freebsd jail config with host configuring things in guest (iface name, resolv.conf, etc)

jail.conf

path = "/jails/${name}";
vnet;
$iface = "$name";
vnet.interface = "${iface}b";
host.hostname = "$name";
exec.clean;
exec.start = "sh /etc/rc";
exec.stop = "sh /etc/rc.shutdown jail";
exec.release = "ifconfig ${iface}a destroy";
enforce_statfs = 1;
devfs_ruleset = 6;
allow.mount;
allow.mount.devfs;
mount.devfs;

porttest {
  exec.prepare += "~patmaddox/bin/jlprep $name $ip $iface";
  $ip = "192.168.2.5/24";
}

tf_snowflake {
  exec.prepare += "~patmaddox/bin/jlprep $name $ip $iface";
  $ip = "192.168.2.14/24";
}

jlprep.sh

#!/bin/sh
set -e

if [ ! "$1" -o ! "$2" -o ! "$3" ]; then
    echo "Usage: jlprep <name> <ip> <iface>"
    exit 1
fi

name=$1
ip=$2
iface=$3
jail="/jails/${name}"

## HOST - add interfaces
aname=`ifconfig epair create up`
bname=`echo "$aname" | sed -e 's/a$/b/'`

ifconfig jails addm $aname
ifconfig $aname name ${iface}a
ifconfig $bname name ${iface}b

## JAIL - configure rc.conf et al
ipprefix=`echo $ip | grep -o '^[[:digit:]]*.[[:digit:]]*.[[:digit:]]*'`
sysrc="sysrc -f ${jail}/etc/rc.conf"

$sysrc ifconfig_${iface}b_name="elink"
$sysrc ifconfig_elink="${ip}"
$sysrc defaultrouter="${ipprefix}.1"
$sysrc devfs_load_rulesets="YES"

mkdir -p ${jail}/usr/local/etc/pkg/repos
echo 'FreeBSD: { enabled: no }' > ${jail}/usr/local/etc/pkg/repos/FreeBSD.conf
echo 'poudriere: { url: "http://192.168.2.1", enabled: yes }' > ${jail}/usr/local/etc/pkg/repos/poudriere.conf

cat > ${jail}/etc/resolv.conf << EOF
nameserver 8.8.8.8
nameserver 8.8.4.4
EOF