Yocto Project integration

This section describes how to include a shared library or platform service in the target image using the Yocto Project. A key part of this is an open source build system, based around the OpenEmbedded architecture, that enables developers to create their own Linux distribution specific to their environment. BitBake is the build tool used in this setup:

BitBake executes tasks according to provided metadata that builds up the tasks. Metadata is stored in recipe (.bb) and related recipe “append” (.bbappend) files, configuration (.conf) and underlying include (.inc) files, and in class (.bbclass) files. The metadata provides BitBake with instructions on what tasks to run and the dependencies between those tasks.

The developed software components are added to the project through a BitBake recipe file that, as mentioned above, stores the component metadata. Guidelines on how to write BitBake recipes can be found in the Yocto reference manual and the reference structure is described in the OpenEmbedded style guide.

Template recipes

Below is a template Yocto recipe for the template-service. See inline comments for description of the different fields available.

# Various meta-data. Description is the only mandatory field here.
SUMMARY = "A template C/C++ service"
DESCRIPTION = "A C/C++ source code repository blueprint"
AUTHOR = "Gordan Markuš <gordan.markus@pelagicore.com>"
HOMEPAGE = "https://github.com/Pelagicore/template-service"

# Short license name and where to find the license file plus its checksum. This is so that yocto
# can check if the license text changes in newer versions of the software
LIC_FILES_CHKSUM = "file://LICENSE;md5=815ca599c9df247a0c7f619bab123dad"

# Dependencies for building this software.
DEPENDS = "template-library"

# Version and revision. It is in general possible to have several versions of the same software
# on the same system
PV = "1.0+git${SRCREV}"
PR = "r0"

# Where to find the sources and, in the case the source is at a cvs, what revision to build
SRCREV = "5bce3d20f996dac7e3882f48f5057abb7e1d05f5"
SRC_URI = "git://github.com/Pelagicore/template-service.git;protocol=https;branch=master"

# Where the sources are placed
S = "${WORKDIR}/git/"

# What classes to use. The template-service is a cmake project that uses pkgconfig. In general,
# just inheriting these classes makes building completely automatic without any need to tinker.
inherit cmake pkgconfig

Target image integration

To include the template service in the target image, the following line has to be added to the target image BitBake recipe:

IMAGE_INSTALL += "template-service"

Observe that there is no need to add the template library explicitly. The template library will be included implicitly because the template service depends on it.