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

Linux Kernel Labs - File system drivers

Linux Kernel Documentation