[OE-core] Changing external kernel module results in rebuild of whole kernel

[Richard Purdie]

On Wed, 2015-05-06 at 08:35 +0200, Mike Looijmans wrote:
> Something in recent OE-core triggered a weird dependency "backfire".
> 
> If I change a recipe for a kernel module (a bb recipe that does "inherit 
> module") this will trigger a rebuild of the whole kernel.
> 
> This turns the 5-second job of just updating a single module into a several 
> minute workout for the build machine, and then causes boards to re-write the 
> kernel into flash needlessly when upgrading.
> 
> I now see this on all projects using OE-core master. I can't really pin what 
> caused it though. Anyone else seen this?

I have a suspicion this may be as a result of the changed kernel build
process in 1.8. 

The idea there is that the modules depend on the kernel source and
rather than taring up and then extracting a large (GB) sized sstate
object, we just extract the original kernel source.

So is the kernel really rebuilding, or, is it just extracting source for
the kernel to build against? I noticed rm_work in your other post and
this may also be some bad interaction between rm_work and the kernel
build process changes.

Cheers,

Richard