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[v3] ref-manual/variables.rst: expand IMAGE_OVERHEAD_FACTOR glossary entry

Message ID 20250901160759.556662-1-joaomarcos.costa@bootlin.com
State Under Review
Headers show
Series [v3] ref-manual/variables.rst: expand IMAGE_OVERHEAD_FACTOR glossary entry | expand

Commit Message

Joao Marcos Costa Sept. 1, 2025, 4:07 p.m. UTC 
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 | 6 ++++++
 1 file changed, 6 insertions(+)
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Patch

diff --git a/documentation/ref-manual/variables.rst b/documentation/ref-manual/variables.rst
index d559899c6..18ead7d04 100644
--- a/documentation/ref-manual/variables.rst
+++ b/documentation/ref-manual/variables.rst
@@ -4166,6 +4166,12 @@  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
+      :ref:`ref-manual/kickstart:command: part or partition` chapter in
+      :doc:`/ref-manual/kickstart` for details.
+
    :term:`IMAGE_PKGTYPE`
       Defines the package type (i.e. DEB, RPM or IPK) used by the
       OpenEmbedded build system. The variable is defined appropriately by