tinyramfs/device-helper

#!/bin/sh -f
#
# create /dev/disk/by-* and /dev/mapper/* symlinks

create_symlink()
{
    dir="$1"; sym="$2"

    sym="${sym%\"}"
    sym="${sym#\"}"
    sym="${dir}/${sym}"

    mkdir -p "$dir"
    ln    -s "../../${dev_name}" "$sym"
}

[ -b "/dev/${dev_name=${DEVPATH##*/}}" ] || exit 1

exec > /dev/null 2>&1

read -r dm_name < "/sys/block/${dev_name}/dm/name" && {
    mkdir -p /dev/mapper
    ln    -sf "../${dev_name}" "/dev/mapper/${dm_name:?}"
}

command -v blkid || exit 0

# prevent race condition
blkid "/dev/${dev_name}" || sleep 2

for line in $(blkid "/dev/${dev_name}"); do case   "${line%%=*}" in
    UUID)     create_symlink /dev/disk/by-uuid     "${line##*=}" ;;
    LABEL)    create_symlink /dev/disk/by-label    "${line##*=}" ;;
    PARTUUID) create_symlink /dev/disk/by-partuuid "${line##*=}" ;;
esac; done