Wednesday Nov 04, 2009

OSCON 2009: FreeBSD

The last "people" talk that I went to at OSCON was Marshall Kirk McKusick's talk "Building and Running an Open-Source Community". I was interested in this talk for a couple reasons. First, I don't know much about how the BSD communities work, and I'm always interested in how large open-source communities do things. Second, I was at Berkeley during the time of the Computer Systems Research Group (CSRG). And while I got to know some of the CSRG staff, I was not directly involved with the development of Berkeley Unix. So I wanted to find out more about what was going on while I was there.

Kirk mentioned that the CSRG started up in the 1970s, after Bill Joy was already at Berkeley. At first, they didn't use a source code control system. Then around 1980 they started using SCCS. There are various reasons for using a source code control system, such as making it easy to review changes if a regression is discovered. For the CSRG, introducing SCCS enabled better productivity for the CSRG staff. Although they still reviewed all the changes that were checked in prior to a release, they could hand off some of the mechanics, such as merging patches and testing, to trusted committers.

This basic structure, with a core team, a group of committers, and a group of developers, is still used today for FreeBSD development. Kirk mentioned a couple details that I thought were interesting. In particular, he said that most developers don't want to be committers. This is usually because they don't want to be involved that much; they just have a change or two that they want to see made. Kirk also mentioned that committers are held to higher standards for things like email etiquette. And all changes must be reviewed by at least one other committer.

The FreeBSD core team is 9 people who are nominated from and elected by the committers every 2 years. They maintain the FreeBSD roadmap, they resolve conflicts between committers, and they admit and remove committers.

Kirk pointed out that people can contribute to FreeBSD in ways other than writing code. They can write documentation, they can do testing, they can do release engineering, and so forth. These people can be committers, too, and there's no relative weighting between code committers and other committers. This also means that these other folks can be elected to the core team. In fact, the latest election brought an advocacy/marketing committer onto the core team. At the time of the talk, there were 390 committers and around 6,000 developers.

FreeBSD does a stable .0 release every couple years. The stable branch has a 5-year lifetime and a binary compatibility guarantee. Minor (dot) releases happen on the stable branch every 6 months or so. Development happens on the trunk, and important bug fixes are merged into the stable branch. They use Subversion and provide a CVS mirror.

The pre-release freeze times vary: for a new stable branch it's about a month, and for a dot release it's about a week. I'm not sure how to compare those times with the times for OpenSolaris. For example, OpenSolaris freezes are gradual: first there's a period where only bug fixes are allowed in (no new features), then there's a period where only fixes for stopper bugs are allowed in. I wish I'd thought to ask Kirk for more details on how FreeBSD manages freezes.

One of the ways the BSD license is different from the GPL or the CDDL is that it lets people make proprietary changes to the code. Kirk said that this does happen, but those changes are usually specific to a particular product. Because they aren't generally interesting, the FreeBSD project probably wouldn't take the changes even if they were offered.


Random information that I hope will be interesting to Oracle's technical community. The views expressed on this blog are my own and do not necessarily reflect the views of Oracle.


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