[PATCH 1/3] meta/classes: Generate a custom initramfs

["Q. Gylstorff" <Quirin.Gylstorff@siemens.com>]

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

This class sets the Parameters for mkinitramfs before it overwrites
 the initrd.img of debian with a modified version.

Use cases are the remove unnecessary kernel modules to reduce the
size of the initrd by using the parameters:
```
INITRAMFS_MODULES = "list"
INITRAMFS_MODULE_LIST += "ext4"
```

Set the boot root during the initrd generation by setting `INITRAMFS_ROOT`.

see also man pages of mkinitramfs and initramfs.conf.

Signed-off-by: Quirin Gylstorff <quirin.gylstorff@siemens.com>
---
 meta/classes/initramfs.bbclass | 44 ++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 meta/classes/initramfs.bbclass

diff --git a/meta/classes/initramfs.bbclass b/meta/classes/initramfs.bbclass
new file mode 100644
index 0000000..0cc91c2
--- /dev/null
+++ b/meta/classes/initramfs.bbclass
@@ -0,0 +1,44 @@
+# This software is a part of ISAR.
+# Copyright (C) 2020 Siemens AG
+#
+# SPDX-License-Identifier: MIT
+
+INITRAMFS_MODULES ?= "most"
+INITRAMFS_BUSYBOX ?= "auto"
+INITRAMFS_COMPRESS ?= "gzip"
+INITRAMFS_KEYMAP ?= "n"
+INITRAMFS_NET_DEVICE ?= ""
+INITRAMFS_NFSROOT ?= "auto"
+INITRAMFS_RUNSIZE ?= "10%"
+INITRAMFS_ROOT ?= ""
+INITRAMFS_MODULE_LIST ?= ""
+update_initramfs_modules() {
+   for modname in ${INITRAMFS_MODULE_LIST}; do
+     sudo -E tee --append '${ROOTFSDIR}/etc/initramfs-tools/modules' << EOF
+${modname}
+EOF
+   done
+}
+update_initramfs_config() {
+    sudo -E tee ${ROOTFSDIR}/etc/initramfs-tools/initramfs.conf << EOF
+MODULES=${INITRAMFS_MODULES}
+BUSYBOX=${INITRAMFS_BUSYBOX}
+COMPRESS=${INITRAMFS_COMPRESS}
+KEYMAP=${INITRAMFS_KEYMAP}
+DEVICE=${INITRAMFS_NET_DEVICE}
+NFSROOT=${INITRAMFS_NFSROOT}
+RUNSIZE=${INITRAMFS_RUNSIZE}
+ROOT=${INITRAMFS_ROOT}
+EOF
+}
+
+do_update_initramfs() {
+  update_initramfs_modules
+  update_initramfs_config
+  export KERNEL_VERSION=$(ls ${ROOTFSDIR}/lib/modules)
+  bbplain kernel_version: ${KERNEL_VERSION}
+  sudo -E chroot '${ROOTFSDIR}' \
+      mkinitramfs -v -k -o /boot/initrd.img-${KERNEL_VERSION} ${KERNEL_VERSION}
+}
+
+addtask update_initramfs before do_copy_boot_files after do_rootfs_install
-- 
2.20.1