[PATCH 2/2] Documentation: add extlinux.conf support description

[Ahmad Fatoum]

Hi,

On 4/16/26 3:45 PM, Alexander Shiyan wrote:
> Signed-off-by: Alexander Shiyan <eagle.alexander923 at gmail.com>

Thanks for adding documentation.

I have been wanting to add bootloader spec support to openembedded-core
to barebox can be used to boot Beaglebone black images generated by it,
but with extlinux support in barebox that should work as well.
I will surely give this a try in the future.

Could I motivate you to add a self test that exercises the parser?

Doesn't have to be anything extensive, see test/self/blspec.c for an
example. It's basically adding a few configs into the barebox
environment, calling bootentry_create_from_name() on the directory and
then running some assertions.

Thanks,
Ahmad

> ---
>  Documentation/user/booting-linux.rst | 38 ++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/Documentation/user/booting-linux.rst b/Documentation/user/booting-linux.rst
> index ed1ec3f68a..307f33bb22 100644
> --- a/Documentation/user/booting-linux.rst
> +++ b/Documentation/user/booting-linux.rst
> @@ -306,6 +306,44 @@ Additional notes about keys in the bootloader spec entries:
>     different devices without having to specify a different ``root=`` option each
>     time.
>  
> +.. _extlinux_conf:
> +
> +extlinux.conf Support
> +^^^^^^^^^^^^^^^^^^^^^
> +
> +In addition to the Boot Loader Specification, barebox also supports the
> +extlinux configuration format, commonly used by the Syslinux bootloader and
> +many Linux distributions. This format is often found on SD cards, USB drives,
> +or disk partitions prepared with tools like ``extlinux --install``.
> +
> +The configuration file is named ``extlinux.conf`` and can be located at:
> +* ``/boot/extlinux/extlinux.conf``
> +
> +The file uses a simple key-value syntax with sections labeled by ``LABEL``.
> +A typical example looks like:
> +
> +.. code-block:: none
> +
> +  DEFAULT linux
> +  LABEL linux
> +    KERNEL /boot/vmlinuz
> +    INITRD /boot/initrd.img
> +    FDT /boot/board.dtb
> +    APPEND console=ttyS0,115200 root=PARTUUID=deadbeef-01
> +
> +When booting an extlinux entry, barebox automatically strips any ``root=``
> +parameter from the ``APPEND`` line and injects the correct ``root=`` based on
> +the boot device (similar to the ``linux-appendroot`` feature in blspec). This
> +makes the same root filesystem image usable across different storage media.
> +
> +To use extlinux support, enable ``CONFIG_EXTLINUX`` in your barebox
> +configuration. Entries are automatically discovered by the :ref:`command_boot`
> +command when scanning a device or mount point. For example:
> +
> +.. code-block:: sh
> +
> +  boot mmc1.2
> +
>  .. _booting_linux_net:
>  
>  Network boot

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