
|
> getb
|
|
> puth a
|
|
6F
|
|
> getb
|
|
> puth a
|
|
21
|
|
> fdel bar
|
|
> fls
|
|
foo
|
|
>
|