Yocto layer creation

Guide on creating your own custom yocto layer

Refferences:
yoctoproject
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Simple yocto layers follow this file structure:

⊢meta-layer     
 ͏  ͏ ⊢conf   
 ͏  ͏  ͏ ⊢layer.conf   
 ͏  ͏ ⊢recipes-layer  
 ͏  ͏  ͏ ͏  ⊢application    
 ͏  ͏  ͏  ͏  ͏ ͏   ͏⊢files    
 ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏  ͏⊢applicationbinary  
 ͏  ͏  ͏  ͏  ͏ ͏   ͏⊢application_0.1.bb 

Lets go folder by folder.

Main folder meta-layer can be called whatever and it will contain folders for recipes, layer config, and other misc files.

conf contains configs that define recipes of the layer and much more.

recipes-layer contains main recipe file folder and a .bb file which has all the instructions for bitbake to perform during recipe baking process.

recipes-layer/files is a folder that contains certain recipe files (application, scripts, configs, etc) that will be included during build process, keep in mind source code could also be included with compilation process during baking, but i wont go into detail here.

Config example

BBPATH .= ":${LAYERDIR}"
BBFILES += "${LAYERDIR}/recipes-*/*/*.bb \
            ${LAYERDIR}/recipes-*/*/*.bbappend"

BBFILE_COLLECTIONS += "meta-apps"
BBFILE_PATTERN_meta-apps = "^${LAYERDIR}/"
BBFILE_PRIORITY_meta-apps = "6"

LAYERSERIES_COMPAT_meta-apps = "scarthgap"

This is an example of a simple configuration file which defines main folder and recipe folders, collection name, priority, and version compatibility.
The recipe file from the layer with a higher priority number takes precedence. Priority values also affect the order in which multiple .bbappend files for the same recipe are applied.

Recipe example

SUMMARY = "NWT4 Qt Application"
LICENSE = "CLOSED"
SRC_URI = "file://NWT4 \
           file://nwt4.desktop \
           file://nwt4.sh"

S = "${WORKDIR}"

# Install files
do_install() {
    install -d ${D}${bindir}
    install -m 0755 ${WORKDIR}/NWT4 ${D}${bindir}/NWT4

    install -d ${D}${datadir}/applications
    install -m 0644 ${WORKDIR}/nwt4.desktop ${D}${datadir}/applications/nwt4.desktop

    install -d ${D}${datadir}/${PN}
    install -m 0755 ${WORKDIR}/nwt4.sh ${D}${datadir}/${PN}
}

# Ensure weston user can execute it
#FILES:${PN} += "${bindir}/NWT4 ${datadir}/applications/nwt4.desktop"

Simple recipe example that takes already compiled application and includes it in the final linux image.
do_install() function contains main instructions for bitbake to perform, in this example bitbake is taking the files from main “files” folder and relocating them in certain location in the image

For better understanding of directory and instalation variables check out koan wiki page