[yocto-ab] Yocto Project Compatible v2

[Richard Purdie]

Since I seem to be making a few proposals, I think it also makes sense
for me to summarise what I believe we need to do with Yocto Project
Compatible.

I believe if we're improving the website, the time is right for a v2
programme. The biggest change I want to make is the one I've talked
about for a while. This is where we use the sstate signatures to make
automated tests of layers for compatibility. In principle this is
straight forward. A machine layer (containing conf/machine/*.conf
files) should be able to be added to bblayers.conf without changing the
sstate checksums of target recipes. The only time the checksums would
change is if the MACHINE is set to select the specific machine.
Similarly, a distro layer would only change checksums if and only if
DISTRO is actually selected. No layer would contain both distro files
and machine files. We already have examples of these kinds of sstate
tests in oe-selftest.

The compatibility questions would then have an additional one stating
that they could run some script without errors.

The only other major change I'd like to consider is mandating some kind
of "this layer is compatible with versions X, Y" markup in the layer.
The system could then use this to warn a user when they try and use a
layer designed for fido with krogoth etc. This is mainly a technical
question of deciding how best to do this (likely in layer.conf), then
we just require it for YP compatible.

In addition, I'd like to write a Q&A guidance document to go alongside
the questions which would be based on the things that have been asked
since the original programme launched. It would clarify some of the
common questions and issues people run into.

With an improved website and some advocacy around this, I believe we
could show better value to the project and also at the same time deal
with some of the compatibility issues people face.

Again, this is really a straw man proposal but should give us a
starting point to discuss. My main struggle with this has been finding
time to write the script and/or the QA document but I don't believe
these should be too difficult, I just need to prioritise it.

Thoughts/comments/feedback welcome!

Cheers,

Richard