# mount_once is used to only mount a given mountpoint once.
# If the given folder is already mounted, this won't do anything,
# even if the underlying filesystem is different.
# The first parameter is the filesystem to mount, the second parameter is the mountpoint.
#
# example: mount_once "/dev" "/chroot/chromeos/dev"

if ! mount | grep -q "\ $2\ " ; then
  mount -o bind $1 $2
fi