[v2] ref-manual/variables.rst: expand IMAGE_OVERHEAD_FACTOR glossary entry

From: Joao Marcos Costa <joaomarcos.costa@bootlin.com>

There's a (second) overhead factor applied in images generated with Wic,
and this is already documented in the .wks reference. However, the
IMAGE_OVERHEAD_FACTOR entry does not mention it, and by looking at the
partition sizes (e.g. with parted) one may find it confusing that they
don't match with the expected rootfs size (e.g. in a scenario where the
extra space is "0" and IMAGE_OVERHEAD_FACTOR="1.0").

This second overhead is already documented, though:
https://docs.yoctoproject.org/ref-manual/kickstart.html#command-part-or-partition

Mention the '--overhead-factor' option in the glossary entry and add a
reference to the wks documentation.

Signed-off-by: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
---
 documentation/ref-manual/variables.rst | 5 +++++
 1 file changed, 5 insertions(+)

Hi João,

On 9/1/25 5:35 PM, joaomarcos.costa@bootlin.com wrote:
> From: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
> 
> There's a (second) overhead factor applied in images generated with Wic,
> and this is already documented in the .wks reference. However, the
> IMAGE_OVERHEAD_FACTOR entry does not mention it, and by looking at the
> partition sizes (e.g. with parted) one may find it confusing that they
> don't match with the expected rootfs size (e.g. in a scenario where the
> extra space is "0" and IMAGE_OVERHEAD_FACTOR="1.0").
> 
> This second overhead is already documented, though:
> https://docs.yoctoproject.org/ref-manual/kickstart.html#command-part-or-partition
> 
> Mention the '--overhead-factor' option in the glossary entry and add a
> reference to the wks documentation.
> 
> Signed-off-by: Joao Marcos Costa <joaomarcos.costa@bootlin.com>
> ---
>   documentation/ref-manual/variables.rst | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
> index d559899c6..b7fd1cc5e 100644
> --- a/documentation/ref-manual/variables.rst
> +++ b/documentation/ref-manual/variables.rst
> @@ -4166,6 +4166,11 @@ system and gives an overview of their function and contents.
>         added to the image by using the :term:`IMAGE_ROOTFS_EXTRA_SPACE`
>         variable.
>   
> +      When using Wic tool, beware that a second overhead factor is also applied.
> +      This overhead value is defined by the ``--overhead-factor`` option, which
> +      defaults to "1.3" when omitted. See the ":doc:`/ref-manual/kickstart`"
> +      (Command: part or partition) chapter for details.
> +

"""
See :ref:`ref-manual/kickstart:command: part or partition` chapter in 
the OpenEmbedded Kickstart reference section.
"""

or even

"""
See :ref:`ref-manual/kickstart:command: part or partition` chapter in 
:doc:`/ref-manual/kickstart`.
"""

if you prefer.

Otherwise, looks fine to me, so with that:

Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>

Thanks!
Quentin