Menuconfig or how to configure kernel

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1 Linux configuration genericity[edit]

The process of building a kernel has two parts: configuring the kernel options and building the source with those options.

The Linux® kernel configuration is found in the generated file: .config.

.config is the result of configuring task which is processing platform defconfig and fragment files if any.


For OpenSTLinux distribution the defconfig is located into the kernel source code and fragments into stm32mp BSP layer :

- arch/arm/configs/multi_v7_defconfig

Every new kernel version brings a bunch of new options, we do not want to back port them into a specific defconfig file each time the kernel releases, so we are using the same defconfig file based on ARM SoC v7 architecture.
STM32MP1 specificities are managed with fragments config files.

- meta-st/meta-st-stm32mp/recipes-kernel/linux/linux-stm32mp/<kernel version>/fragment-*.config

.config result is located in the build folder:

- build-openstlinuxweston-stm32mp1/tmp-glibc/work/stm32mp1-openstlinux_weston-linux-gnueabi/linux-stm32mp/4.14-48/linux-stm32mp1-standard-build/.config

To modify the kernel options, it is not recommended to edit this file directly.

  • A user runs either a text-mode :
   PC $> make config 
starts a character based question and answer session (Figure 1)
Figure 1. Configuring the kernel with make config


   PC $> make menuconfig 
starts a terminal-oriented configuration tool (using ncurses) (Figure 2)
The ncurses text version is more popular and is run with the make menuconfig option.
Wikipedia Menuconfig[1] also explains how to "navigate" within the configuration menu, and highlights main key strokes. 
Figure 2. Make menuconfig makes it easier to back up and correct mistakes


  • or a graphical kernel configurator :
   PC $> make xconfig 
starts a X based configuration tool (Figure 3)
Figure 3. The Qt-Based make xconfig


Ultimately these configuration tools edit the .config file.

An option indicates either some driver is built into the kernel ("=y") or will be built as a module ("=m") or is not selected.

The unselected state can either be indicated by a line starting with "#" (e.g. "# CONFIG_SCSI is not set") or by the absence of the relevant line from the .config file.


The 3 states of the main selection option for the SCSI subsystem (which actually selects the SCSI mid level driver) follow. Only one of these should appear in an actual .config file:

CONFIG_SCSI=y
CONFIG_SCSI=m
# CONFIG_SCSI is not set

2 Menuconfig and Developer Package[edit]

For this use case, the prerequesite is that OpenSTLinux SDK has been installed and configured.

To verify if your cross-compilation environment has been put in place correctly, run the following command:

PC $> set | grep CROSS
CROSS_COMPILE=arm-openstlinux_weston-linux-gnueabi-

For more details, refer to <Linux kernel installation directory>/README.HOW_TO.txt helper file (the latest version of this helper file is also available in this user guide: README.HOW_TO.txt).

  • Go to the <Linux kernel build directory>
PC $> cd <Linux kernel build directory>
  • Save initial configuration (to identify later configuration updates)
PC $> make arch=ARM savedefconfig 
Result is stored in defconfig file
PC $> cp defconfig defconfig.old
  • Start the Linux kernel configuration menu
PC $> make arch=ARM menuconfig
  • Navigate forwards or backwards directly between feature
    • un/select, modify feature(s) you want
    • When the configuration is OK : exit and save the new configuration
usefull keys to know:
enter: enter in config subdirectory
space: hit several times to either select [*], select in module [m] or unselect [ ] 
/: to search for a keyword, this is usefull to navigate in tree
?: to have more information on selected line
  • Compare the old and new config files after operating modifications with menuconfig
PC $> make arch=ARM savedefconfig

Retrieve configuration updates by comparing the new defconfig and the old one

PC $> meld defconfig defconfig.old
  • Cross-compile the Linux kernel (please check the load address in the README.HOW_TO.txt helper file)
PC $> make arch=ARM uImage LOADADDR=<loadaddr of kernel>
PC $> cp arch/arm/boot/uImage install_artifact/boot/
  • Update the Linux kernel image on board
PC $> scp install_artifact/boot/uImage root@<board ip address>:/boot/
Info.png If the /boot mounting point doesn't exist yet, please see how to create a mounting point
  • Reboot the board
Board $> cd /boot; sync; systemctl reboot

Note that this use case modifies the configuration file in the Linux kernel build directory, not in the Linux kernel source directory: this is a temporary modification useful for a prototyping.

  • To make this temporary modification permanent, the delta between defconfig and defconfig.old must be saved in a configuration fragment file (fragment-*.config) based on fragment.cfg file, and the Linux kernel configuration/compilation steps must be re-executed (as explained in the README.HOW_TO.txt helper file).

3 Menuconfig and Distribution Package[edit]

  • Start the Linux kernel configuration menu
PC $> bitbake virtual/kernel -c menuconfig
  • Navigate forwards or backwards directly between feature
    • un/select, modify feature(s) you want
    • When the configuration is OK : exit and save the new configuration
usefull keys to know:
enter: enter in config subdirectory
space: hit several times to either select [*], select in module [m] or unselect [ ] 
/: to search for a keyword, this is usefull to navigate in tree
?: to have more information on selected line
  • Compare the old and new config files after operating modifications with menuconfig
PC $> bitbake -c diffconfig  
Config fragment has been dumped into:
.../build-openstlinuxweston-stm32mp1/tmp-glibc/work/stm32mp1-openstlinux_weston-linux-gnueabi/linux-stm32mp/4.14-48/fragment.cfg

Comparison result is stored in the fragment.cfg file

  • Cross-compile the Linux kernel
PC $> bitbake virtual/kernel
  • Update the Linux kernel image on board
PC $> scp <build dir>/tmp-glibc/deploy/images/<machine name>/uImage root@<board ip address>:/boot
Info.png If the /boot mounting point does not exist yet, please see how to create a mounting point
  • Reboot the board
Board $> cd /boot; sync; systemctl reboot

Note that this use case modifies the configuration file in the Linux kernel build directory, not in the Linux kernel source directory: this is a temporary modification useful for a prototyping.

  • To make this temporary modification permanent, it must be saved in a configuration fragment file (fragment-*.config) based on fragment.cfg file, and the Linux kernel configuration/compilation steps must be re-executed: bitbake <name of kernel recipe>.

4 References[edit]

Board support package

Software development kit

Attachments

Discussions