More than 135 Linux kernel developers have signed a document in protest of vendors that create closed-source code modules for the kernel, calling the practice "harmful and undesirable."

The developers' statement stressed that they are speaking for themselves, and not any of their employers.

Although the issue of proprietary kernel modules is not new, the matter recently came to a head, according to the developers.

"We have just been receiving a constant stream of questions from companies asking how the Linux kernel developers feel about closed-source modules over the past year or so," reads an accompanying FAQ page. "This statement should be the definite answer for how a large majority of them feel with regards to this topic."

The site defines modules as bits of code that are often drivers but also serve other functions, such as security.

Users and businesses are forced to rely on the module's creator for support instead of the Linux community, and closed modules can also give those users "a very bad perception of how Linux works due to the documented instability of many common closed-source modules," the FAQ states.

Vendors should open source their modules because they will be optimized by going through the kernel review process, according to the developers.

Help is available for this process, as the Linux Driver Project group will write drivers for vendors at no charge, the site notes.

The Linux Foundation has also published a long essay espousing the benefits of developing device drivers by the Linux model.

It's unclear how much impact the developers' statement will have, one observer suggested.

"Certainly, it has to be put in perspective. The statements of the Linux kernel developers, while of interest to many technical audiences, are unlikely to significantly impact the business decisions of hardware manufacturers by themselves," said Stephen O'Grady, an analyst with Redmonk.

"What's interesting is that they felt the timing was right for this message. Part of it might be that certain vendors -- Intel most obviously -- have been working effectively on open-source drivers more and more of late," he added.

One person who signed the statement said there is an additional consideration.

"There's no real timing other than the fact that a lot of companies are getting into Linux development, especially in the mobile space, and we were worried that people would get stuck on the [closed-source] drivers model without [giving the open-source approach] a chance," said James Bottomley, chairman of the Linux Foundation's technical advisory board.