#!/bin/sh
# invoked by backup scripts as
#    lvm snap $vardir $device $mountpoint
#		creates and mounts on $vardir/snap-mount
#		creates $vardir/snap-device -> device
#    lvm drop $vardir

set -e

nargs=$#
opmode="$1"
vardir="$2"
device="$3"
mountpoint="$4"

lvm_lv=chiark-backup
lvm_lvtools_opts='-A n'
lvm_lvcreate_opts=
lvm_lvcreate_args=

test ! -f /etc/chiark-backup/settings.sh || . /etc/chiark-backup/settings.sh

case "$nargs.$opmode" in
4.snap|2.drop)
	;;
*)
	cat >&2 <<'END'
usage: .../lvm snap VARDIR DEV MOUNT
       .../lvm drop VARDIR
END
	exit 1
	;;
esac


#---------- clean up anything

snmnt="$vardir/snap-mount"
umount -v "$snmnt" || true
test ! -d "$snmnt" || rmdir -- "$snmnt"

set +e
old_lv_dev="$(readlink $vardir/snap-device)"
rc=$?
set -e

if [ $rc = 0 ]; then
	set +e
	lvchange    $lvm_lvtools_opts -a n $old_lv_dev
	lvremove -f $lvm_lvtools_opts      $old_lv_dev
	set -e
	rm $vardir/snap-device
fi

if test "$opmode" = drop; then
	echo 'lvm snap dropped'
	exit 0
fi

#---------- create snapshot

fstype="$(mount | sed -n \
 "s,^$device on $mountpoint type \([a-z0-9][a-z0-9]*\) .*,-t \1 ,p")"

if [ -z "$lvm_lvsize_opts" ]; then
	df="$(df -k $device)"
	blocks="$(printf "%s" "$df" |  sed -n '2,$s,^/dev/[^ 	]*[ 	][ 	]*[0-9][0-9]*[ 	][ 	]*\([0-9][0-9]*\)[ 	].*,\1,p')"
	lvm_lvsize_opts="-L $blocks"K
fi

lvpath="$(dirname "$device")/$lvm_lv"

ln -s -- "$lvpath" "$vardir"/snap-device

sync
lvcreate -s \
	$lvm_lvtools_opts \
	$lvm_lvsize_opts \
	-n $lvm_lv \
	$lvm_lvcreate_opts "$device" $lvm_lvcreate_args

mkdir -- "$snmnt"
mount -v -r $fstype $lvm_mount_opts "$lvpath" "$snmnt"

echo 'lvm snap activated'