4.1.2.2. Kernel Modification Workflow

This illustration and the following list summarizes the kernel modification general workflow.

  1. Set up your host development system to support development using the Yocto Project: See "The Linux Distribution" and "The Packages" sections both in the Yocto Project Quick Start for requirements.

  2. Establish a local copy of project files on your system: Having the Source Directory on your system gives you access to the build process and tools you need. For information on how to get these files, see the bulleted item "Yocto Project Release" earlier in this manual.

  3. Establish the temporary kernel source files: Temporary kernel source files are kept in the Build Directory created by the OpenEmbedded build system when you run BitBake. If you have never built the kernel in which you are interested, you need to run an initial build to establish local kernel source files.

    If you are building an image for the first time, you need to get the build environment ready by sourcing an environment setup script (i.e. oe-init-build-env or oe-init-build-env-memres). You also need to be sure two key configuration files (local.conf and bblayers.conf) are configured appropriately.

    The entire process for building an image is overviewed in the "Building an Image" section of the Yocto Project Quick Start. You might want to reference this information. You can find more information on BitBake in the BitBake User Manual.

    The build process supports several types of images to satisfy different needs. See the "Images" chapter in the Yocto Project Reference Manual for information on supported images.

  4. Make changes to the kernel source code if applicable: Modifying the kernel does not always mean directly changing source files. However, if you have to do this, you make the changes to the files in the Build Directory.

  5. Make kernel configuration changes if applicable: If your situation calls for changing the kernel's configuration, you can use the yocto-kernel script or menuconfig to enable and disable kernel configurations. Using the script lets you interactively set up kernel configurations. Using menuconfig allows you to interactively develop and test the configuration changes you are making to the kernel. When saved, changes using menuconfig update the kernel's .config file. Try to resist the temptation of directly editing the .config file found in the Build Directory at tmp/sysroots/<machine-name>/kernel. Doing so, can produce unexpected results when the OpenEmbedded build system regenerates the configuration file.

    Once you are satisfied with the configuration changes made using menuconfig, you can directly compare the .config file against a saved original and gather those changes into a config fragment to be referenced from within the kernel's .bbappend file.

  6. Rebuild the kernel image with your changes: Rebuilding the kernel image applies your changes.