Versioning File System

Versioning File System (uninterestingly abbreviated VFS) is a simple user-space file system implemented on top of FUSE with the aid of Bazil , written in Golang. Development on this project was started as means to learn more about the way Linux handles file systems, while at the same time answering a personal need of an easy to understand, transparent versioning file system for data backup. Although it should not yet be considered to be production ready, VFS is already usable in its current state.

Design

My goal was to build file system which could handle changes to file data and directory structure between mount cycles, in a simple, transparent way. I wanted to avoid storing version information in binary blobs, which are completely incomprehensible to the user. I strongly believed that the user should not be locked into a versioning scheme that prevented trivial migration or export of data. As such, versioned file data is stored in timestamped directories on a host file system (with minimal metadata stored in a human-readable format).

Each version consists of a root node and child nodes that represent modified files or directories for that version; unmodified data is not duplicated between versions. Other information (such as records about file and directory deletions) are stored in a JSON file next to the version root. Although VFS provides a mechanism for enumerating and mounting specific snapshots, the user is capable of browsing the version data directly if they choose to do so.

Installation

If you already have the Go environment and toolchain set up, you can get the latest version by running:

go get github.com/FooSoft/vfs

Users of Debian-based distributions can use godeb to quickly install the Go compiler on their machines.

Usage

Usage information can be seen by running VFS without command-line arguments:

Usage: ./vfs [options] database [mountpoint]

Parameters:
  -readonly=false: mount filesystem as readonly
  -version=0: version index (0 for head)

In the output above, the database parameter refers to a directory containing VFS versions; an empty directory is a valid database. The mountpoint parameter refers to the path on your system where the file system will be accessible (mounted).

Listing Volume Versions

Specifying a database path without the mount point will output a timestamped listing of available versions. This listing includes identifiers which can be used to specify a specific version to mount with the -version parameter. Note that only read-only mounting is possible of prior versions.

version: 1  time: 2015-06-19 11:14:13 +0900 JST
version: 2  time: 2015-06-20 13:08:04 +0900 JST
version: 3  time: 2015-06-22 15:12:09 +0900 JST
version: 4  time: 2015-06-24 12:41:43 +0900 JST

Mounting a Volume

1. Add yourself to the fuse user group if you are not added already (a requirement of FUSE). You can optionally skip this step by mounting the volume as the root user, but this is not recommended.
2. Execute ./vfs database_dir mountpoint_dir, using actual paths on your system to mount a volume. If you wish to provide an identifier for a specific version to mount, you may specify it with the -version parameter. Passing a non-zero value (zero indicates most recent version) will make the mount read-only. Explicit read-only mounting is also possible by setting the -readonly switch.
3. When you are finished using the volume, unmount it via the fusermount -u mountpoint_dir command.