#!/bin/sh
#

#	Toralf Förster
#	Hamburg
#	Germany

# set -x

while getopts r: opt
do
	case $opt in
	r)	UMLROOTFS=$OPTARG
		;;
	
	*)	echo "Usage : $(basename $0) -r <root fs>"
		exit 1
		;;
	esac
done


#############################################################################
#
if [[ ! -f $UMLROOTFS || ! -r $UMLROOTFS || ! -w $UMLROOTFS ]]; then
	echo "no r/w able root-fs $UMLROOTFS"
	exit 1
fi

#	we assume different file names for the images
#
NAME=$(basename $UMLROOTFS)

if [[ "$(whoami)" != "root" ]]; then
	echo " You must be root !"
	exit 2
fi

#	load module if neccessary and sleep a sec
#	to give it time for initialization
#
if [[ -z "$(lsmod | grep "^loop ")" ]]; then
	modprobe loop && sleep 2 || exit 3
fi

MNTPNT=/mnt/ramdisk/$NAME
if [[ ! -d $MNTPNT ]]; then
	mkdir $MNTPNT || exit 1
fi

#	is this UML image already in use ?
#
mountpoint -q $MNTPNT
if [[ $? -eq 0 ]]; then
	echo "$MNTPNT is already mounted"
	exit 5
fi

#	temp dir for emerging packages, the UML image itself doesn't have too much free disk space
#
TMPPORTAGE=/mnt/ramdisk/uml_portage_$NAME
if [[ ! -d $TMPPORTAGE ]]; then
	mkdir $TMPPORTAGE
	sudo chown portage:portage $TMPPORTAGE
fi


#############################################################################
#
mount -o loop	$UMLROOTFS		$MNTPNT
mount -t proc	none			$MNTPNT/proc
mount -o bind	/dev			$MNTPNT/dev
mount -o bind	/dev/pts		$MNTPNT/dev/pts
mount -o bind	/sys			$MNTPNT/sys
mount -o bind	/usr/portage		$MNTPNT/usr/portage
mount -o bind	/usr/local/portage	$MNTPNT/usr/local/portage
mount -o bind	$TMPPORTAGE		$MNTPNT/var/tmp/portage

chroot $MNTPNT /bin/bash -c "su -"
RC=$?

umount	$MNTPNT/var/tmp/portage
umount	$MNTPNT/usr/local/portage
umount	$MNTPNT/usr/portage
umount	$MNTPNT/sys
umount	$MNTPNT/dev/pts
umount	$MNTPNT/dev
umount	$MNTPNT/proc
umount	$MNTPNT

rmdir $TMPPORTAGE/._unmerge_/ 2>/dev/null
rmdir $TMPPORTAGE
rmdir $MNTPNT

exit $RC