systemd-nspawn replacement [containers/build#162]

systemd-nspawn

#!/usr/bin/env bash

## this is a total hack.  acbuild needs systemd-nspawn.  initially, I tried
## running the go agent in a rkt container, but failed for reasons I forget
## right now (overlayfs problems?).  then I ran into more problems with systemd-
## nspawn on CentOS 7.1, and I forget the origin.  we're getting closer: in
## CentOS 7.2 I'm able to run acbuild as root outside of a container.  but when
## running within the go agent, systemd-nspawn is killed for no discernable
## reason.  so, we're back to faking out acbuild by providing this systemd-
## nspawn-alike.

## https://github.com/appc/acbuild/issues/162

set -e -u -o pipefail

export PATH=$PATH:/usr/sbin

# systemd-nspawn \
#     -D .acbuild/target \
#     --register=no \
#     --setenv PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin \
#     /usr/bin/yum install -y java-1.8.0-openjdk-headless.x86_64

declare acbuild_PATH="${PATH}"
declare rootfs

keep_parsing=1
while [ $keep_parsing -eq 1 ]; do
    case "${1}" in 
        ## -D .acbuild/target
        -D )
            rootfs="$( readlink -f -n "${2}" )"
            shift 2
            ;;
        
        ## --register=no
        --register=* )
            shift
            ;;
        
        ## --quiet
        --quiet )
            shift
            ;;
        
        ## --setenv PATH=…
        --setenv )
            acbuild_PATH="${2}"
            shift 2
            ;;

        * )
            keep_parsing=0
            ;;
        
    esac
done

cmd=( "$@" )

## centos7 has /bin as a symlink to /usr/bin; centos6 does not.  I *think* the
## canonical path for these is /bin…
chrooted_mount="/bin/mount"
chrooted_umount="/bin/umount"

function unmount() {
    EXIT=$?
    
    set +e
    rm -f "${rootfs}/etc/resolv.conf"
    chroot "${rootfs}" ${chrooted_umount} /tmp

    [ -d "${rootfs}/run" ] && chroot "${rootfs}" ${chrooted_umount} /run

    ## must be last!
    chroot "${rootfs}" ${chrooted_umount} /proc
    
    exit $EXIT
}

trap unmount EXIT

chroot "${rootfs}" ${chrooted_mount} -t proc proc /proc

if [ -e "${rootfs}/run" ]; then
    chroot "${rootfs}" ${chrooted_mount} -t tmpfs tmpfs /run
fi

chroot "${rootfs}" ${chrooted_mount} -t tmpfs tmpfs /tmp

cp /etc/resolv.conf "${rootfs}/etc/"

rc=0
/usr/bin/env "PATH=${acbuild_PATH}" /usr/sbin/chroot "${rootfs}" "${cmd[@]}" || rc=$?
if [ $rc -ne 0 ]; then
    echo "'${cmd[*]}' failed: ${rc}"
fi

exit $rc