possible consequences of adding "extraneous" layers to a build?

possible consequences of adding "extraneous" layers to a build?

[Robert P. J. Day]

  (currently updating a pile of my OE online pages so i'm going to ask
a bunch of basic questions to make sure i'm not missing anything.)

  what are the basic rules for layer design such that you should
(theoretically) be able to toss a bunch of ostensibly superfluous
layers into a build, and it shouldn't make a difference? that is,
leaving aside obvious conflicts in having two layers trying to define
precisely the same thing, what are the only issues you should worry
about in throwing more layers into your "bblayers.conf" file, even if
you end up not using anything from them?

  first, it seems(?) clear that introducing new recipes or classes or
machines or distros in those additional layers should make no
difference -- if you weren't referring to any of those features
before, then if you don't change your configuration, you certainly
won't be referring to them now.

  the most obvious consequence is that one or more .bbappend files
will tweak some recipes you were already building, so .bbappend files
strike me as, really, the only consequence of note.

  the only thing that leaps to mind is if some really weird content
was placed in the new layers' "layer.conf" file, but that strikes me
as really bad design unless there's a good reason for it.

  so ... is there any other possible consequence of adding layers to a
build that i'm overlooking?

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

Re: possible consequences of adding "extraneous" layers to a build?

[Richard Purdie]

On Sat, 2017-02-18 at 13:25 -0500, Robert P. J. Day wrote:
>   (currently updating a pile of my OE online pages so i'm going to
> ask
> a bunch of basic questions to make sure i'm not missing anything.)
> 
>   what are the basic rules for layer design such that you should
> (theoretically) be able to toss a bunch of ostensibly superfluous
> layers into a build, and it shouldn't make a difference? that is,
> leaving aside obvious conflicts in having two layers trying to define
> precisely the same thing, what are the only issues you should worry
> about in throwing more layers into your "bblayers.conf" file, even if
> you end up not using anything from them?
> 
>   first, it seems(?) clear that introducing new recipes or classes or
> machines or distros in those additional layers should make no
> difference -- if you weren't referring to any of those features
> before, then if you don't change your configuration, you certainly
> won't be referring to them now.
> 
>   the most obvious consequence is that one or more .bbappend files
> will tweak some recipes you were already building, so .bbappend files
> strike me as, really, the only consequence of note.
> 
>   the only thing that leaps to mind is if some really weird content
> was placed in the new layers' "layer.conf" file, but that strikes me
> as really bad design unless there's a good reason for it.
> 
>   so ... is there any other possible consequence of adding layers to
> a
> build that i'm overlooking?

A layer can do pretty much *anything* to the build. You can design
layers not to have an impact, or the impact may be the whole purpose of
the layer.

With YP Compatible v2, we plan to detect "invasive" changes using the
sstate checksums changing to show that the layer did something
unexpected. But in general a layer can do pretty much anything.

Cheers,

Richard

Re: possible consequences of adding "extraneous" layers to a build?

[Robert P. J. Day]

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On Sun, 19 Feb 2017, Richard Purdie wrote:

> On Sat, 2017-02-18 at 13:25 -0500, Robert P. J. Day wrote:
> >   (currently updating a pile of my OE online pages so i'm going to
> > ask a bunch of basic questions to make sure i'm not missing
> > anything.)
> >
> >   what are the basic rules for layer design such that you should
> > (theoretically) be able to toss a bunch of ostensibly superfluous
> > layers into a build, and it shouldn't make a difference? that is,
> > leaving aside obvious conflicts in having two layers trying to
> > define precisely the same thing, what are the only issues you
> > should worry about in throwing more layers into your
> > "bblayers.conf" file, even if you end up not using anything from
> > them?
> >
> >   first, it seems(?) clear that introducing new recipes or classes
> > or machines or distros in those additional layers should make no
> > difference -- if you weren't referring to any of those features
> > before, then if you don't change your configuration, you certainly
> > won't be referring to them now.
> >
> >   the most obvious consequence is that one or more .bbappend files
> > will tweak some recipes you were already building, so .bbappend
> > files strike me as, really, the only consequence of note.
> >
> >   the only thing that leaps to mind is if some really weird
> > content was placed in the new layers' "layer.conf" file, but that
> > strikes me as really bad design unless there's a good reason for
> > it.
> >
> >   so ... is there any other possible consequence of adding layers
> > to a build that i'm overlooking?
>
> A layer can do pretty much *anything* to the build. You can design
> layers not to have an impact, or the impact may be the whole purpose
> of the layer.
>
> With YP Compatible v2, we plan to detect "invasive" changes using
> the sstate checksums changing to show that the layer did something
> unexpected. But in general a layer can do pretty much anything.

  i understand that a layer can do pretty much *anything*, what i was
more interested in is what it *shouldn't* do unless it comes with huge
warning signs telling you about it. as a more concrete example, if
someone says, "hey, i have this great new layer that provides all
sorts of cool recipes," i'd want to to know that i can add it to
bblayers.conf and, unless i explicitly choose to start using content
from it, it shouldn't quietly change my current build.

rday

-- 

========================================================================
Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
LinkedIn:                               http://ca.linkedin.com/in/rpjday
========================================================================

Re: possible consequences of adding "extraneous" layers to a build?

[Andre McCurdy]

On Sun, Feb 19, 2017 at 10:19 AM, Robert P. J. Day
<rpjday@crashcourse.ca> wrote:
> i understand that a layer can do pretty much *anything*, what i was
> more interested in is what it *shouldn't* do unless it comes with huge
> warning signs telling you about it. as a more concrete example, if
> someone says, "hey, i have this great new layer that provides all
> sorts of cool recipes," i'd want to to know that i can add it to
> bblayers.conf and, unless i explicitly choose to start using content
> from it, it shouldn't quietly change my current build.

The priority of recipes within the layers (ie BBFILE_PRIORITY_xxx)
gives a good indication of that. Layers which just provide cool news
recipes (ie fill in gaps in oe-core) generally have a priority lower
than or equal to oe-core. BSP or distro layers (which often need to
over-ride or modify stuff in oe-core) generally have a priority higher
than oe-core. You should be very cautious about adding new distro or
BSP layers to your build.

> rday
>
> --
>
> ========================================================================
> Robert P. J. Day                                 Ottawa, Ontario, CANADA
>                         http://crashcourse.ca
>
> Twitter:                                       http://twitter.com/rpjday
> LinkedIn:                               http://ca.linkedin.com/in/rpjday
> ========================================================================