Re: [PATCH 3/3] docs: bootconfig: Add how to embed the bootconfig into kernel

Randy Dunlap
2022-03-13T17:52:54Z

Hi--

On 3/13/22 06:56, Masami Hiramatsu wrote:
> Add a description how to embed the bootconfig file into kernel.
>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> Documentation/admin-guide/bootconfig.rst | 31 +++++++++++++++++++++++++++---
> 1 file changed, 28 insertions(+), 3 deletions(-)
>
> diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
> index a1860fc0ca88..a172c669997a 100644
> --- a/Documentation/admin-guide/bootconfig.rst
> +++ b/Documentation/admin-guide/bootconfig.rst
> @@ -158,9 +158,15 @@ Each key-value pair is shown in each line with following style::
> Boot Kernel With a Boot Config
> ==============================
>
> -Since the boot configuration file is loaded with initrd, it will be added
> -to the end of the initrd (initramfs) image file with padding, size,
> -checksum and 12-byte magic word as below.
> +There are 2 options to boot the kernel with bootconfig, one is attaching
> +bootconfig to initrd image, and embedding the kernel itself.

There are two options to boot the kernel with bootconfig: attaching the
bootconfig to the initrd image or embedding it in the kernel itself.

> +
> +Attaching a Boot Config to Initrd
> +---------------------------------
> +
> +Since the boot configuration file is loaded with initrd by default,
> +it will be added to the end of the initrd (initramfs) image file with
> +padding, size, checksum and 12-byte magic word as below.
>
> [initrd][bootconfig][padding][size(le32)][checksum(le32)][#BOOTCONFIG\n]
>
> @@ -196,6 +202,25 @@ To remove the config from the image, you can use -d option as below::
> Then add "bootconfig" on the normal kernel command line to tell the
> kernel to look for the bootconfig at the end of the initrd file.
>
> +Embedding a Boot Config into Kernel
> +-----------------------------------
> +
> +If you can not use initrd, you can also embed the bootconfig file to the

in the

> +kernel by Kconfig options. In This case, you need to recompile the kernel

this

> +with the following configs::
> +
> + COFNIG_EMBED_BOOT_CONFIG=y
> + CONFIG_EMBED_BOOT_CONFIG_FILE="/PATH/TO/BOOTCONFIG/FILE"
> +
> +You need to set the correct path (relative path from kernel build directory
> +or absolute path) to the ``CONFIG_EMBED_BOOT_CONFIG_FILE`` option.
> +Then the kernel will embed the bootconfig file as a default bootconfig.
> +
> +As same as attaching to initrd, you need ``bootconfig`` option to the

Just as when attaching the bootconfig to the initrd, you need ``bootconfig`` option to the

> +kernel command line to enable the embedded bootconfig.
> +
> +Note that even if you set this option, you can override the embedded
> +bootconfig by another bootconfig which attached to the initrd.
>
> Kernel parameters via Boot Config
> =================================
>

HTH.

--
~Randy