Re: RTLinux patent

[Barak Pearlmutter <bap@cs.unm.edu>]

> http://www.rtlinux.org/documents/faq.html#Q5
>
>    Q: What's the license? How much do I pay? What about the patent?
>
>    A: RTLinux is released under the GPL and can be freely used,
>    modified, and redistributed under the terms of that license. If
>    you modify RTLinux code, the new code is automatically governed by
>    the GPL. However, if you write your code as separate modules, then
>    the license for the modules is up to you: GPL, proprietary,
>    whatever. RTLinux is also governed by a license to use the base
>    RTLinux mechanism under U.S. Patent 5,995,745. The patent license
>    basically reinforces the GPL terms. There is no fee for using
>    RTLinux, for using your module/applications with RTLinux or for
>    using modified RTLinux code under the GPL, as long as things are
>    properly labled and credited. If you use some other operating
>    system with this mechanism, you need to discuss licensing terms
>    with us. If you want out of the GPL, you need to talk to us as
>    well.
>
>    If you violate or evade the terms of the GPL or our copyright,
>    you have invalidated this license to use the patented
>    mechanism. Our license applies only to the combination of RTLinux
>    with Linux, and we do not automatically license any other use of
>    the mechanism. We are very sympathetic to GPL uses of the patent
>    license. [top]

My reading of this is that the RTlinux code cannot be integrated into
some other GPLed OS, eg the Hurd, without incurring patent license
fees.  To my mind this should be enough to consign it to non-free.

It might be that the holders of the patent would permit its free use
in GPL-compatibly-licensed OSes other than Linux.  Perhaps someone
should ask them.