[Openembedded-architecture] LICENSE and LICENSE_pkg

[Markus Lehtonen]

There seems to be confusion and uncertainty (me included) regarding the
usage of LICENSE and LICENSE_pkg variables - see discussion in [1] and
[2]. The variables are not well documented and they are used somewhat
incoherently even inside oe-core.

The current (unwritten) guideline is that LICENSE is a source-level
value, a union containing all the (possible) licenses in the package.
It is also the default license used for all binary subpackages, but,
LICENSE_pkg values can be used to refine the license on subpackage
level. LICENSE_pkg should never contain anything that isn't also
specified in LICENSE.

However, there are recipes that currently use it incorrectly – at least
hdparm in oe-core (see [3]). It uses LICENSE as just a default binary
license (without including all LICENSE_pkg values) and LICENSE_pkg for
one differently licensed subpackage. We could fix all the recipes like
this, of course, but it is not necessarily the best solution.

The basic problem is probably best illustrated by the question "how do
I package 'mypkg' where one binary subpackage needs to be GPLv2 but all
other 20 binary packages are BSD?"

Currently, you'd need to define something like:
LICENSE = "BSD & GPLv2"
LICENSE_mypkg = "BSD"
LICENSE_mypkg-dev = "BSD"
LICENSE_mypkg-dbg = "BSD"
LICENSE_mypkg-subpkg1 = "BSD"
...
LICENSE_mypkg-subpkgX = "BSD"
LICENSE_mypkg-subpkgZ = "GPLv2"


This is not very maintainer-friendly and I think that this should be
improved. Some possible solutions that I can think of are:

1. Add a new LICENSE_DEFAULT variable that would define the default
binary license. The variable would be optional and default to LICENSE.
In the case of the example above, you would define:
LICENSE = "BSD & GPLv2"
LICENSE_DEFAULT = "BSD"
LICENSE_mypkg-subpkgZ = "GPLv2"

2. Change interpretation of LICENSE so that it would be the default
binary license. Wherever source-level license is needed, it would be
constructed as a union of LICENSE and all LICENSE_pkg values. The
source-level license could be provided by an optional LICENSE_ALL
variable (or similar) that would default to LICENSE. In our example you
would simply define:
LICENSE = "BSD"
LICENSE_mypkg-subpkgZ = "GPLv2"

>From these, I'd prefer #1 as it does not alter (and/or break) anything
that we currently have. It should be relatively easy to implement with
only minor changes to package* bbclasses. I also like the current idea
that LICENSE is a source-level union of all license. Option #2 would
change the interpretation of LICENSE and would require more invasive
changes, and, auditing all code involving LICENSE. When done properly,
it shouldn't break anything we currently have. However, automatically
making a union of the licenses has its pitfalls as the license
definitions can be complex logical expressions. Neither is perfect,
comments and better suggestions are welcome.


Thanks,
  Markus



[1] http://lists.openembedded.org/pipermail/openembedded-core/2016-May/
122161.html
[2] https://bugzilla.yoctoproject.org/show_bug.cgi?id=9499
[3] http://git.openembedded.org/openembedded-core/tree/meta/recipes-ext
ended/hdparm/hdparm_9.48.bb?id=c4dda05cb9755cb865c1d1bd142196f8a9f45d3d