[yocto] under what circumstances is BBCLASSEXTEND = "native" required in a recipe?

[Chris Larson]

On Sat, Aug 11, 2012 at 11:32 AM, Robert P. J. Day
<rpjday at crashcourse.ca> wrote:
> On Sat, 11 Aug 2012, Chris Larson wrote:
>
>> On Sat, Aug 11, 2012 at 10:03 AM, Robert P. J. Day
>> <rpjday at crashcourse.ca> wrote:
>> >   however, the "chrpath" command is not listed in bitbake as part of
>> > ASSUME_PROVIDED, and its recipe includes the line
>> >
>> >   BBCLASSEXTEND = "native"
>> >
>> > that's what's confusing -- if the QS guide demands that the user
>> > install "chrpath" manually, what is the subsequent value of its recipe
>> > dictating that it be natively buildable?
>>
>> At a guess, it's possible that not all recipes that needed
>> chrpath-native had an explicit dependency on it, or similar. Your
>> question is specific to chrpath, not at all general to
>> BBCLASSEXTEND. Adding native to bbclassextend means that a -native
>> version of the recipe can be built. The question of why certain
>> things are expected on the host vs built from that recipe is an
>> entirely different one.
>
>   i believe i see your logic.  just to clarify, it seems somewhat
> redundant to a) *require* the developer to manually install certain
> commands on the yocto dev host, and b) simultaneously have a recipe
> for that command that allows it to be built natively, in case yocto
> needs it.
>
>   does that make sense?  i'm assuming the sole reason to support a
> -native build in a recipe is for yocto use on the dev host, right?
>
> rday
>
> p.s.  as a more obvious example, consider "git".  it's now
> "ASSUME_PROVIDED", and listed in the quick start guide as required on
> the dev host, but it also still supports a native build.  i'm just
> trying to clarify that, in cases like that, supporting the -native
> build is no longer necessary.  or am i missing something?

Supporting it isn't necessary, this is true, but we do want to remove
as many hard host dependencies as possible over time, no? Perhaps the
bbclassextend only exists to prepare for such a point. Also, having a
-native available doesn't *harm* anything. At most it slightly
increases ram usage up front when it produces the second variation of
the recipe.
-- 
Christopher Larson