linux-kernel - Re: [PATCH v2 3/3] docs: bootconfig: Add how to embed the bootconfig into kernel

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Message-ID: <8ad1fb98-3141-1e57-b627-0c8184fef955@infradead.org>
Date:   Sun, 13 Mar 2022 19:03:20 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     Padmanabha Srinivasaiah <treasure4paddy@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 3/3] docs: bootconfig: Add how to embed the bootconfig
 into kernel



On 3/13/22 18:54, Masami Hiramatsu wrote:
> Add a description how to embed the bootconfig file into kernel.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  Changes in v2:
>   - Corrected the text accoding to Randy's suggestion.
>   - Do not reccomend to use relative path for CONFIG_EMBED_BOOT_CONFIG_FILE.
> ---
>  Documentation/admin-guide/bootconfig.rst |   30 +++++++++++++++++++++++++++---
>  1 file changed, 27 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/admin-guide/bootconfig.rst b/Documentation/admin-guide/bootconfig.rst
> index a1860fc0ca88..1af1a172fdd4 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 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 +202,24 @@ 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 in the
> +kernel by Kconfig options. In this case, you need to recompile the kernel
> +with the following configs::
> +
> + COFNIG_EMBED_BOOT_CONFIG=y

    CONFIG_

> + CONFIG_EMBED_BOOT_CONFIG_FILE="/PATH/TO/BOOTCONFIG/FILE"
> +
> +``CONFIG_EMBED_BOOT_CONFIG_FILE`` requires a correct absolute path to
> +the bootconfig file. The kernel will embed it as the default bootconfig.
> +
> +Just as when attaching the bootconfig to the initrd, you need ``bootconfig``
> +option to the kernel command line to enable the embedded bootconfig.

          on the

preferably.

> +
> +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
>  =================================
> 

thanks.
-- 
~Randy