"In response to worries about the possibility of
patent-infringement lawsuits arising from the granting of a patent
covering certain techniques used in RTLinux, the open source
license covering portions of RTAI (a competing real-time extension
to Linux) has recently been changed from LGPL to GPL. The change in
license status of certain of RTAI's components was quietly phased
in as part of the RTAI-24.1.8 release.
"Based on the change in license, the RTAI team now believes that
the new partly-GPL RTAI is covered by the terms of Version 2 of the
Open RTLinux Patent License , which says: 'The Patented Process may
be used, without any payment of a royalty, with two types of
software.' Specifically, the partly-GPL version of RTAI would
appear to fall within the first type described in the patent
license. A statement from Free Software Foundation counsel Eben
Moglen apparently supports that position.
"However, while the change in the license status of portions of
RTAI hopefully eliminates the possibility that all RTAI users might
be required to purchase a license to use the RTLinux patent, it
introduces a new concern, based on what is sometimes referred to as
the "viral effect" of GPL. Namely: Does the change in license of
portions of RTAI, from LGPL to GPL, require that the source code of
proprietary applications based on RTAI be made available to those
who request it?..."