Layer licensing and charm licensing

[Mark Shuttleworth]

Hi folks

The move to layers, which is fantastic from a charming productivity
point of view, will also raise the question of licensing in a
cross-charm way. Originally, we envisaged each charm being licensed by
the charmer independently, but layers introduce cross-cutting licensing
questions, and in particular, questions about copyleft.

It certainly is not our intent that contributions from Canonical (which
we generally prefer to make under copyleft licenses) should force a
charm author to pick a copyleft license for their own contributions to
their own charm.

There are two options for common code that would be obvious solutions -
a limited copyleft (LGPL) and a permissive (Apache2 or BSD). Both
options enable people to bring shared public layers into their charms
but still pick their own licenses for their own layers and additional
bits. The LGPL option would require people modifying shared layers to
allow others to use their modifications ("if you edit this file, we can
merge your edits") but any new pieces created by them (typically
specific to their charms) could be restricted for their own use.

The OSM project, which is using charms for telco application modelling,
has a preference for Apache2, which is arguably also a preference for
many other industrial-scale initiatives.

We could also dual-license these components (Apache2 + LGPL, or even
Apache2 + GPL).

Am writing to gather feedback from the charmer community as to your
preferences in this regard.

Mark
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