> -----Original Message-----
> From: [email protected] <openembedded-
> [email protected]> On Behalf Of Richard Purdie
> Sent: den 15 juni 2023 11:05
> To: Mikko Rapeli <[email protected]>
> Cc: Alexander Kanavin <[email protected]>;
> [email protected]; [email protected];
> Thomas Petazzoni <[email protected]>; Alexandre Belloni
> <[email protected]>
> Subject: Re: [OE-Core][PATCH v3 4/4] core-image-ptest: append ptest
> directory to artifacts list
>
> On Thu, 2023-06-15 at 11:34 +0300, Mikko Rapeli wrote:
> > Hi Richard,
> >
> > On Thu, Jun 15, 2023 at 08:03:44AM +0100, Richard Purdie wrote:
> > > On Sun, 2023-06-11 at 17:16 +0200, Alexander Kanavin wrote:
> > > > Doesn't += override the earlier ?=
> > >
> > > It depends. If ?= is parsed first, += will append. If the ?= is parsed
> > > after +=, the ?= will not happen as the variable has a value.
> > >
> > > > (or ??=),
> > >
> > > += would override ??=
> >
> > In which kind of cases would ??= be preferred?
> >
> > For basic recipes in oe-core and other layers, setting variables with
> > basic assignment and then appending it with += should be enough unless
> > machine
> > or other override specific qualifiers are needed :append:machine.
> >
> > Using plain :append without any qualifiers is annoying in downstream layers
> > which
> > try to fine tune upstream open source meta layers and recipes and still
> > remain compatible
> > to apply security and other updates, including full version/branch upgrades.
> >
> > I see some, for me, bad examples of ??= to set initial PACKAGECONFIG, for
> > example.
>
> This is all a big problem area and I've talked about it before. We
> can't make one recommendation which will work for every person in every
> scenario.
>
> The original intent was that ??= would be widely used and solve some of
> the problems. That plan was flawed but we (I?) didn't realise until too
> late.
>
> I'd not call ??= with PACKAGECONFIG as bad, it just doesn't do what you
> want in some scenarios.
>
> > Downstream layers would need to use PACKAGECONFIG:append to add some feature
> > to upstream defaults since += would require to fully control the
> > PACKAGECONFIG
> > in a bbappend. I would prefer ?= for that so that a += could be used to add
> > an
> > extra non-default feature but keep all the rest in upstream defaults.
> >
> > This gets even more tricky with intermediate layers which might want to
> > enable
> > features across recipes and layers, e.g. "selinux". Now they'd have to use
> > use :append
> > to make sure "selinux" is added to PACKAGECONFIG everywhere and no other
> > upstream defaults
> > are changed. And then product layers who 'know better' to for example drop
> > some features
> > would need to :remove them explicitly and can't fully overwrite the
> > PACKAGECONFIG with a simple
> > assignment in a bbappend. Messy. Staring a lot of "bitbake -e" ouput needed.
>
> I wish I had a magic answer. ?= has it's own set of issues too last
> time I sat and thought about all this :( I think the issues come if
> someone uses distro overrides from a config file instead of a bbappend.
>
> It needs time spending on it by someone willing to look at all the
> different use cases, including the ones they don't use themselves and
> come up with some kind of proposal. Personally, I'm willing but I can't
> even get through the patch review backlog or autobuilder intermittent
> bug queue at the moment :(.
>
> Cheers,
>
> Richard
I will not claim to know all use cases, but when it comes to
PACKAGECONFIG my belief is that using = is the right thing to do
in a recipe. The rationale is that the recipe is expected to be
the first instance to set it. Then any further modifications are
done via bbappends (or overrides, but the latter do not really
care whether =, ?= or ??= was used as they are applied after all
of them).
You can of course use ?= instead, but there really isn't a need
for it since any bbappend can just use = to override what the
recipe set using =, or use += to add to it.
Using ??= to set PACKAGECONFIG in the recipe on the other hand
is problematic as it means any bbappends must use :append to add
to it.
The most problematic aspect in this is when a bbappend wants to
remove a feature from the list, due to how :remove works. In a
perfect world, all bbappends would do something like this when
they need to use the :remove operator:
FOO = "foo"
PACKAGECONFIG:remove = "${FOO}"
That way there is at least a way to for a higher layer to restore
the feature.
Now things always get messy when you involve multiple layers
from different sources that all try to adapt the configuration
to their liking, so it is more than likely that my view is too
simplified. But I am convinced that both = and ?= are better
choices than ??= when setting PACKAGECONFIG in a recipe due to
how the latter one forces the use of :append in bbappends,
which the former two don't.
//Peter
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