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When installed, this module mounts a read-write (RW) overlay on top of a root filesystem, which is kept read-only (RO), free from modifications by the user, this might prove to be useful if we want to access or restore the original unmodified rootfs. The existing overlay-etc.bbclass does something similar, it mounts an overlay on top of the /etc directory, however doing the same for root causes the original root to be inaccessible once the system is booted, hence why this module is added to the initramfs boot flow, allowing us to mount the RW overlay, while keeping the original rootfs mounted at /rofs once the system finishes booting. This script is loosely based on that class. This module requires rootrw=<foo> to be passed as a kernel parameter to specify the device/partition to be used as RW by the overlay and has a dependency on overlayfs support being present in the running kernel. It does not require the read-only IMAGE_FEATURE to be enabled. The module needs to be executed after the initramfs-module-rootfs since it relies on it to mount the filesystem at initramfs startup but before the finish module which normally switches root. After overlayroot is executed the usual boot flow continues from the real init process. If something goes wrong while running this module, the rootfs is still mounted RO (with no overlay) and the finish module is executed to continue booting normally. Its worth noting that, on purpose, this isnt installed by default on any images that use initramfs-framework to keep the boot flow unmodified, only when a user manually requests to install it, then it becomes functional. (From OE-Core rev: 4f876982a856c54a8074c85346632e33caa7ef53) Signed-off-by: Alejandro Enedino Hernandez Samaniego <alhe@linux.microsoft.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Poky
Poky is an integration of various components to form a pre-packaged build system and development environment which is used as a development and validation tool by the Yocto Project. It features support for building customised embedded style device images and custom containers. There are reference demo images ranging from X11/GTK+ to Weston, commandline and more. The system supports cross-architecture application development using QEMU emulation and a standalone toolchain and SDK suitable for IDE integration.
Additional information on the specifics of hardware that Poky supports is available in README.hardware. Further hardware support can easily be added in the form of BSP layers which extend the systems capabilities in a modular way. Many layers are available and can be found through the layer index.
As an integration layer Poky consists of several upstream projects such as BitBake, OpenEmbedded-Core, Yocto documentation, the 'meta-yocto' layer which has configuration and hardware support components. These components are all part of the Yocto Project and OpenEmbedded ecosystems.
The Yocto Project has extensive documentation about the system including a reference manual which can be found at https://docs.yoctoproject.org/
OpenEmbedded is the build architecture used by Poky and the Yocto project. For information about OpenEmbedded, see the OpenEmbedded website.
Contribution Guidelines
The project works using a mailing list patch submission process. Patches should be sent to the mailing list for the repository the components originate from (see below). Throughout the Yocto Project, the README files in the component in question should detail where to send patches, who the maintainers are and where bugs should be reported.
A guide to submitting patches to OpenEmbedded is available at:
https://www.openembedded.org/wiki/How_to_submit_a_patch_to_OpenEmbedded
There is good documentation on how to write/format patches at:
https://www.openembedded.org/wiki/Commit_Patch_Message_Guidelines
Where to Send Patches
As Poky is an integration repository (built using a tool called combo-layer), patches against the various components should be sent to their respective upstreams:
OpenEmbedded-Core (files in meta/, meta-selftest/, meta-skeleton/, scripts/):
- Git repository: https://git.openembedded.org/openembedded-core/
- Mailing list: openembedded-core@lists.openembedded.org
BitBake (files in bitbake/):
- Git repository: https://git.openembedded.org/bitbake/
- Mailing list: bitbake-devel@lists.openembedded.org
Documentation (files in documentation/):
- Git repository: https://git.yoctoproject.org/cgit/cgit.cgi/yocto-docs/
- Mailing list: docs@lists.yoctoproject.org
meta-yocto (files in meta-poky/, meta-yocto-bsp/):
- Git repository: https://git.yoctoproject.org/cgit/cgit.cgi/meta-yocto
- Mailing list: poky@lists.yoctoproject.org
If in doubt, check the openembedded-core git repository for the content you intend to modify as most files are from there unless clearly one of the above categories. Before sending, be sure the patches apply cleanly to the current git repository branch in question.