#!/bin/sh

exitmsg () {
  echo $1
  exit 1;
}

[ "$#" -lt 3 ] && echo 'Usage: lvmmount VGNAME VOLNAME PARTNUM [LOOPDEVICE]' && exit 2
VG=$1
vgs -qq $VG > /dev/null 2>&1 || exitmsg "The specified VG ($VG) does not exist"

VOL=$2
lvs -qq $VG/$VOL > /dev/null 2>&1 || exitmsg "The specified volume ($VOL) does not exist"

PART=$3
echo $PART | grep -qE "^[[:digit:]]+$" || exitmsg "The specified partition ($PART) must be a number"

DST=${4:-/dev/loop0}

losetup -P $DST /dev/$VG/$VOL || exitmsg "$DST is already used, specify another loop device (or deactivate it with losetup -D $DST"
if [ ! -e ${DST}p${PART} ]
then
  losetup -D $DST
  exitmsg "The is no partition ${PART} in ${VG}/{$VOL}"
fi

DSTDIR=/tmp/${VG}_${VOL}_${PART}
[ -e $DSTDIR ] && exitmsg "The $DSTDIR directory already exists, please check what you are doing"

mkdir -p $DSTDIR
mount ${DST}p${PART} ${DSTDIR}
echo "Mounted /dev/${VG}/${VOL} part ${PART} in ${DSTDIR}"
exit 0