如何在 Yocto 中覆盖 a.conf 文件

Question

I know how to override a .bb file using a .bbappend one inside a custom layer, replicating the exact path of the original one.

But when the file to override is a .conf ? I'm reading the mega-manual but I cannot find this information (perhaps I'm looking at the wrong chapters).

UPDATE

This is an example of what I want to do. The original.conf file contains this line:

IMAGE_FEATURES[validitems] += "qtcreator-debug"

and I want to remove that. If it were a.bb file I would create a bbappend file with:

IMAGE_FEATURES[validitems] -= "qtcreator-debug"

Answer 1

Basically the.conf files are evaluated top-to-bottom. So you can always overwrite anything, and the exactly evaluation order is listed whenever you run bitbake -e on something, plus there is a verbose rundown of evalutaion on each variable too.

So, thats the one part. The other is, proper.conf files actually set their variables that are meant to be tuned with the ?= and ??= operators, which makes it easier to overwrite. So if the to-be-overwritten.conf is one that you are maintaining, consider rewriting it. If not, also think about why it maybe has not been written that way, and if overwriting it is actually the right solution or merely a duct tape solution.

Answer 2

There are multiple ways of doing this. 1) You can always override stuff in the local.conf, it has the highest evaluation priority. But the limitation is that the local.conf needs to be manually edited and changes are available only to the build with that specific local.conf. 2) If it makes sense, you can create a new conf file and inherit the original conf file using "require" and then override stuff. This is useful while creating new machine conf files based on the existing ones. 3) Finally, a brute force mechanism to override the complete conf file is to create a new conf file with the same name inside the custom layer, and setting the layer priority of the custom layer higher than the layer containing the original conf file. This means you'd have to maintain the overriding conf file yourself. This method is applicable for overriding bbclasses as well. 4) You can modify the IMAGE_FEATURES inside the image recipe as well (see http://cgit.openembedded.org/openembedded-core/tree/meta/recipes-sato/images/core-image-sato.bb ).