[yocto] Good example of bbclass customization? maintainer

[Marcelo E. Magallon]

Hi,

I'm in the process of cleaning up our usage of Yocto with the goal of
improving longer-term maintainability, basically implementing something
like this:

http://events.linuxfoundation.org/sites/events/files/slides/Yocto-upgrades-ELC-2017.pdf

Right now I'm looking at several .bbclass files which have been
customized (meaning "someone edited the poky version directly"). My
general idea is that to support something like the above, I need to take
customizations to a different layer. In this way when poky-next's
foo.bbclass overlays poky's foo.bbclass, customizations aren't lost.

The simplest example of this that I have at hand is editting
image.bbclass to add:

	IMAGE_FEATURES[validitems] += "foo"
	FEATURE_PACKAGES_foo = "bar baz"

The practical effect of this modification can be accomplished in a
different way: I can have custom-image.bbclass "inherit image",
customize there and have my-image.bb "inherit custom-image" instead of
"inherit image". This works with the above, as custom-image.bbclass
would be customizing poky-next's image.bbclass, right?

My concern right now is a *different* case, where your goal is to modify
the class in order to affect all the recipes already inheriting from it.
For example, where there's a modification to a function in the class.

Is there a good example out there as to how to implement such a thing?

Thanks!

Marcelo