How to add a customer application

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1. Article purpose

The main purpose of this article is to give main steps on how to add a customer application or an already existing application inside the Yocto build process (with the Distribution Package).

2. Pre-requesite

You are already familiar with the Yocto build process and the OpenSTLinux distribution.

You have already created a customer layer (How to create a new open embedded layer) or want to add an already existing application to update, for your own needs, the OpenSTLinux distribution.

You have already created in your environment either an external out of tree kernel module, or an "hello world" user space example.

3. Adding an application

3.1. Adding an application already present in layers

You may want to add an application which is already present in layers, for example OpenCV. You can search for it.

 bitbake -s|grep opencv

If nothing is displayed, it can be because this recipe is not included in your layers. You can try to search for it.

  find . -type f -iname "opencv*.bb"
 ./layers/meta-openembedded/meta-oe/recipes-support/opencv/opencv_3.4.3.bb

If the find command displays a recipe, then add the layer to your configuration

To check that this application can be built, compile it with the bitbake command:

 bitbake opencv

You can now add it to an image.

3.2. Adding a customer application (integrated in a customer layer)

Once mymodule or myhelloworld recipes have been created with devtool commands, to add it in the Yocto build process, some additional commands below must be used.
They concern the external out-of-tree Linux kernel module (mymodule).
Similar commands shall be executed for the "hello world" user space example (myhelloworld).

Copy the new recipe inside the customer layer

 mkdir ../meta-my-custo-layer/recipes-custom/mymodule
 cp workspace/recipes/mymodule/mymodule.bb ../meta-my-custo-layer/recipes-custom/mymodule

Copy the source code files, the Makefile inside the customer layer

 mkdir ../meta-my-custo-layer/recipes-custom/mymodule/mymodule
 cp kernel_module_example/Makefile ../meta-my-custo-layer/recipes-custom/mymodule/mymodule
 cp kernel_module_example/kernel_module_example.c ../meta-my-custo-layer/recipes-custom/mymodule/mymodule
 devtool reset mymodule

Some fields of new recipes must be also completed, at least LICENSE, LIC_FILES_CHKSUM, and SRC_URI

Details on the license are explained in Yocto Megamanual New Recipe Licensing
Details on SRC_URI are explained in Yocto Megamanual New Recipe fetching code

Warning

The recipe update must be done now directly in ../meta-my-custo-layer/recipes-custom/mymodule/mymodule.bb

# NOTE: LICENSE is set to "CLOSED" to allow you to at least start building - if
# this is not accurate with respect to the licensing of the software being built (in most cases, it
# is not) you must specify the correct value, before using this
# recipe for anything other than the initial testing/development!
LICENSE = "CLOSED"
LIC_FILES_CHKSUM = ""

# No information for SRC_URI yet (only an external source tree is specified)
SRC_URI = ""

For instance for Linux kernel module:

LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.GPLv2;md5=751419260aa954499f7abaabaa882bbe"

SRC_URI = "file://Makefile \
           file://kernel_module_example.c \
          "

Or for user space application:

LICENSE = "MIT"
LIC_FILES_CHKSUM = "file://${COREBASE}/meta/COPYING.MIT;md5=3da9cfbcb788c80a0384361b4de20420"

SRC_URI = "file://hello_world_example.c \
          "

To check that your updates of new recipe have not broken the compilation, compile it with the bitbake command:

 bitbake mymodule

You can now add it to an image.

4. Quickly add the recipe to an image

For a quick check you can add this new recipe (mymodule.bb) inside st-image-weston, recompile this image, flash/boot the board and check the module is well functionnal

 cd .../meta-st-openstlinux/recipes-st/images/

Open st-image-weston.bb and add this line : CORE_IMAGE_EXTRA_INSTALL += " mymodule "

 bitbake st-image-weston

After flashing and booting the board, Insert the kernel module example into the Linux kernel

 modprobe kernel_module_example
[18167.821725] Kernel module example: hello world from STMicroelectronics

Remove the kernel module example from the Linux kernel

 rmmod kernel_module_example
[18180.086722] Kernel module example: goodbye from STMicroelectronics

Once this quick check is done, please remove the addon in st-image-weston

Create your custom image by following the recommendation made in How to create your own image (chapter 4.2.3).
This new recipe (mymodule.bb) must be added inside the custom image you compile

 cd .../meta-my-custo-layer/recipes-samples/images/

Open my-custom-image.bb and add this line : IMAGE_INSTALL += "mymodule"

 bitbake <my custome image>