#!/bin/sh

# simple script for removing old zfs snapshots automatically (call me with cron, e.g. daily)
# caution, this is made with FreeBSD's `date', won't work with linux's and other OSes `date's...
# rev 1.13 lopez@yellowspace.net 17.03.2013

# abstract:
# given pool $POOL, destroy as many old snapshots as necessary to keep MINSPACE space free,
# but do not destroy anything younger than KEEPTIME days old (KEEPTIME has prio over MINSPACE).
# the two values will have to be tuned over time, usually you will 
# decrease MINSPACE and/or KEEPTIME as data grows...

# known issues:
# not really an issue, but right now this script is dataset agnostic, that is, it will sort 
# the snapshots by date asc, no matter in which dataset they are. more fine grained tuning 
# (with different retention policies for different datasets) could be implemented easilly..

# Specify the following variables in separate zfs_housekeeping.inc.sh (kept in same dir):

# MINSPACE=4398046511104 # in BYTES (4T)
# KEEPTIME=60 # in days
# POOL="tank" # pool name

HERE=$(/usr/bin/dirname "$0")

. "$HERE/zfs_housekeeping.inc.sh" 

if [ -z "$MINSPACE" -o -z "$KEEPTIME" -o -z "$POOL" ] ; then
	echo "Missing MINSPACE or KEEPTIME or POOL - zfs_housekeeping.inc.sh not found?"
	exit 1
fi

bcmp() {
        [ `echo "$1 $2 $3" | /usr/bin/bc` = "1" ]
}

giveStamp() {
        /bin/date -j -f "%a %b %d %T %Z %Y" "$1" "+%s"
}

one_destroyed() {
        touch "/tmp/zfs_housekeeper.$1"
}

did_destroy() {
        if [ -f "/tmp/zfs_housekeeper.$1" ] ; then
                d=1
                /bin/rm "/tmp/zfs_housekeeper.$1"
        else
                d=0
        fi
        [ "$d" = "1" ]
}

removeSnap() {
        if [ "$3" = "1" ] ; then echo "Removing $1, it is old, made on $2"; fi
        snaponly=`echo "$1" | /usr/bin/egrep -c '@.+'`
        if [ $snaponly -gt 0 ] ; then
                echo -n "Destroying $1 snapshot..."
                if [ $ND -eq 0 ] ; then
                        /sbin/zfs destroy "$1"
                        echo " done"
                else 
                        echo " (dry)"
                fi
                removedsomething=1
        else
                echo "$1 is not a valid snapshot name, dont destroy your pool! *g*"
                exit 1
        fi
}

# pid
mypid=$$
destroyed=0

# nd mode?
ND=0
ZHKVV=0
if [ "$1" = "-n" ] ; then
        ND=1
        ZHKVV=1
        echo "dry-run!"
fi

# see how many bytes are available
availbytes=$(/sbin/zfs get -Hp avail "$POOL" |  awk '{print $3}')

if bcmp "$availbytes" ">" "$MINSPACE"  ; then
        if [ "$ZHKVV" -gt 0 ] ; then echo "$availbytes B available, $MINSPACE B required, no need to delete"; fi
        exit 0
fi

# get the timestamp of the newest snapshot
# damned list verb does not accept a pool name with -t snapshot

lastsnapdate=$(/sbin/zfs list -t snapshot -H -o name,creation -s creation | \
        /usr/bin/egrep "^${POOL}" | \
        /usr/bin/cut -f 2 | \
        /usr/bin/tail -n 1)

lastsnapstamp=`giveStamp "$lastsnapdate"`

subtrsec=$((KEEPTIME*86400))
minstamp=$((lastsnapstamp-subtrsec))

export removedsomething=0
export MINSPACE
export POOL
export ZHKVV
export ND

/sbin/zfs list -t snapshot -H -o name,creation -s creation | /usr/bin/egrep "^${POOL}" | while IFS="	" read -r snapname snapdate ; do
        if [ "$ZHKVV" -gt 0 ] ; then echo "Name: $snapname, Date is $snapdate"; fi
        stamp=`giveStamp "$snapdate"`
        if bcmp "$stamp" "<" "$minstamp" ; then
                        nowavailbytes=$(/sbin/zfs get -Hp avail $POOL | awk '{print $3}')
        
                        if bcmp "$nowavailbytes" "<" "$MINSPACE" ; then
                                        removeSnap "$snapname" "$stamp" "$ZHKVV" 
                                        one_destroyed $mypid
                        fi
        fi
done

if did_destroy "$mypid" ; then
        echo "Destroyed enough snapshots"
else
        echo -n "WARNING: $0 did not find snapshots of $POOL older than $KEEPTIME days, "
        echo "yet available space is $availbytes, which is below $MINSPACE."
        exit 1
fi

exit 0