https://github.com/njaard/cow
A Copy-on-write filesystem (fuse)
https://github.com/njaard/cow
Last synced: 6 months ago
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A Copy-on-write filesystem (fuse)
- Host: GitHub
- URL: https://github.com/njaard/cow
- Owner: njaard
- Created: 2015-10-22T18:21:43.000Z (almost 10 years ago)
- Default Branch: master
- Last Pushed: 2015-10-23T20:06:06.000Z (almost 10 years ago)
- Last Synced: 2025-03-25T08:11:11.510Z (7 months ago)
- Language: C++
- Homepage:
- Size: 148 KB
- Stars: 6
- Watchers: 1
- Forks: 0
- Open Issues: 0
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Metadata Files:
- Readme: README.md
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README
# STATUS
Currently working!
Well, the tests, at least.
# Introduction
This is a FUSE-based filesystem that implements Copy-on-Write semantics over an existing directory structure.
What you do is use the `cow_fuse` binary to mount the filesystem atop a directory structure that already
exists. `cow_fuse` then replaces that filesystem with an identical one. Any changes made to that filesystem,
be it the contents modified, file modes changed, files renamed, or new files added are recorded, with the original
directory structure still accessible.
This software is still in development, so not only do I think there's bugs, I can nearly assure you of some.
# Requirements
* Your compiler must support C++11, gcc 4.9 is sufficient, and probably some older versions will
work too.
* sqlite3 is required, as it is used to store history data.
* Linux; no other OS is supported, although porting to any Unix-like OS with FUSE support
should be something between trivial and easy.
# Usage
So let's say you have a collection of files in a directory called "data"; we can create a COW-version of
data called "data2":
## Mounting
cow_fuse data
Now, the directory `data` is replaced with a directory that keeps track of the original version. When you unmount,
you'll see a directory named `data/.cow` that contains information used for tracking the older version.
## Features
The directory `data` works like any directory, except it's slower and has the COW feature. Inside `data` is
another directory named `.original` which doesn't get listed, even with `ls -a`. The directory `.original`
contains all files as they were before any changes were made to `data`.
# Future Plans
* The GNU command `cp` has the option `--reflink=always` which is used for making
Copy-On-Write copies of whole files; this should be supported.
* It'd be nice to provide a "snapshot" command to allow you to store any number of states
of the directory structure.
# Regression Testing
Automated tests are included, they check various aspects of the software's stability. I
generally update them as I add new features, and I generally run the tests very frequently
and before committing.
# Bugs
* Buggy in general. Don't trust it yet!
* Since Linux provides no facility for filesystem atomicity, failures can cause corruptions
in the snapshots, since a modification to the current file may be written to disk
before the history file is written. If a system failure occurs between these two events,
then the snapshot will be wrong. Linux doesn't really ensure an order of writes which is highly
unfortunate. The only way to fix this is for the current version to be stored in a special
format and the history to remain as real filesystem entries.
* If you modify a file so that it is the same as the original, some garbage collection can
be done there.