#! /bin/sh -e

if ! [ -d "$1" ]; then
    echo "usage: $0 DIRECTORY"
    echo
    echo "Makes DIRECTORY a read/write tmpfs mount with the same"
    echo "contents."
    exit 1
fi

fsname=$(basename $1)
mkdir /tmp/$fsname
mount -t tmpfs $fsname /tmp/$fsname
(cd $1 && tar cf - .) | (cd /tmp/$fsname && tar xf -)
mount -o move /tmp/$fsname $1
rmdir /tmp/$fsname