Re: [PULL v2 00/73] tcg plugins and testing updates

[Alex Bennée]

Markus Armbruster <address@hidden> writes:

> I hate to interfere with the merging of working code for non-technical
> reasons....
>
> This is a plugin interface.  As I wrote in reply to v4, I'd like to see
> a pragmatic argument why abuse of the plugin interface to circumvent the
> GPL is not practical.  This might include "not a stable interface", "you
> have to link with a truckload of gpl code", "the set of things you can
> do is deliberately extremely limited".

I included a link to the description in lead patch of the following two
revisions posted after v4 for this purpose. To repeat myself:

  QEMU TCG plugins provide a way for users to run experiments taking
  advantage of the total system control emulation can have over a guest.
  It provides a mechanism for plugins to subscribe to events during
  translation and execution and optionally callback into the plugin
  during these events. TCG plugins are unable to change the system state
  only monitor it passively. However they can do this down to an
  individual instruction granularity including potentially subscribing
  to all load and store operations.

So to summarise it is a deliberately limited set of passive observations
that can be made by the plugins. You cannot implement a new device using
this interface.

> Perhaps such an argument is made somewhere in these 73 patches already.
> I admit to not having read them all :)  In the TCG plugin design document
> perhaps?  Assuming it exists...

Indeed there is - docs/devel/plugins.rst

A high level tour of the design decisions and approaches is the subject
of my talk on Friday morning.

> I proposed discussing the project's requirements for external interfaces
> on GPL circumvention deterrence at the QEMU Summit next week.

That should certainly be an agenda item for the summit. I don't think
this provides a mechanism for GPL circumnavigation though.

> If merging this could be delayed until the licensing ramifications have
> become a bit more clear, I'd be obliged.

I'd rather not unless we can make an exception for late merging of the
PR. I've worked quite hard to make sure everything is ready for the 4.2
window and I'd rather not miss a whole release cycle on a
misunderstanding of what these plugins allow.

--
Alex Bennée