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

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Message-Id: <20220314170333.0311c13a654c63d7ebe68e1f@kernel.org>
Date:   Mon, 14 Mar 2022 17:03:33 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        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 Sun, 13 Mar 2022 19:03:20 -0700
Randy Dunlap <rdunlap@...radead.org> wrote:

> 
> 
> 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_

Oops, it's a typo...

> 
> > + 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

OK.

Thank you!

> 
> 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


-- 
Masami Hiramatsu <mhiramat@...nel.org>