From: "Vyacheslav Yurkov" <uvv.mail@gmail.com>
To: docs@lists.yoctoproject.org
Cc: Vyacheslav Yurkov <uvv.mail@gmail.com>
Subject: [PATCH] ref-manual: add overlayfs class
Date: Sat, 14 Aug 2021 06:28:25 +0200 [thread overview]
Message-ID: <20210814042825.124630-1-uvv.mail@gmail.com> (raw)
Signed-off-by: Vyacheslav Yurkov <uvv.mail@gmail.com>
---
documentation/ref-manual/classes.rst | 46 ++++++++++++++++++++++++++++
1 file changed, 46 insertions(+)
diff --git a/documentation/ref-manual/classes.rst b/documentation/ref-manual/classes.rst
index a98a64c43..5d33e81a1 100644
--- a/documentation/ref-manual/classes.rst
+++ b/documentation/ref-manual/classes.rst
@@ -1710,6 +1710,52 @@ one such example. However, being aware of this class can reduce the
proliferation of different versions of similar classes across multiple
layers.
+.. _ref-classes-overlayfs:
+
+``overlayfs.bbclass``
+=======================
+
+
+It's often desired in Embedded System design to have a read-only rootfs.
+But a lot of different applications might want to have a read-write access to
+some parts of a filesystem. It can be especially useful when your update mechanism
+overwrites the whole rootfs, but you want your application data to be preserved
+between updates. The ``overlayfs`` class provides a way to achieve that by means
+of overlayfs and at the same time keeping the base rootfs read-only.
+
+To use this class, set a mount point for a partition overlayfs is going to use as upper
+layer in your machine configuration. Underlying file system can be anything that
+is supported by overlayfs. This has to be done in your machine configuration::
+
+ OVERLAYFS_MOUNT_POINT[data] = "/data"
+
+.. note::
+
+ QA check fails to catch file existence if you redefine this variable in your recipe!
+
+The class assumes you have a data.mount systemd unit defined elsewhere in your BSP
+(e.g. in systemd-machine-units recipe) and it's installed to the image.
+
+Then you can specify writable directories on a recipe basis::
+
+ OVERLAYFS_WRITABLE_PATHS[data] = "/usr/share/my-custom-application"
+
+To support several mount points you can use a different variable flag. Assume we
+want to have a writable location on the file system, but not interested where the data
+survive a reboot. Then we could have a mnt-overlay.mount unit for a tmpfs file system.
+
+In your machine configuration::
+
+ OVERLAYFS_MOUNT_POINT[mnt-overlay] = "/mnt/overlay"
+
+and then in your recipe::
+
+ OVERLAYFS_WRITABLE_PATHS[mnt-overlay] = "/usr/share/another-application"
+
+.. note::
+
+ The class does not support /etc directory itself, because systemd depends on it
+
.. _ref-classes-own-mirrors:
``own-mirrors.bbclass``
--
2.28.0
next reply other threads:[~2021-08-14 4:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-14 4:28 Vyacheslav Yurkov [this message]
2021-08-16 9:14 ` [docs] [PATCH] ref-manual: add overlayfs class Quentin Schulz
2021-08-17 3:29 ` Vyacheslav Yurkov
2021-08-17 8:37 ` Quentin Schulz
2021-08-17 13:47 ` Vyacheslav Yurkov
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