FM / udev

/usr/lib/udev

Name	Size	Mode	Actions
hwdb.d/	-	0755	rm
rules.d/	-	0755	rm
ata_id	63824	0755	edit dl rm
bcache-export-cached	1155	0755	edit dl rm
bcache-register	14488	0755	edit dl rm
cdrom_id	80216	0755	edit dl rm
dmsetup_env	833	0755	edit dl rm
fido_id	96768	0755	edit dl rm
hdparm	1399	0755	edit dl rm
hwclock-set	776	0755	edit dl rm
hwdb.bin	9956330	0444	edit dl rm
kpartx_id	2383	0755	edit dl rm
mtd_probe	18600	0755	edit dl rm
probe-bcache	14488	0755	edit dl rm
scsi_id	80776	0755	edit dl rm
snappy-app-dev	43248	0755	edit dl rm
v4l_id	18680	0755	edit dl rm

Edit: /usr/lib/udev/bcache-export-cached (1155B)

#!/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
    /usr/sbin/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 && 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

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