[yocto] creating global variables in a recipes

[Richard Purdie]

On Wed, 2012-02-01 at 11:50 -0500, William Mills wrote:
> I am not sure I can give you a better option that local.conf but I can 
> explain why what your doing does not work.
> 
> It may feel from your usage that the image recipe is the ancestor of all 
> the recipes but this is really not true.  The settings in a image recipe 
> effect the assembly of that image and not the packages that they depend 
> on.  An image could be assembled from packages that were built long ago 
> or inherited via shared state.
> 
> settings in local,conf on the other hand affect all recipes.  If you add 
> something there it will be seen by all recipes.  Unfortunately this 
> means that all recipes are dependent on the settings and everything will 
> need to be rebuilt in case the new setting effects them.  I believe this 
> also means you will not be able to used share state with someone with a 
> different setting of (or unset) SOME_VARIABLE.  (Well you can but you 
> will both be rebuild everything.)

Just a small clarification:

With sstate, it actually depends whether SOME_VARIABLE is used by the
given sstate task or its dependencies. We have variable dependency
tracking code and can tell where variables are used and with what value.

The end result is you can have different local.conf files and share
sstate output in many cases, but real differences to the individual task
inputs will get accounted for.

Cheers

Richard