Grout license feedback

[Robin Jarry]

Hi Morten,

Morten Brørup, Apr 14, 2026 at 10:54:
> Hi Robin & Maxime,
>
> Having followed Grout progress on the sideline, I was taking a look at
> it this morning, and the license struck me as unclear.
>
> As a fan of the BSD license, I have some feedback/questions.
>
> Please note: I'm not a license expert! Just happened to notice this,
> and wanted to provide my thoughts.
>
> The README says that the project is BSD licensed, and only the FRR
> plugin is GPL licensed.
>
> Doesn't the FRR plugin's GPL license "infect" the entire project? E.g.
> if someone forks Grout, contributes some code to the new project and
> distributes it as an executable, their project will be indirectly GPL
> licensed - e.g. they must provide the complete source code of their
> project - unless they remove the FRR plugin.
>
> Why the need to deviate from the BSD license?
>
> Assuming the FRR plugin is dynamically loadable, like a library, maybe
> LGPL would be a better license than GPL?

That is a good question. FRR/zebra plugins are dlopen()ed by zebra at
runtime. This makes dplane_grout.so automatically "infected" by the GPL
license.

NB: Including headers from a GPL license project does *not* propagate
the GPL license. The license is propagated only when code executes in
the same memory space as GPL licensed code (e.g. via dynamic linking or
dlopen).

However, dplane_grout.so is *not* linked against anything in grout. It
just uses symbols from grout public API headers. The communication
happens over a UNIX socket which does *not* propagate the GPL license.

So it is correct to have grout BSD licensed and the FRR plugin GPL
licensed.

> Another detail: The Contribution Guidelines
> [https://github.com/DPDK/grout/blob/1eb50571433d9a20378623012f4e0b750d160ec2/CONTRIBUTING.md]
> say:
>
> "All contributions are made under the BSD-3-Clause license."
>
> You should update this to mention that contributions to the FRR plugin
> are made under the GPL license. (Assuming you want to keep the plugin
> GPL licensed.)

Indeed this should be updated. The contribution guidelines were written
before we added the FRR plugin.

> PS: Looking forward to the next Grout presentations at the coming DPDK
> Summit. J

Thanks, I'll be there!

Cheers o/

Robin