Introduction to FUSE

FUSE is an interface that allows users to implement filesystems without needing to touch the bulky kernel code. While we might have heard about ext4 or btrfs, we too can develop our own filesystems!

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About FUSE

FUSE = Filesystem in USErspace

  • filesystem implementation runs in userspace
    • implementation written in a language of user's choice (eg. Python)
    • implementation runs as a normal script or application
  • FUSE module provides a bridge from filesystem implementation to kernel interface

FUSE has 3 major components:

  • kernel module fuse.ko
  • userspace library libfuse
  • a mount utility

FUSE support on your system

The relevant kernel module, fuse.ko is shipped since Linux version 2.6.14, so any FUSE based filesystem implementation can be assumed to work across virtually all Linux systems as of now.

The presence of FUSE kernel module can be checked on any Linux system.

[lain@wired ~]$ lsmod | grep fuse
fuse                  212992  5

[lain@wired ~]$ pkg-config --list-all | grep ^fuse
fuse3                          fuse3 - Filesystem in Userspace
fuse                           fuse - Filesystem in Userspace

How does a virtual filesysetm with FUSE work?

  • FUSE library knows about the basic list of operations on filesystems
  • the implementation is expected to provide definition for these basic methods
  • whenever system performs one of the filesystem operations, FUSE module refers the implementation code for knowing how to service request

Why userspace?

  • ability to utilize the userspace stack
    • python libraries
    • interact with desktop environment
    • interact with network resources
  • don't touch the kernel if not needed

Where is FUSE being utilized?

  • NTFS-3G uses FUSE to mount and read NTFS drives on Linux, FreeBSD, macOS and other operating systems
  • gocryptfs provides an encrypted overlay filesystem
  • google-drive-ocamlfuse lets you mount your Google Drive onto a local folder and browse/edit files
  • WikipediaFS let you view and exit MediaWiki articles from your local file browser and text editor