# Void Filesystem

Just a dummy filesystem for learning.

## Virtual Filesystem (VFS)

Linux VFS allows us to write customize filesystem. The filesystem must be able to mount, other operations such as file read/write or folder creation/deletion can be customized.

A filesystem can be virtual, without a backed-up device. This is the case for, I guess, network file descriptors. For filesystem with a backed-up device, usually a block device, the underlying block device can be accessed by sb_bread to read a block.

Internally, a filesystem must provide a superblock, that will be used as a pointer to read files.

When a file is read, the inode of the file entry can be accessed. If we also keep the internal data of the file in `inode->i_private`, we can fetch that to read the file system through `sb_read(inode->sb)`.

## Run

```
sudo make voidfs
sudo insmod voidfs.ko

# create a dummy file block device
dd if=/dev/zero of=dummy.iso bs=4096 count=1
mkdir -p drive
sudo mount -t voidfs -o loop dummy.iso drive
sudo ls drive
sudo cat drive/dummyfile
```

## Goal

- Fully working filesystem
- Read from block device
- Encrypted filesystem

## Design

TO BE UPDATED

## References

[simplefs](https://github.com/sysprog21/simplefs)

[Linux Kernel Labs - File system drivers](https://linux-kernel-labs.github.io/refs/heads/master/labs/filesystems_part1.html)

[Linux Kernel Documentation](https://docs.kernel.org/filesystems/vfs.html)