overlay-boot/overlay-boot

#!/bin/sh
#
# This boot method runs a service subhost with a root filesystem that
# is an overlay of the subhost's root and an OS root. The service
# subhost is defined by a configuration file named on teh command line

OVERLAYDIR="$(realpath $(dirname $0))"

[ $(id -u) = 0 ] || exec sudo $0 $@
. $(dirname $(realpath $0))/functions $*

CONFIG="$1"
[ -r "$CONFIG" ] || die "Missing configuration $CONFIG"

config NAME $(basename $1 .${1##*.})
config LOG /tmp/oly-$NAME.log

if [ -z "$UNSHARED" ] ; then
    # Pre-unsharing:
    #
    # Create the network namespace for the subhost, then trigger
    # detached re-run with unshared mount namespace
    [ -r /run/netns/$NAME ] || {
	ip netns add $NAME
	ip netns exec $NAME ip link set lo up
    }
    exec env UNSHARED=yes unshare -m $0 $@ > $LOG 2>&1 &
    echo "Logging to $LOG" >&2
    exit 0
fi

config BASE
BASE="$(cd $(dirname $CONFIG); realpath $BASE)"

[ -z "$BASE" ] && die "BASE is unset; bogus $CONFIG ?"
[ -d "$BASE" ] || die "$BASE is not a directory; bogus $CONFIG ?"
cd "$BASE" || die "$BASE is inaccessible"

config LIVE "$BASE/live"
config UPPER "$BASE/root"
config WORK "$BASE/work"
config LOWER "/"
config CABLES ""
config START "networking ssh"
config SUBSHELL /bin/sh

# Setup virtual cabling
setup_veth_cables $NAME $CABLES

# Set up the mount for this subhost, including a new tmpfs on its /run
# and a default $UPPER/etc/network/interfaces if needed
echo setup_overlay "$NAME" "$LIVE" "$LOWER" "$UPPER" "$WORK"
setup_overlay "$NAME" "$LIVE" "$LOWER" "$UPPER" "$WORK"

exithandler() {
    ip netns del $NAME
    [ "$LOWER" != "$LIVE" ] && umount -R "$LIVE"
    [ -f "${UPPER%% *}" ] && [ -x "${UPPER%% *}" ] && \
	env ACTION=teardown $UPPER
}
trap "exithandler" 0

CMD="unshare -fp --mount-proc ip netns exec $NAME chroot $LIVE /bin/sh"
echo "$CMD"

config RAM_SIZE 50M

cat <<EOF | $CMD
set -x
mount -t proc proc /proc
mount -t devpts devpts /dev/pts
mount -t sysfs sysfs /sys
if [ "$RAM_SIZE" != "none" ] && ! grep -q '/run tmpfs' /proc/mounts ; then
    mount -t tmpfs -osize=$RAM_SIZE,mode=755 tmpfs /run
fi
for srv in $START ; do service \$srv start ; done
dummy_service() {
    [ \$# -gt 3 ] && return 0
    echo "Starting dummy service" >&2
    set +x
    [ -p /run/dummy_service ] || mkfifo /run/dummy_service
    ( printf dummy_service > /proc/self/comm ; read X < /run/dummy_service ) &
    set -x
}
dummy_service /proc/*/comm
exec /.reaper $NAME
EOF
echo "EXITED $CMD"