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ref-manual: add overlayfs-etc class

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(From yocto-docs rev: c11da26609e02f0c0b43efacb4642141d990ebaa)

Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
Reviewed-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
This commit is contained in:
Vyacheslav Yurkov
2021-12-16 12:22:34 +01:00
committed by Richard Purdie
parent 7c7e53570c
commit 4b2d79d740
1 changed files with 46 additions and 0 deletions
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documentation/ref-manual/classes.rst
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@@ -1769,6 +1769,52 @@ to the unit the following::
.. note::
The class does not support the ``/etc`` directory itself, because ``systemd`` depends on it.
In order to get ``/etc`` in overlayfs, see :ref:`overlayfs-etc <ref-classes-overlayfs-etc>`.
.. _ref-classes-overlayfs-etc:
``overlayfs-etc.bbclass``
=========================
In order to have the ``/etc`` directory in overlayfs a special handling at early
boot stage is required. The idea is to supply a custom init script that mounts
``/etc`` before launching the actual init program, because the latter already
requires ``/etc`` to be mounted.
Example usage in image recipe::
IMAGE_FEATURES += "overlayfs-etc"
.. note::
This class must not be inherited directly. Use :term:`IMAGE_FEATURES` or :term:`EXTRA_IMAGE_FEATURES`
Your machine configuration should define at least the device, mount point, and file system type
you are going to use for ``overlayfs``::
OVERLAYFS_ETC_MOUNT_POINT = "/data"
OVERLAYFS_ETC_DEVICE = "/dev/mmcblk0p2"
OVERLAYFS_ETC_FSTYPE ?= "ext4"
To control more mount options you should consider setting mount options
(``defaults`` is used by default)::
OVERLAYFS_ETC_MOUNT_OPTIONS = "wsync"
The class provides two options for ``/sbin/init`` generation:
- The default option is to rename the original ``/sbin/init`` to ``/sbin/init.orig``
and place the generated init under original name, i.e. ``/sbin/init``. It has an advantage
that you won't need to change any kernel parameters in order to make it work,
but it poses a restriction that package-management can't be used, because updating
the init manager would remove the generated script.
- If you wish to keep original init as is, you can set::
OVERLAYFS_ETC_USE_ORIG_INIT_NAME = "0"
Then the generated init will be named ``/sbin/preinit`` and you would need to extend your
kernel parameters manually in your bootloader configuration.
.. _ref-classes-own-mirrors: