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buildroot

Buildroot - extract a custom board/buildroot config/kernel config out of tree

I have customized buildroot with the new board ( derived from raspberry pi zero ). So my changes are (in-tree):

.config
board/passkeeper/genimage-passkeeper.cfg
board/passkeeper/post-build.sh
board/passkeeper/post-image.sh
board/passkeeper/rootfs_overlay/etc/init.d/S41passkeeper
board/passkeeper/rootfs_overlay/etc/mdev.conf
board/passkeeper/rootfs_overlay/etc/udhcpd.conf
configs/passkeeper_defconfig
output/build/linux-custom/.config

Now, reading the documentation - I am a bit confused on how to put all these things into the separate folder via BR2_EXTERNAL. Also I'm not sure how do I move the linux configuration from output/build/linux-custom/.config

make linux-update-defconfig BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE=/tmp/passkeeper/linux/linux-config

results in 

Unable to perform linux-update-defconfig when using a defconfig rule

Can somebody please provide step-by-step guide on that?

Solution

  • [You are asking two questions. I will answer only the question about saving the linux .config file; the other question is too generic.]

    You need to set the appropriate options in menuconfig, not just override on the command line, otherwise they are inconsistent.

    The process complete for creating a linux defconfig based on a pre-existing in-tree defconfig is the following. You have already done steps 1, 2 and 3.

    1. In the Buildroot configuration, select BR2_LINUX_KERNEL_USE_DEFCONFIG or BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG.
    2. Run make linux-menuconfig and adapt the linux configuration to your needs.
    3. Build and test, iterate over 2 until you have the configuration you want.
    4. In the Buildroot configuration, switch to BR2_LINUX_KERNEL_USE_CUSTOM_CONFIG and set BR2_LINUX_KERNEL_CUSTOM_CONFIG_FILE to the place where you want to save it (typically board/passkeeper/linux.config or $(BR2_EXTERNAL_PASSKEEPER)/board/passkeeper/linux.config if you are using an external).
    5. Run make linux-update-defconfig. It is essential you do this before doing anything else, otherwise Buildroot will complain that the file doesn't exist.