This is a init script for initramfs/initrd which parses rootfs given by LABEL/UUID.

init.sh

#!/bin/busybox sh
# Init for initram.
# by Jerry Fleming <[email protected]> on 2013-03-25.
# No rights reserved. Use at your own risk.

# utility functions {{{
rescue_shell()
{
    echo "Something went wrong. Dropping you to a shell."
    echo "Please switch root manually."
    busybox --install -s /bin
    exec /bin/sh
}

mount_root()
{
    for cmd in $(cat /proc/cmdline) ; do
        case $cmd in
        root=*)
            root=$(echo $cmd | cut -d= -f2)
            if [ $root == "LABEL" ] || [ $root == "UUID" ] ; then
                param=$(echo $cmd | cut -d= -f2-3)
                root=
                cnt=1
                while [ -z $root ]
                do
                    echo "Probing rootfs ($cnt) ..."
                    cnt=$(($cnt+1))
                    sleep 3
                    root=$(findfs $param)
                    if [ $cnt -gt 20 ]
                    then
                        echo "Max tries reached, still can't find rootfs."
                        rescue_shell
                    fi
                done
            fi
            mount -o ro $root /mnt/root || rescue_shell
            ;;
        esac
    done
}
# utility functions }}}

echo "Initializing ramfs to boot rootfs."

# Mount the /proc and /sys filesystems.
mount -t proc none /proc
mount -t sysfs none /sys

# Do your stuff here: loading disk drivers.
mount_root

# Clean up.
umount /proc
umount /sys

# Boot the real thing.
exec switch_root /mnt/root /sbin/init