Re: [docs] [PATCH] ref-manual/variables.rst: document the QB_DEFAULT_BIOS variable

Hi Antonin,

On 8/4/26 11:01 AM, Antonin Godard via lists.yoctoproject.org wrote:
> The QB_DEFAULT_BIOS allows setting the -bios parameter of QEMU, which
> can be used to emulate U-Boot, for example.
> 
> Signed-off-by: Antonin Godard <[email protected]>
> ---
>   documentation/ref-manual/variables.rst | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
> 
> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
> index e75f42afe..cfc764961 100644
> --- a/documentation/ref-manual/variables.rst
> +++ b/documentation/ref-manual/variables.rst
> @@ -8084,6 +8084,18 @@ system and gives an overview of their function and contents.
>         replaces the ``@CLIENT@`` and ``@GATEWAY@`` place holders by the IP and
>         the gateway address of the QEMU guest.
>   
> +   :term:`QB_DEFAULT_BIOS`
> +      the `QB_DEFAULT_BIOS` variable can be used to add the ``-bios`` option to
> +      the initialization parameters of QEMU. For example, this parameter can be

No. It is the path of the file relative to DEPLOY_DIR_IMAGE that is then 
passed to QEMU via the -bios option. The wording here seems to imply 
that setting this variable passes -bios as a parameter to QEMU and 
that's it.

Also this only applies if BIOS is not set otherwise it takes precedence 
and this variable isn't actually used. We probably take this opportunity 
to document this variable as it'll achieve the same goal as 
QB_DEFAULT_BIOS, just that it takes precedence over it and that it'll 
expect a path differently formatted than QB_DFAULT_BIOS which expects it 
to be in DEPLOY_DIR_IMAGE (unclear if BIOS can be a relative path (and 
relative to which directory) or if it needs to be absolute (which is 
disastrous for reusability across machines).

I\m traveling currently so cannot check, but is there a link to the QEMU 
docs to explain what this -bios argument should be set to by any chance? 
If there is one, it'd be nice to add a link to it here.

> +      set as follows to emulate U-Boot for the :oecore_path:`qemuarm64
> +      <meta/conf/machine/qemuarm64.conf>` machine::
> +
> +         QB_DEFAULT_BIOS = "u-boot.bin"
> +
> +      The above example makes the assumption you have built the U-Boot recipe
> +      and that the ``u-boot.bin`` file is located in the

s/is located in the/deployed to the root directory at/ ?

Cheers,
Quentin