====== Tips ======

  * [[https://stackoverflow.com/questions/51002891/overwriting-yocto-classes-through-meta-layer|Overwriting Yocto Classes through meta-layer]]

===== manual patching =====

According to ''src/poky/meta/classes-recipe/kernel-yocto.bbclass'' kernel patches are skipped if 'patchdir' exists.
``kernel-yocto.bbclass`` cannot handle this special case so patches needs to be applied manually.

<code bash>
OVERLAY_PREFIX="${SOURCE_PREFIX}/linux_5_15/overlay"
SRC_URI:append = " \
        file://0003-xxx.patch;patchdir=${OVERLAY_PREFIX};subdir=${OVERLAY_PREFIX} \
        file://0004-xxx.patch;patchdir=${OVERLAY_PREFIX};subdir=${OVERLAY_PREFIX} \
"

do_patch:prepend() {
    patch -b -d ${OVERLAY_PREFIX} -p 1 -i 0003-xxx.patch
    patch -b -d ${OVERLAY_PREFIX} -p 1 -i 0004-xxx.patch
}
</code>

It is possible to use generic Yocto patcher and call <code python>bb.build.exec_func('patch_do_patch', d)</code>
as it is performed by recipes: 
  * ''src/meta-openembedded/meta-oe/recipes-multimedia/id3lib/id3lib_3.8.3.bb''
  * ''src/meta-openembedded/meta-networking/recipes-support/netcat/netcat-openbsd_1.195.bb''

===== black list recipe =====

  * create bbappend and set ''COMPATIBLE_MACHINE = "x"'' to prevent use of recipe
  * BBMASK
    * <code bash>BBMASK += "meta-rity/meta/recipes-core/init-ifupdown/init-ifupdown_%.bbappend"</code>

===== Pass env variables to bitbake =====

To control additional or user defined recipe's variables from env (usefull for CI) add variables to ''BB_ENV_PASSTHROUGH_ADDITIONS'':
<code bash>
export foo="BAR"
export BB_ENV_PASSTHROUGH_ADDITIONS="${BB_ENV_PASSTHROUGH_ADDITIONS} foo BUILD_VERSION CI_COMMIT_BRANCH CI_COMMIT_SHORT_SHA"
bitbake ...
</code>




===== add files to rootfs =====

''IMAGE_PREPROCESS_COMMAND += "rsync -a --exclude=.git ${FILE_SRC}/rootfs/* ${WORKDIR}/rootfs;"''

===== override .conf =====

No override or appends mechanism. But some workaround possible:

  - override variables in ''local.conf''
  - create new conf file and inherit old one with ''require''
  - create new conf file with the same name to mask old file (take care of layer priority)

===== MACHINEOVERRIDES =====

When creatung new machine.conf based on existing one [[https://docs.yoctoproject.org/ref-manual/variables.html?highlight=machineoverrides#term-MACHINEOVERRIDES|MACHINEOVERRIDES]] can be used:

[[https://github.com/Freescale/meta-freescale/blob/master/classes/machine-overrides-extender.bbclass|machine-overrides-extender.bbclass]]

===== logging =====

<code bash>
inherit logging

bb.debug("HELLO = %s" % HELLO)

</code>