{"id":19,"date":"2006-02-12T20:21:11","date_gmt":"2006-02-13T01:21:11","guid":{"rendered":"http:\/\/mattwork.potsdam.edu\/blog\/?p=19"},"modified":"2013-09-20T16:22:41","modified_gmt":"2013-09-20T20:22:41","slug":"copyfs-is-now-even-cooler","status":"publish","type":"post","link":"http:\/\/www.matthewgkeller.com\/blog\/2006\/02\/12\/copyfs-is-now-even-cooler\/","title":{"rendered":"CopyFS is now even cooler"},"content":{"rendered":"

[UPDATE<\/strong>: There is a newer version of CopyFS available<\/a>]<\/p>\n

Some backstory: I used to write a LOT of code in the C programming language. I used to be actively involved in numerous open-source programs that used C. Hell, I even co-authored a book<\/a> that was completely about C code, written in the format of the much-loved classic Lions’ Commentary on UNIX<\/a>, and available in 6 languages. That was “back then”. I’ve gotten spoiled with Perl, Java and C++ over the last half-decade and haven’t written more than trivial patches in C in … 6 years. I still read C fluently… But not so much on the writing.<\/p>\n

So going [almost] back to my programming roots, I took on a project that forced me to dive head-first back in C. And not just a wussy application… No sir. A filesystem. Some guys beta test backup software, and some guys use their laptop as a live debugger for filesystem enhancements.\u00c2\u00a0 Before I get into\u00c2\u00a0 the details of the software, let me say that I’ve\u00c2\u00a0 finally popped back into the world of seeing C solutions, and knowing exactly how to get what I want out of the code… I’m not at the level I’m at with Perl, where I can literally have a conversation with a person in the language itself, but my C-fu is, again, strong.
\nSo enough about me. CopyFS<\/a> is a FUSE<\/a> filesystem that supports file versioning. v1.0 is a pure copy-on-write filesystem. Anytime you make a change, it makes a copy. If you change the metadata of a file, it makes a copy. You can list all of the versions of a file, and make any version the “current” version very easy. It really is a great tool.
\nI’ve been using CopyFS for a while now in various venues, the most active of which is my Eclipse<\/a> development tree- Where nearly all of my Perl, Python, C++, Java… and now C code is developed. It allowed me to have my own little revision control system on my filesystem without the complicated mucking around with CVS\/SVN\/git\/etc. repositories.
\nAfter using it for the quite-a-while I have been, the lack of certain features became a little painful. As CopyFS is open source software, I could just complain that the software doesn’t do what I want, write a snotty post to a mailing list and assert the entitlement that others seem to believe they have just because they downloaded a piece of software… Or I could enhance it. I could solve my own problems.<\/p>\n

Problem 1: Text Diffs<\/h3>\n

By far, the largest problem I was having was determining WHICH of the 212 versions of a source file were the ones I wanted to revert too. Ok, I broke something in the latest version, where’s one that doesn’t have changes to that area? That was done with no core changes- just 90ish lines of additions and a couple changed lines in the fversion<\/span> userspace application- All Perl.<\/p>\n

Problem 2: Way too many versions<\/h3>\n

As I mentioned previously, any change to a file will trigger a copy. I have some files with hundreds<\/span> of versions. For some files, this is great. For others… For example a pre-linked object file, this is unnecessary. While the sum of the code additions necessary to add this into CopyFS was a mere 200 lines, it took me thousands<\/span> of lines of C over the past few weeks to get to that 200 lines. Using fversion<\/span>, you can now tell the CopyFS daemon you want to purge the oldest N <\/span>versions, or all versions, of a given file.<\/p>\n

In progress…<\/h3>\n