diff mbox series

[v1,3/3] classes: add a systemd-sysext image class

Message ID 20240213085658.170917-4-johannes.schneider@leica-geosystems.com
State New
Headers show
Series pkg-database and systemd-sysext image | expand

Commit Message

Johannes Schneider Feb. 13, 2024, 8:56 a.m. UTC 
systemd-sysext can load a raw-image containing usr/ and opt/ folders
to mount them as RO overlay over the rootfs, to "extend" the systems.

This class provides the necessary changes/additions to the enclosed
file-system so that systemd-sysext accepts the extension for "merge"
into the rootfs.

With such an created image, placed into the correct folder (see [1]),
`systemd-sysext list` should be able to list the "extension" and
`systemd-sysext merge` should enable the overlay. On both commands a
preceding "SYSTEMD_LOG_LEVEL=debug" can aide in figuring out what is
amiss.

The strict name checking systemd-sysext does against the name of
extension-release.NAME file, is disabled, as there is only one such in
the resulting image. This is done to allow a user to freely rename the
resulting image file.
Note that for e.g. squashfs, the kernel needs CONFIG_SQUASHFS_XATTR=y

Link: https://www.freedesktop.org/software/systemd/man/latest/systemd-sysext.html
Link: https://0pointer.net/blog/testing-my-system-code-in-usr-without-modifying-usr.html
Signed-off-by: Johannes Schneider <johannes.schneider@leica-geosystems.com>
---
 meta/classes/image-sysext.bbclass | 38 +++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 meta/classes/image-sysext.bbclass
diff mbox series

Patch

diff --git a/meta/classes/image-sysext.bbclass b/meta/classes/image-sysext.bbclass
new file mode 100644
index 0000000000..10dcb267a5
--- /dev/null
+++ b/meta/classes/image-sysext.bbclass
@@ -0,0 +1,42 @@ 
+# SPDX-License-Identifier: MIT
+#
+# Copyright Leica Geosystems AG
+#
+
+# systemd-sysext [1] has a simple mechanism for version compatibility:
+# the extension to be loaded has to contain a
+# /usr/lib/extension-release.d/extension-release.NAME
+# with "NAME" *exactly* matching the filename of the extensions
+# raw-device filename/
+#
+# from the extension-release file the "ID" and "VERSION_ID" fields are
+# matched against the etc/os-release and the extension is only "merged"
+# if no mismatches between NAME, ID, and VERSION_ID.
+#
+# Link: https://www.freedesktop.org/software/systemd/man/latest/systemd-sysext.html
+
+inherit image
+
+IMAGE_NAME_SUFFIX = ".sysext"
+EXTENSION_NAME = "${IMAGE_NAME}${IMAGE_NAME_SUFFIX}.${IMAGE_FSTYPES}"
+
+DEPENDS += " os-release"
+
+sysext_image_mangle_rootfs() {
+    R=${IMAGE_ROOTFS}
+
+    # pull a copy of the rootfs version information, which systemd-sysext matches against
+    cp -av ${RECIPE_SYSROOT}/${nonarch_libdir}/os-release ${WORKDIR}/extension-release.base
+
+    echo 'EXTENSION_RELOAD_MANAGER=1' >> ${WORKDIR}/extension-release.base
+
+    install -d $R${nonarch_libdir}/extension-release.d
+    install -m 0644 ${WORKDIR}/extension-release.base \
+        $R${nonarch_libdir}/extension-release.d/extension-release.${EXTENSION_NAME}
+
+    # disable systemd-sysext's strict name checking, so that the image file can be renamed, while still being 'merge'-able
+    setfattr -n user.extension-release.strict -v false \
+        $R${nonarch_libdir}/extension-release.d/extension-release.${EXTENSION_NAME}
+}
+
+ROOTFS_POSTPROCESS_COMMAND += " sysext_image_mangle_rootfs; "