Bitbake append file to reconfigure kernel

Question

I'm trying to reconfigure some .config variables to generate a modified kernel with wifi support enabled. The native layer/recipe for the kernel is located in this directory:

    meta-layer/recipes-kernel/linux/linux-yocto_3.19.bb

First I reconfigure the native kernel to add wifi support (for example, adding CONFIG_WLAN=y):

    $ bitbake linux-yocto -c menuconfig

After that, I generate a "fragment.cfg" file:

    $ bitbake linux-yocto -c diffconfig

I have created this directory into my custom-layer:

    custom-layer/recipes-kernel/linux/linux-yocto/

I have copied the "fragment.cfg file into this directory:

    $ cp fragment.cfg custom-layer/recipes-kernel/linux/linux-yocto/

I have created an append file to customize the native kernel recipe:

    custom-layer/recipes-kernel/linux/linux-yocto_3.19.bbappend

This is the content of this append file:

    FILESEXTRAPATHS_prepend:="${THISDIR}/${PN}:"
    SRC_URI += "file://fragment.cfg"

After that I execute the kernel compilation:

    $ bitbake linux-yocto -c compile -f

After this command, "fragment.cfg" file can be found into this working directory:

    tmp/work/platform/linux-yocto/3.19-r0

However none of the expected variables is active on the .config file (for example, CONFIG_WLAN is not set).

How can I debug this issue? What is supposed I'm doing wrong?

Answer 1

When adding this configuration you want to use append in your statement such as:

SRC_URI_append = "file://fragment.cfg"

Answer 2

After analyzing different links and solutions proposed on different resources, I finally found the link https://community.freescale.com/thread/376369 pointing to a nasty but working patch, consisting in adding this function at the end of append file:

do_configure_append() {
    cat ${WORKDIR}/*.cfg >> ${B}/.config
}

It works, but I expected Yocto managing all this stuff. It would be nice to know what is wrong with the proposed solution. Thank you in advance!

Answer 3

If your recipe is based on kernel.bbclass then fragments will not work. You need to inherit kernel-yocto.bbclass

You can also use merge_config.sh scripts which is present in kernel sources. I did something like this:

do_configure_append () {
    ${S}/scripts/kconfig/merge_config.sh -m -O ${WORKDIR}/build ${WORKDIR}/build/.config ${WORKDIR}/*.cfg
}

Answer 4

Well, unfortunately, not a real answer... As I haven't been digging deep enough.

This was working alright for me on a Daisy-based build, however, when updating the build system to Jethro or Krogoth, I get the same issue as you.

Issue: When adding a fragment like

custom-layer/recipes-kernel/linux/linux-yocto/cdc-ether.cfg

The configure step of the linux-yocto build won't find it. However, if you move it to:

 custom-layer/recipes-kernel/linux/linux-yocto/${MACHINE}/cdc-ether.cfg

it'll work as expected. And it's a sligthly less hackish way of getting it to work.