[oe] [PATCHv3 1/3] conf/layer.conf: Use .= for BBPATH and += for BBFILES

[Chris Larson]

On Mon, May 9, 2011 at 8:05 AM, Phil Blundell <philb at gnu.org> wrote:
> On Mon, 2011-05-09 at 07:48 -0700, raj.khem at gmail.com wrote:
>> From: Khem Raj <raj.khem at gmail.com>
>>
>> Provide additional commentary that should help a bit more
>
> I'm still struggling slightly to understand why this patch is an
> improvement.  As far as I can tell:
>
> - the change from prepending to appending BBPATH will alter all the
> priorities of the layers.  It isn't entirely obvious to me if (or why)
> this is a good thing; and
>
> - the change to the way that BBFILES is assigned doesn't make any
> functional difference.  Is that just a cosmetic change?
>
> Also:
>
>> +# It really depends on order of the layers appearing in BBLAYERS
>> +# variable in toplevel bblayers.conf file, where bitbake will search
>> +# for .inc files and others where bitbake uses BBPATH since it will
>> +# search the directories from first to last as specified in BBPATH
>> +# Therefore if you want a given layer to be considered high priority
>> +# for the .inc and .conf etc. then consider it adding at the beginning
>> +# of BBPATH. For bblayers bitbake will use BBFILES_PRIORITY to resolve
>> +# the recipe contention so the order of directories in BBFILES does
>> +# not matter.
>
> Maybe it's just my lack of familiarity with the code, but I find this
> comment rather difficult to parse.  Even after reading it a few times
> I'm not totally sure that I've grasped what the first sentence is
> saying.

The layer.conf files are parsed in the order of the layers in
BBLAYERS, and the resulting BBPATH will be based upon that and whether
the layer.conf files appended or prepended to it.  Recipe priority,
however, is governed by the BBFILE_ variables in the layer. So
responsibility over the priority of a given layer is split, in two
different places, the layer itself, and the user/project
configuration.
-- 
Christopher Larson
clarson at kergoth dot com
Founder - BitBake, OpenEmbedded, OpenZaurus
Maintainer - Tslib
Senior Software Engineer, Mentor Graphics