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The BitKeeper non-compete clause

Certain subjects return to these pages over and over again; one of those, certainly, is the BitKeeper source management system. Despite concerns about its proprietary nature, BitKeeper has become the tool of choice for many Linux kernel developers. Those who are concerned about BitKeeper use for kernel development found new flame fuel in a previously unnoticed clause in the BitKeeper license, version 1.38, which reads:

The purpose of this clause is to say "you can use BitKeeper free of charge, but only if you are not using it to develop a competitor to BitKeeper." It is arguably a reasonable licensing clause; regardless of what one thinks of BitKeeper or proprietary software in general, BitMover can not be expected to willingly provide its tools for the purpose of creating new competition.

And BitMover does fear this competition. Many years of effort went into the development of BitKeeper and the associated business; the creation of a suitably capable free replacement could wipe out that investment in a short time. BitMover founder Larry McVoy believes that the free software community is not capable of creating from scratch a source management system of BitKeeper's quality and with BitKeeper's innovations. He does, however, think it could produce a clone that, while inferior, is good enough to cost BitMover a lot of business. Coming up with ideas in the first place is expensive; copying them is far easier. BitMover wants the space to earn something from its (expensive) efforts to create BitKeeper; it also wants to be able to develop the product into a far more capable tool, a task requiring, they think, about four years. They have stated their intention to fight back with every weapon at their disposal - including copyright and patents - against anybody who threatens their ability to carry out that plan.

Is all this a problem for free software and the Linux kernel? It could be, but probably not on the scale that some people fear. The immediate concern with the clause quoted above is that a number of free software developers and companies do deal with other source management systems. In the case of developers, the situation is fairly clear: if you work on a free source management system, BitKeeper is not available to you. To emphasize the point, Larry McVoy publicly told Ben Collins, a kernel FireWire driver developer (and Subversion hacker) that he could not use BitKeeper:

Ben's kernel work will not be affected, since he was not using BitKeeper for that project. Other kernel developers could eventually run afoul of this rule as well, however. For example, the ReiserFS team has no end of ambitious plans for its filesystem; some of them, such as version management, begin to push into BitKeeper's turf. Larry told us that, in his opinion, it was "very likely" that ReiserFS would eventually cross the line and become a BitKeeper competitor; at that point its developers would be unable to use BitKeeper.

That is about as far as it goes, however. The license, says Larry, went too far by excluding anybody whose employer works on source management systems. The next "debugging" release of the license will tighten that term so that it only affects developers working directly on source management, and, perhaps, those very close to them. Thus, for example, Red Hat developers will not lose their access to BitKeeper just because Red Hat puts some patches into CVS. It is also BitMover's position the Linux kernel developers as a whole will not lose their BitKeeper access even if Linus merges a version of ReiserFS which costs the ReiserFS team its access.

In evaluating the whole BitKeeper controversy, it is worth remembering a few things. One is that BitMover could have avoided all this pain simply by never giving gratis access to its product. Other vendors of commercial source management systems do not make their products available for free-of-charge use, and they are not routinely flamed the way BitMover is. BitMover, instead, has chosen to make its product freely available to groups developing free software. Kernel development has benefitted from this gift in a number of ways:

• The capabilities of BitKeeper are much appreciated by developers who choose to use it. BitKeeper really does make a lot of things easier, especially in a distributed, multi-developer environment.

• Linus is merging patches at a tremendous rate, and appears to be far less stressed than before. Patches still get dropped, but on a much smaller scale. The process, by all appearances, is working more smoothly than it has in a long time.

• Anybody who is interested can see the state of Linus's development tree in near real time. There is no longer any need to wait for prepatches or full releases. Thanks to BitKeeper, a new development kernel is released many times a day. As an added bonus, Linus is now able to post automatic changelogs as well, eliminating the need to read through each release to see what patches were included.

It is also worth pointing out that nobody has been forced to use BitKeeper. Many top-tier kernel developers have chosen not to use it, and they have not had to change their ways of working. Getting repositories and patches into and out of BitKeeper is easy by design; BitKeeper has a stated "no lockin" policy. It is not even necessary to use BitKeeper to keep track of Linus; several sites (like this one) provide frequent access to the updates in his tree.

In other words, the adoption of BitKeeper has brought good things to anybody who uses the Linux kernel. This has happened free of charge, with no visible costs of any significance. Except, perhaps, for the time lost in flame wars. Access to BitKeeper is a gift that its creator was under no obligation to make. It is unfortunate that some members of the community expend so much effort criticising those who have made that gift. It is hard to see how the free software community would be better off if BitKeeper were withdrawn.

All this is not to say that there is no reason for vigilance and concern. The denial of access to some developers is a discriminatory action, to say the least. If Larry McVoy (or his board of directors) wakes up hung over one morning and decides to end free access to BitKeeper, the show is over. Larry is uninclined to do that - he has maintained free access despite the constant flames because he wants to support the kernel project. But Larry could have an unfortunate encounter with a bus (though, as Linus has pointed out, buses are rare in California), or BitMover could be acquired by another company; in either case, the new management could make changes to the license. The BitKeeper binary does not come with source; it could be doing no end of evil things and it would be difficult for people to know. Currently, BitKeeper makes it easy to extract all data and metadata from a repository; moving an entire repository into a different source management system is an easy task. Linus also uses the BitKeeper interfaces to export patches and tarballs in the same way he always has. Future versions of BitKeeper, however, could quietly shift over to a closed format that is harder to escape from.

And so on. These are issues that come up with any proprietary package, and they are certainly no worse than the issues raised by that other proprietary source management platform which is even more heavily used in the free software community: SourceForge. In the end, people who use software should always look at the license, and not use a particular package if the license is not to their taste. In the case of BitKeeper, those who chose not to use it are no worse off than they were before, and an easy path is open should a quick evacuation to another source management system be required. BitKeeper is worth watching; one never knows where a company might decide to go tomorrow. But the situation at the moment is not that bad.

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Update on LWN and subscriptions

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