#!/bin/sh
#
# This program reads the bcache superblock on bcacheX slaves to extract the
# dev.uuid and dev.label which refer to a specific backing device.
#
# It integrates with udev 'import' by writing CACHED_UUID=X and optionally
# CACHED_LABEL=X for the backing device of the provided bcache device.
# Ignore caching devices by skipping unless sb.version=1
#
# There is 1 and only 1 backing device (slaves/*) for a bcache device.

TEMPNODE=${1}  # /dev/bcacheN
DEVNAME=${TEMPNODE##*/}  # /dev/bcacheN -> bcacheN

for slave in "/sys/class/block/$DEVNAME/slaves"/*; do
    [ -d "$slave" ] || continue
    bcache-super-show "/dev/${slave##*/}" |
       awk '$1 == "sb.version" { sbver=$2; }
            $1 == "dev.uuid" { uuid=$2; }
            $1 == "dev.label" && $2 != "(empty)" { label=$2; }
            END {
                if ((sbver == 1 || sbver == 4 || sbver == 6) && uuid) {
                    print("CACHED_UUID=" uuid)
                    if (label) print("CACHED_LABEL=" label)
                    exit(0)
                }
                exit(1);
            }'
    # awk exits 0 if it found a backing device.
    [ $? -eq 0 ] && exit 0
done