According to the SFC (Software Freedom Conservancy), a nonprofit organization hosting a variety of open source projects, VMware is facing a legal battle.

The SFC claims VMware is using the Linux kernel without respecting the terms of its copyright license, the GPL. As such, the group is standing behind developer Christoph Hellwig and is providing a grant to fund his action as he takes the virtualization giant to court in Hamburg, Germany.

Hellwig is a part of the Conservancy's GPL Compliance Project for Linux Developers. Since joining it in 2012, he has spent a great deal of time investigating VMware's use of both the Busybox command shell and the Linux kernel in its products.

Unlike commercial litigants, the Conservancy neither seeks profit from litigation nor uses it early. The organization's FAQ explains:

Neither Conservancy nor [Hellwig] takes this action lightly nor without exhausting every other possible alternative first. This lawsuit is the outgrowth of years of effort to convince VMware to comply with GPL.

As with similar activities conducted by the FSF (Free Software Foundation), the SFC's goal is to see breaches of the terms of the GPL cured and the full source code the license requires made publicly available. The SFC's usual approach is to contact companies privately to tell them there's a problem; in many cases, that's enough for the problem to be fixed. Failure to make the source code available is often an oversight, and the GPL is easy to satisfy -- as long as you actually want to publish the source code.

VMware has responded positively to such approaches in the past. When the SFC approached VMware in 2011 and asked it to make the source of Busybox available, the company responded positively. It was during that process that the SFC discovered another, much more significant issue. The Conservancy and Hellwig specifically assert that:

VMware has combined copyrighted Linux code, licensed under GPLv2, with their own proprietary code called "vmkernel" and distributed the entire combined work without providing nor offering complete, corresponding source code for that combined work under terms of the GPLv2.

After an extended negotiation, the situation has hardened. While releasing the source to something marginal is easy, the source code involved here is for VMware's ESXi product -- not something the company would want to publish. VMware claims there's no breach of the GPL and it's in full compliance without releasing further source code, while the SFC continues to assert that's incorrect. A VMware spokesperson told me:

We believe the lawsuit is without merit, and that we look forward to prevailing on all issues through the judicial process in Germany. VMware is an active participant and has a long-standing commitment to the free and open source software community. VMware dedicates considerable resources to ensure that its use of open source software is compliant with license agreements.

This is clearly not a simple case of accidental noncompliance -- nor one of straightforward and willful abuse, as both the SFC and the FSF imply. It's likely that the root of the dispute is a difference in the interpretation of the GPL, combined with the actions of developers following that interpretation over time.

At first glance, this seemed like a conflict over "module loading." Vendors commonly write code their legal teams tell them will "insulate" them from the GPL so that they can use Linux drivers in proprietary code. This is a controversial topic among free software advocates, and a lawsuit clarifying the effectiveness of that strategy would be helpful.

Unfortunately, it may not be so simple. It looks like VMware started out originally with an insulating layer to allow its kernel to use unmodified Linux drivers. But analysis published by LWN (sadly paywalled) suggests to me that, while this may have been where VMware started, code from GPL-licensed modules may have migrated into the "insulation layer."

The case is being conducted in Germany, where Hellwig lives and where expert legal representation from GPL enforcement veteran Till Jaeger is available. All the same, it will have a global effect on VMware and on other users of the GPL, both as a test of the license itself and of the role assumed by the SFC in interpreting it. While a victory for the SFC might accelerate the trend away from strong copyleft licensing by corporate adopters, hopefully the outcome will bring clarity to interpreting the GPL that will enhance open source adoption.