[RFC PATCH] meta/classes: Add strip-image

["'Quirin Gylstorff' via isar-users" <isar-users@googlegroups.com>]

From: Quirin Gylstorff <quirin.gylstorff@siemens.com>

This class provides the optional functionality to strip packages
and files from a image. This allows the user to reduce the image
size.

IMPORTANT: This is an expert feature and can lead to broken images.
Signed-off-by: Quirin Gylstorff <quirin.gylstorff@siemens.com>
---

The default settings will reduce the space around 40MB. It is currently
a RFC to collect information about the usage.

Should we integrate by default or should the user add this on demand?
For a default integration I would drop the deletion:
 - /vmlinuz*
 - /boot
 - /usr/include
 - initramfs-tools

 meta/classes/strip-image.bbclass | 64 ++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 meta/classes/strip-image.bbclass

diff --git a/meta/classes/strip-image.bbclass b/meta/classes/strip-image.bbclass
new file mode 100644
index 00000000..edff3fd4
--- /dev/null
+++ b/meta/classes/strip-image.bbclass
@@ -0,0 +1,64 @@
+# strip image helper
+#
+# This software is a part of ISAR.
+# Copyright (C) Siemens AG, 2025
+#
+# SPDX-License-Identifier: MIT
+# This class provides functions to remove pacakges and files
+# from the image
+
+# Default list of files to be removed:
+#  - remove kernel and initrd
+#  - remove all documentation
+#  - remove all include files
+IMAGE_STRIP_FILES += " \
+    /vmlinuz* \
+    /boot \
+    /usr/share/doc \
+    /usr/share/info \
+    /usr/share/man \
+    /usr/include \
+"
+
+do_strip_files_from_image[vardeps] = "${IMAGE_STRIP_FILES}"
+do_strip_files_from_image[network] = "${TASK_USE_SUDO}"
+do_strip_files_from_image() {
+i    if [ -n "${IMAGE_STRIP_FILES}" ]; then
+        cat <<EOF | sudo tee "${IMAGE_ROOTFS}/purge.sh"
+#!/usr/bin/env sh
+set -x
+for elem in ${IMAGE_STRIP_FILES}; do
+    find \$elem ! -type d -exec rm -rf {} \;
+done
+rm -f /purge.sh
+EOF
+        sudo chmod 755 "${IMAGE_ROOTFS}/purge.sh"
+        sudo -E chroot "${IMAGE_ROOTFS}" "/purge.sh"
+    fi
+}
+addtask strip_files_from_image before do_rootfs_finalize after do_generate_initramfs
+IMAGE_STRIP_PACKAGES += " \
+    initramfs-tools \
+    initramfs-tools-core \
+    locales \
+"
+do_strip_packages_from_image[vardeps] = "${IMAGE_STRIP_PACKAGES}"
+do_strip_packages_from_image[network] = "${TASK_USE_SUDO}"
+do_strip_packages_from_image() {
+    bbnote "IMAGE_PACKAGES_REMOVE: ${IMAGE_PACKAGES_REMOVE}"
+    if [ -n "${IMAGE_STRIP_PACKAGES}" ]; then
+        RMPKGS=$(dpkg-query \
+            --admindir=${IMAGE_ROOTFS}/var/lib/dpkg/ \
+            -f '${Package}\n' \
+            -W ${IMAGE_STRIP_PACKAGES} 2>/dev/null || true)
+
+        if [ -n "${RMPKGS}" ]; then
+            bbnote "Removing packages: ${RMPKGS}"
+            sudo -E chroot "${IMAGE_ROOTFS}" \
+                dpkg --purge --force-depends --force-remove-essential ${RMPKGS}
+        else
+            bbnote "Packages have already been purged or could not be found"
+        fi
+    fi
+}
+addtask strip_packages_from_image before do_strip_files_from_image do_rootfs_finalize after do_rootfs_postprocess
-- 
2.50.1

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