phoenixfs

A filesystem implemented in userspace (using FUSE), inspired by the way Git is designed. Only works on Linux, since macOS implements userspace filesystems differently. Seamlessly versions files on save, without any additional machinery: traps save events in the editor, and writes out to a mount point, in the form of loose objects.

Dependencies

1. Zlib (>= 1.2)
2. FUSE (>= 2.6)
3. pkg-config (>= 0.25)
4. Linux kernel (>= 2.6.15)

Usage

For the first run, you need two directories:

1. A git directory where the data will be stored.
2. An empty directory to use as the mountpoint.

 $ cd /tmp
 $ mkdir gitdir mountp
 $ phoneixfs mount gitdir mountp

Use the mountpoint as you see fit. Data will be written to the gitdir on umount: you can use it for subsequent mounts.

Now, everything in mountpoint is versioned. To access older revisions of FILE, use FILE@REV syntax, where REV is the number of revisions in the past you want to access. For example:

 $ echo "hello" >file1
 $ echo "goodbye" >file1
 $ echo "another hello" >file1
 $ cat file1
 another hello
 $ cat file1@1
 goodbye
 $ cat file1@2
 hello

Finally, to umount:

 $ fusermount -u mountp

Technical documentation

Uses a B+ tree to keep track of the filesystem tree, and a modified version of packfile v3/ packfile index v2 for storing revision information.

• gitdir/.git/loose/ contains zlib-deflated versions of content blobs, named by the SHA-1 digest of the content.

• gitdir/fstree is a raw dump of the B+ tree in a custom format.

• gitdir/master.pack and gitdir/master.idx are the packfile and packfile index respectively. During an unmount, the files in gitdir/.git/loose/ are packed up, and an index is generated.

• /tmp/phoenixfs.log is the debug log

master.idx, master.pack, and fstree are enough to recreate the entire versioned filesystem. The files in gitdir/ and gitdir/.git/loose/ can be removed after unmount.

Notes on the filesystem tree:

(dr: directory record | fr: file record | vfr: versioned file record)

• dr just contains a name and node pointer referencing vfrs. drs are inserted directly into the root node.

• vfr contains the path of the file, a list of frs representing the various versions of the file (fixed at REV_TRUNCATE), and a HEAD pointer to keep track of the latest version of the file.

• The B+ tree is keyed by the CRC32 hash of the path of the vfr/ dr, a design decision inspired by Btrfs.

• An fr, vfr, and dr (corresponding to its path) are created when a new file is created on the filesystem. Empty directories are not tracked: no dr is created for empty directories.

Limitations

The following invocations don't work:

 $ cp file1@1 file1 # FILE@REV can't be treated like a file

Contributing

Simply fork the project on GitHub and send pull requests.