#!/bin/bash
# Thomas Kuschel - create btrfs snapshots
# 3.17: 2014-10-27
# switching to readable snapshots if kernel v3.17 -- 3.17.1 found
#set -e
# todo: to _not_ fire the bug, comment the following line:
TESTBUG="on"

VERSION="v3.17"
# Parse arguments:
SOURCE=$1
TARGET=$2
SNAP=$3
COUNT=$4
QUIET=$5
# where the btrfs is found (use command: which btrfs)
# BTRFS="/usr/bin/btrfs"
# BTRFS_ALT="/usr/local/bin/btrfs"
# Function to get path and right version:
vercomp() {
	if [[ $1 == $2 ]]
	then
		return 0
	fi
	local IFS=.
	local i ver1=($1) ver2=($2)
	# fill empty fields in ver1 with zeros
	for ((i=${#ver1[@]}; i<${#ver2[@]}; i++))
	do
		ver1[i]=0
	done
	for ((i=0; i<${#ver1[@]}; i++))
	do
		if [[ -z ${ver2[i]} ]]
		then
			# fill empty fields in ver2 with zeros
			ver2[i]=0
		fi
		if ((10#${ver1[i]} > 10#${ver2[i]}))
		then
			return 1
		fi
		if ((10#${ver1[i]} < 10#${ver2[i]}))
		then
			return 2
		fi
	done
	return 0
}

getpath() {
	scriptname=`/usr/bin/basename $0`
	path=`/usr/bin/which $scriptname`
	if [ -z "$path" ] ; then
		path="/usr/local/bin/"
		echo "Please install $scriptname to \"$path\""
		exit 10
	fi
	path="$path$scriptname"
	BTRFS=`/usr/bin/which btrfs`
	if [ -z "$BTRFS" ] ; then
		echo "btrfs is not installed."
		exit 11
	fi
}



# Function to display usage:
usage() {
	getpath
cat <<EOF
$scriptname: Take and rotate snapshots on a btrfs file system

usage: $scriptname [--version] source target snap_name count [-q]
  source:    path to make snaphost of
  target:    snapshot directory
  snap_name: Base name for snapshots, to be appended to
             date "+%F-%H%M"
  count:     Number of snapshots in the timestamp-@snap_name format to
             keep at one time for a given snap_name.
  [-q]:      Be quiet.
  --version: Print the version of this script,
             additionally the version of btrfs.

Example with systemd:
Please install the systemd files:
snapshot_home_daily.timer, snapshot_home_daily.service,...
to /etc/systemd/system
and enable the units with: systemctl enable snapshot_home_daily

Example for crontab:
15,30,45 * * * *  root $0 /home /snap quarterly 4 -q
0        * * * *  root $0 /home /snap hourly 8 -q

Example for anacrontab:
1        15 daily_snap   $0 /home /snap daily 8
7        17 weekly_snap  $0 /home /snap weekly 5
@monthly 19 monthly_snap $0 /home /snap monthly 3
EOF
 exit
}
getpath
# Basic argument checks:
if [ -n "$SOURCE" ] && [ "x$SOURCE" == "x--version" ] ; then
	# scriptname=`/usr/bin/basename $0`
	echo "$scriptname $VERSION"
	echo `$BTRFS --version`
	echo "Linux "`uname -r`
	exit
fi
if [ -z $COUNT ]  ; then
    usage
fi
if [ ! -z $6 ] ; then
    echo "Too many parameters."
    usage
fi
if [ -n "$QUIET" ] && [ "x$QUIET" != "x-q"  ] ; then
    echo "Parameter 4 is either -q or empty. Given: \"$QUIET\""
    usage
fi

# $max_snap is the highest number of snapshots that will be kept for $SNAP.
max_snap=$(($COUNT -1))

# Clean up older snapshots:
for i in `ls $TARGET|sort |grep @${SNAP}|head -n -${max_snap}`; do
	cmd="$BTRFS subvolume delete $TARGET/$i"
	if [ -z $QUIET ]; then
		echo $cmd
	fi
	$cmd >/dev/null
done

LINUXVERSION=`uname --kernel-release`
# echo vercomp $LINUXVERSION "3.17"
vercomp $LINUXVERSION "3.17"
case $? in
	0) READONLY="";;
	1) READONLY="";;
	2) READONLY="-r";;
esac
if [ -z $READONLY ]; then
	echo "Note: btrfs exceptionally creates a read-and-write snapshot with kernel version = 3.17.1"
	# give it a try for next version...
	vercomp $LINUXVERSION "3.17.2"
	case $? in
		0) READONLY="-r";;
		1) READONLY="-r";;
		2) READONLY="";;
	esac
fi
# overwrite explicitely the READONLY for testing:
if [ -n "$TESTBUG" ] && [ "$TESTBUG" == "on" ]; then
	echo "Warning: TESTBUG is set!"
	READONLY="-r"
fi
# Create new snapshot:
cmd="$BTRFS subvolume snapshot $READONLY $SOURCE $TARGET/`date "+%F-%H%M-@${SNAP}"`"
if [ -z $QUIET ]; then
	echo $cmd
fi
$cmd >/dev/null