[isar-cip-core][RFC v4 3/3] copy and symlink dpkg db to ro-rootfs

[Felix Moessbauer <felix.moessbauer@siemens.com>]

The dpkg database is located on the var partition, but this partition is
not updated (and might not even be deployed). To still have information
about what is installed, we relocate the database to /usr/share and
create a symlink using tmpdirs.d.

Note, that this is only enabled on debian bookworm, as the proper
packaging of tmpdirs files is only supported from debhelper-compat 13
on.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
---
 classes/read-only-rootfs.bbclass              | 10 ++++++++
 .../files/immutable-rootfs.tmpfiles           |  1 +
 .../immutable-rootfs/immutable-rootfs_0.1.bb  | 23 +++++++++++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 recipes-core/immutable-rootfs/files/immutable-rootfs.tmpfiles
 create mode 100644 recipes-core/immutable-rootfs/immutable-rootfs_0.1.bb

diff --git a/classes/read-only-rootfs.bbclass b/classes/read-only-rootfs.bbclass
index 6f91f66..bb8ab9a 100644
--- a/classes/read-only-rootfs.bbclass
+++ b/classes/read-only-rootfs.bbclass
@@ -17,6 +17,16 @@ do_image_wic[depends] += "${INITRAMFS_RECIPE}:do_build"
 IMAGE_INSTALL += "home-fs"
 IMAGE_INSTALL += "tmp-fs"
 
+# For pre bookworm images, empty /var is not usable
+IMAGE_INSTALL:append:bookworm = " immutable-rootfs"
+
+ROOTFS_POSTPROCESS_COMMAND:append:bookworm =" copy_dpkg_state"
+copy_dpkg_state() {
+    IMMUTABLE_VAR_LIB="${ROOTFSDIR}/usr/share/immutable-data/var/lib"
+    sudo mkdir -p "$IMMUTABLE_VAR_LIB"
+    sudo cp -a ${ROOTFSDIR}/var/lib/dpkg "$IMMUTABLE_VAR_LIB/"
+}
+
 image_configure_fstab() {
     sudo tee '${IMAGE_ROOTFS}/etc/fstab' << EOF
 # Begin /etc/fstab
diff --git a/recipes-core/immutable-rootfs/files/immutable-rootfs.tmpfiles b/recipes-core/immutable-rootfs/files/immutable-rootfs.tmpfiles
new file mode 100644
index 0000000..d180bc5
--- /dev/null
+++ b/recipes-core/immutable-rootfs/files/immutable-rootfs.tmpfiles
@@ -0,0 +1 @@
+L /var/lib/dpkg - - - - /usr/share/immutable-data/var/lib/dpkg
diff --git a/recipes-core/immutable-rootfs/immutable-rootfs_0.1.bb b/recipes-core/immutable-rootfs/immutable-rootfs_0.1.bb
new file mode 100644
index 0000000..2dbda6d
--- /dev/null
+++ b/recipes-core/immutable-rootfs/immutable-rootfs_0.1.bb
@@ -0,0 +1,23 @@
+#
+# CIP Core, generic profile
+#
+# Copyright (c) Siemens AG, 2024
+#
+# Authors:
+#  Felix Moessbauer <felix.moessbauer@siemens.com>
+#
+# SPDX-License-Identifier: MIT
+
+# Note: This requires debhelper-compat 13, which limits it to bookworm
+
+inherit dpkg-raw
+
+MAINTAINER = "Felix Moessbauer <felix.moessbauer@siemens.com>"
+DESCRIPTION = "Config to link volatile data to immutable copies"
+
+SRC_URI = "file://${BPN}.tmpfiles"
+DPKG_ARCH = "all"
+
+do_prepare_build:append() {
+    cp ${WORKDIR}/${BPN}.tmpfiles ${S}/debian/
+}
-- 
2.39.2