#!/bin/bash

#sources:
#https://wiki.archlinux.org/title/bcache
#https://stackoverflow.com/questions/20797819/command-to-change-the-default-home-directory-of-a-user
#https://unix.stackexchange.com/questions/156102/optimizing-bcache
#https://evilpiepirate.org/git/linux-bcache.git/tree/Documentation/bcache.txt

#Block device for caching (e.g. disk or partition):
ssddev=/dev/sdb

#Block device to use with cache:
hdddev=/dev/sdc

#Name of the mounted device:
mountname=/mnt/bcache

#Cache setting for sequential writes
#There is an issue with parsing prefixes, max 4 GB, use 0 for no cutoff
sequential_cutoff=0

set -e

if [ "$EUID" -ne 0 ]; then
  echo "Please run as root"
  exit
fi

read -p "Block devices $ssddev and $hdddev will be wiped, are you sure proceed?" -n 1 -r
echo
if [[ ! $REPLY =~ ^[Yy]$ ]]; then
  exit
fi

while [ -b /dev/bcache0 ]; then
  echo "Canceld, device /dev/bcache0 is allready present"
  exit
fi

echo
echo "Clean disks and setup bcache... "
dd if=/dev/zero of=$ssddev bs=512 count=8
dd if=/dev/zero of=$hdddev bs=512 count=8
wipefs -a $ssddev
wipefs -a $hdddev
apt-get update
apt-get install -y bcache-tools
make-bcache -C $ssddev -B $hdddev --writeback

echo
echo "Wait until device is ready... "
while [ ! -b /dev/bcache0 ]; do sleep 1; done

echo
echo "Config bcache device... "
echo $sequential_cutoff > /sys/block/bcache0/bcache/sequential_cutoff
echo "ACTION==\"add\", SUBSYSTEM==\"block\", ENV{MAJOR}==\"252\", ATTR{bcache/sequential_cutoff}=\"$sequential_cutoff\"" \
  > /etc/udev/rules.d/99-bcache_sequential_cutoff.rules
udevadm test /sys/block/bcache0

echo
echo "Format and mount bcache device..."
mkfs.ext4 /dev/bcache0
mkdir $mountname
mount /dev/bcache0 $mountname
echo "/dev/bcache0 $mountname ext4 rw 0 0" >> /etc/fstab

echo
echo "Config default home directory for new users on bcache partition... "
echo "home path of exising users will not be moved automaticaly"
mkdir $mountname/home
echo "#" >> /etc/default/useradd
echo "# Modifications:" >> /etc/default/useradd
echo "HOME=$mountname/home" >> /etc/default/useradd

echo
echo "Setup successfully finished"