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Rework RTEMS licensing discussions.

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This now captures historical rationale along with cross-linking
code templates with license guidelines.

Closes #3962.
This commit is contained in:
Joel Sherrill 2020-04-30 16:29:06 -05:00
parent ccc473b69d
commit 2d22d7453d
2 changed files with 96 additions and 14 deletions
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19
eng/coding-conventions.rst
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@ -33,15 +33,16 @@ Source Documentation
Licenses
--------
* The RTEMS `License <https://devel.rtems.org/wiki/TBR/Website/License>`_. is the typical
and preferred license.
* 2- and 3-clause BSD, MIT, and other OSI-approved non-copyleft licenses
that permit statically linking with the code of different licenses
are acceptable.
* GPL licensed code is NOT acceptable, neither is LGPL.
See `this blog post explanation <http://gedare-csphd.blogspot.com/2013/05/software-licenses-with-rtems.html>`_.
for more information.
* Advertising obligations are NOT acceptable, but restrictions are permissible.
The RTEMS Project has strict requirements on the types of software licenses
that apply to software it includes and distributes. Submissions will be
summarily rejected that do not follow the correct license or file header
requirements.
* Refer to :ref:`LicensingRequirements` for a discussion of the acceptable
licenses and the rationale.
* Refer to :ref:`FileHeaderCopyright` for example copyright/license comment
blocks for various languages.
Language and Compiler
---------------------

91
eng/license-requirements.rst
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@ -9,8 +9,10 @@ Licensing Requirements
**********************
All artifacts shall adhere to RTEMS Project licensing
requirements. Currently, the preferred licenses are CC-BY-SA-4.0 license
for documentation and "Two Paragraph BSD" for source code.
requirements. Currently, the preferred licenses are:
* "Two Clause BSD" (BSD-2-Clause) for source code, and
* CC-BY-SA-4.0 license for documentation
Historically, RTEMS has been licensed under the GPL v2 with linking
exception (https://www.rtems.org/license). It is preferred that new
@ -19,7 +21,86 @@ previously submitted code to RTEMS under a historical license, please
grant the project permission to relicense. See
https://devel.rtems.org/ticket/3053 for details.
TBD - Convert the following to Rest and insert into this file
TBD - https://devel.rtems.org/wiki/Developer/Coding/Conventions#Licenses
For example templates for what to include in source code and
documentation, see :ref:`FileHeaderCopyright`.
TBD - Review and make sure this includes info on BSD variants
Rationale
---------
.. COMMENT: Thanks to Gedare Bloom for his 2013 blog which
.. COMMENT: discussed the rationale for RTEMS License section.
.. COMMENT: http://gedare-csphd.blogspot.com/2013/05/software-licenses-with-rtems.html
RTEMS is intended for use in real-time embedded systems in which the
application is statically linked with the operating system and all
support libraries. Given this use case, the RTEMS development team
evaluated a variety of licenses with with the goal of promoting use
while protecting both users and the developers.
Using the GNU General Public License Version 2 (GPLv2) unmodified
was considered but discarded because the GPL can only be linked statically
with other GPL code. Put simply, linking your application code statically
with GPL code would cause your code to become GPL code. This would force
both licensing and redistribution requirements onto RTEMS users. This
was completely unacceptable.
The GNU Lesser General Public License Version 2 (LGPLv2) was also
considered and deemed to not be a suitable license for RTEMS. This is
because it either requires use of a shared library that can be re-linked,
or release of the linked (application) code. This would require an
RTEMS-based embedded system to provide a "relinking kit." Again, this
license would force an unacceptable requirement on RTEMS users and deemed
unacceptable.
Newer versions of the GPL (i.e. version 3) are completely unsuitable
for embedded systems due to the additions which add further restrictions
on end user applications.
The historical RTEMS `License <https://www.rtems.org/license>`_ is a
modified version of the GPL version 2 that includes an exception to permit
including headers and linking against RTEMS object files statically. This
was based on the license used by GCC language runtime libraries at that
time. This license allows the static linking of RTEMS with applications
without forcing obligations and restrictions on users.
A problem for RTEMS is there are no copyleft licenses that are compatible
with the deployment model of RTEMS. Thus, RTEMS Project has to reject any
code that uses the GPL or LGPL, even though RTEMS has historically appeared
to use the GPL itself -- but with the exception for static linking, and also
because an upstream GPL version 2 project could at any time switch to
GPL version 3 and become totally unusable. In practice, RTEMS can only
accept original code contributed under the RTEMS License and code that
has a permissive license.
As stated above, the RTEMS Project has defined its preferred licenses.
These allow generation of documentation and software from specification
as well as allow end users to statically link with RTEMS and not incur
obligations.
In some cases, RTEMS includes software from third-party projects. In those
cases, the license is carefully evaluated to meet the project licensing
goals. The RTEMS Project can only include software under licenses which follow
these guidelines:
* 2- and 3-clause BSD, MIT, and other OSI-approved non-copyleft licenses
that permit statically linking with the code of different licenses
are acceptable.
* The historical RTEMS `License <https://www.rtems.org/license>`_ is
acceptable for software already in the tree. This software is being
relicensed to BSD-2-Clause, rewritten, or removed.
* GPL licensed code is NOT acceptable, neither is LGPL.
* Software which is dual-licensed in a manner which prevents free use
in commercial applications is not acceptable.
* Advertising obligations are not acceptable.
* Some license restrictions may be permissible. These will be considered
on a case-by-case basis.
In practice, these guidelines are not hard to follow. Critically,
they protect the freedom of the RTEMS source code and that of end users
to select the license and distribution terms they prefer for their
RTEMS-based application.