#!/bin/bash
# simh-wrapper --- wrapper around simh

# Author: Noah Friedman <friedman@splode.com>
# Created: 2010-10-09
# Public domain.

# $Id: simh-wrapper,v 1.1 2012/05/31 05:30:54 friedman Exp $

# Commentary:

# To use this, create a simh command script `simh.<name>.in' in the same
# directory with its virtual disks, and in that file add a comment of the
# form:
#
#	;; simh=pdp11
#
# (substitute whatever the appropriate binary is for your emulated system)
#
# The binary will be searched in ../bin relative to the simh.in file as
# well as the rest of your PATH list.

# This script sets up network interfaces for your guest using linux's iproute2
# As follows:
#
#	(vm) <-> if_guest <-> if_host <-> if_bridge
#
# The vm communicates with the host, and the outside world, via the bridge
# interface.  The bridge interface should exist and be up already.  The
# if_guest/host interfaces are created and torn down when the vm starts and
# exits.
#
# In addition to bridging, this script requires a linux kernel which
# supports "veth" ethernet tunnels (see iproute2 documentation and linux
# drivers/net/veth.c source).  This removes the need to create multiple
# tap/tun interfaces and then run a userspace program to shuttle packets
# between them.

# If you have no bridge interface set up already, make sure you have brctl
# (from the bridge-utils distribution) installed.  On Fedora/RedHat/CentOS,
# you can create a file in /etc/sysconfig/network-scripts/ifcfg-simhbr0 with:
#
#	DEVICE=simhbr0
#	TYPE=Bridge
#	IPADDR=192.168.111.1
#	NETMASK=255.255.255.0
#
# And then bring it up with "ifup simhbr0".

# Code:

setup()
{
    progname=${0##*/}

    progdir=${0%/*}
    case $progdir in $0 ) progdir=. ;; esac

    if [ -z "$1" ]; then
        find_simh_conf . "$progdir"
    elif [ -d "$1" ]; then
        find_simh_conf "$1"
    elif [ -f "$1" ]; then
        case $1 in
            *simh.*.in )
                topdir=${1%/*}
                case $topdir in $1 ) topdir=. ;; esac
                vmname=${1##*simh.}
                vmname=${vmname%.in}
                vmfile_in=$topdir/simh.$vmname.in ;;
            * )
                topdir=${1%/*}
                vmname=${1##*/}
                vmfile_in=$1 ;;
        esac
    else
        fatal "$1: File not readable or does not exist"
    fi
    verbose "Using $vmname simh configuration in $topdir"

    vmfile_tmp=${TMPDIR-/tmp}/simh.$vmname.$$

    find_bridge
    verbose "Using $bridge for ethernet bridge"
    veth0=${vmname}_host
    veth1=${vmname}_guest

    simh=`sed -ne '/;.*[ 	]simh=\([a-z0-9]*\)/{s//\1/p;q;}' "$vmfile_in"`
    case $simh in
        '' ) fatal "$vmname: don't know which simh binary to use" ;;
    esac
    PATH=$topdir/../bin:$PATH

    for prog in $simh simh-$simh; do
        if type -P $prog > /dev/null; then
            simh=`type -P $prog`
            break
        fi
    done
    verbose "Using $simh executable"

    uid=${UID-`id -u`}

    # simh passes local time to guest which infers it is UTC;
    # so tell simh that local time is in fact UTC.
    TZ=UTC
    export TZ
}

find_simh_conf()
{
    for dir in "$@"; do
        if find_vmname "$dir"; then
            topdir=$dir
            return 0;
        fi
    done
    fatal "cannot find any simh config file (simh.*.in)"
}

find_vmname()
{
    for f in "$1"/simh.*.in; do
        test -f "$f" || continue
        vmfile_in=$f
        vmname=${f#$1/simh.}
        vmname=${vmname%.in}
        return 0
    done
    return 1
}

find_bridge()
{
    for br in $SIMH_BRIDGE simhbr0 qemu0 ; do
        if [ -f /sys/class/net/$br/bridge/bridge_id ]; then
            bridge=$br
            return 0
        fi
    done

    for br in /sys/class/net/*/bridge/bridge_id; do
        bridge=${br#/sys/class/net/}
        bridge=${bridge%%/*}
        return 0
    done

    fatal "cannot find any ethernet bridge interface"
}

check_simh_netcap()
{
    case $uid in 0 ) return ;; esac

    test -x "$simh" || return;

    if ! getcap "$simh" | grep -q cap_net_raw.ep; then
        sudo setcap cap_net_raw+ep "$simh"
    fi
}

net_setup()
{
    bridge=$1 veth0=$2 veth1=$3

    if ! [ -f /sys/class/net/$bridge/bridge/bridge_id ]; then
      echo "${0##*/}: $bridge: ethernet bridge interface missing.  Aborting." 1>&2
      exit 1
    elif [ -d /sys/class/net/$veth0 ]; then
      echo "${0##*/}: $veth0: ethernet interface already exists.  Aborting." 1>&2
      exit 1
    fi

    ip link add $veth0 type veth peer name $veth1
    brctl addif $bridge $veth0

    ip link set $veth0 up
    ip link set $veth1 up
}

net_teardown()
{
    veth0=$1 veth1=$2

    # $veth0 will be removed from the bridge automatically.
    ip link del $veth0 type veth peer name $veth1
}

asroot()
{
    uid=${uid-${UID-`id -u`}}

    fn=$1
    shift

    case $uid in
        0 ) $fn "$@" ;;
        * ) sudo "$0" __$fn "$@" ;;
    esac
}

start()
{
    asroot net_setup $bridge $veth0 $veth1 || exit $?
    sed "s/\$TUNDEV/$veth1/" "$vmfile_in" > "$vmfile_tmp"
    (cd $topdir
     exec "$simh" "$vmfile_tmp" "$@"
    )
    exitstat=$?
}

stop()
{
    exitstat=${exitstat-$?}
    rm -f "$vmfile_tmp"
    asroot net_teardown $veth0 $veth1
    trap '' 1 2 3 15
    return $exitstat
}

fatal()
{
    echo "${0##*/}: $*" 1>&2
    exit 1
}

verbose()
{
    case ${SIMH_VERBOSE+t} in
        t ) echo "${0##*/}: $*" ;;
    esac
}

main()
{
    case $1 in
        '' ) : ;;
        __net_setup | __net_teardown ) fn=${1#__}; shift ; $fn "$@" ; exit $? ;;
        * ) conf=$1 ; shift ;;
    esac

    setup $conf
    check_simh_netcap
    trap 'stop; exit $exitstat' 1 2 3 15
    start "$@"
    stop
}

main "$@"

# eof