ramroot for gentoo via initramfs

1. READ and CHANGE ramdisk.sh and gen_initramfs-ARCH.sh before deploying. This is just a script I made for myself, not a fully developed software.
2. ramdisk-TYPE.sh prepares root_fs. gen_initramfs-ARCH.sh packages new initramfs.img with the new init file.
3. MUST configure exclusions properly in _mount_dir@ramdisk, and make sure /mnt/.ramdisk is less than half your memory size. Make sure layouts of / and /mnt/.ramdisk/ are the same, e.g. merged-usr or not.

rsync -a /$1/ /mnt/.ramdisk/$1 --exclude src --exclude cache --exclude db --exclude portage --exclude python --exclude llvm --exclude repos --exclude binpkgs --exclude distfiles

3. /etc/genkernel.conf is with SYMLINK="yes". /usr/share/genkernel/gen_funcs.sh is for vfat boot.
4. Kernel is compiled by genkernel with "Support initial ramdisk/ramfs compressed using XZ".
5. The init file is modified from /usr/share/genkernel/defaults/linuxrc. It simply creates a tmpfs-based /ram_chroot synced from /mnt/.ramdisk/, and umount real_root before booting the real init via switch_root.

mkdir /ram_chroot
mount -t tmpfs -o rw,noatime none /ram_chroot
cp -a "${CHROOT}"/mnt/.ramdisk/* /ram_chroot/

mount --move /proc /ram_chroot/proc
mount --move /sys /ram_chroot/sys
mount --move /dev /ram_chroot/dev

umount ${CHROOT}

good_msg "Switching to real root: switch_root /ram_chroot ${init} ${init_opts}"
exec switch_root /ram_chroot "${init}"

6. gen_initramfs-ARCH.sh syncs kernel files from the server, packages the initramfs.img with new init, and deploys to /boot.
7. config.txt is for raspberry pi.

kernel kernel
initramfs initramfs followkernel

8. The script is for Gentoo. But it should work for Archlinux, if you re-generate init from /usr/lib/initcpio/init and package initramfs with zst.