#!/bin/bash
#
# Control program for bespoke arbitrary services through unshared sub-hosts
#
# $1 = the command: start or stop
# $2 = the sub-host to start or stop
# $3... = the optional chroot-ed command (/startup by default)

SCRIPT=$0
CMD=$1
NAME=$2
shift 2

usage() {
    echo "$SCRIPT (start|stop) <subhost>" >&2
    exit 1
}

[ -z "$NAME" ] && usage

: ${ATTIC=/opt/srv}
: ${BRIDGE=srv_br}
: ${TARGET=/srv/$NAME}
: ${LOWER=$ATTIC/daedalus.fs}
: ${IMAGE=$ATTIC/$NAME/$NAME.img}
: ${UPPER=$ATTIC/$NAME/root}
: ${WORK=$ATTIC/$NAME/work}
: ${MOUNT=$ATTIC/$NAME/mnt}
: ${NSNAME=$NAME}
: ${NETH=1}

create_subhost() {
    mkdir -p $TARGET $MOUNT $UPPER $WORK
}

setup_network() {
    if [ -n "$BRIDGE" ] ; then
	brctl show $BRIDGE >& /dev/null || brctl addbr $BRIDGE
    fi

    E=0
    ip netns add $NSNAME
    for I in $(eval echo "{1..$NETH}") ; do
	IF=$NAME$E
	ip link add $IF type veth peer name eth$E netns $NSNAME
	ip link set $IF up
	[ -n "$BRIDGE" ] && brctl addif $BRIDGE $IF
	E=$((E+1))
    done
}

setup_rootfs() {
    if [ -e "$IMAGE" ] ; then
	mount $IMAGE $MOUNT || exit 1
	LOWER=$MOUNT/root
	WORK=$MOUNT/work
    fi
    mount -t overlay $NAME -olowerdir=$LOWER,upperdir=$UPPER,workdir=$WORK \
	  $TARGET
}

case "$CMD" in
    start)
	cd "$ATTIC" || exit 1
	[ -e "/run/netns/$NSNAME" ] || setup_network
	[ -d "$MOUNT" ] || create_subhost
	grep -q "^$NAME $TARGET overlay" /proc/mounts || setup_rootfs
	START=/bin/bash
	[ -x $TARGET/startup ] && START=/startup
	exec ip netns exec $NSNAME unshare \
	     --fork --pid --mount-proc --kill-child \
	     --uts --ipc --mount --cgroup \
	     "--root=$TARGET" $START
	;;
    stop)
	umount $TARGET
	[ -e $IMAGE ] && umount $MOUNT
	ip netns del $NSNAME
	;;
    *)
	usage
	;;
esac