| #!/bin/sh |
| # |
| # Perform a bind mount, copying existing files as we do so to ensure the |
| # overlaid path has the necessary content. |
| |
| if [ $# -lt 2 ]; then |
| echo >&2 "Usage: $0 spec mountpoint [OPTIONS]" |
| exit 1 |
| fi |
| |
| # e.g. /var/volatile/lib |
| spec=$1 |
| |
| # e.g. /var/lib |
| mountpoint=$2 |
| |
| if [ $# -gt 2 ]; then |
| options=$3 |
| else |
| options= |
| fi |
| |
| [ -n "$options" ] && options=",$options" |
| |
| mkdir -p "${spec%/*}" |
| |
| if [ -d "$mountpoint" ]; then |
| |
| if [ -d "$spec" ]; then |
| specdir_existed=yes |
| else |
| specdir_existed=no |
| mkdir "$spec" |
| fi |
| |
| # Fast version of calculating `dirname ${spec}`/.`basename ${spec}`-work |
| overlay_workdir="${spec%/*}/.${spec##*/}-work" |
| mkdir "${overlay_workdir}" |
| |
| # Try to mount using overlay, which is must faster than copying files. |
| # If that fails, fall back to slower copy. |
| if ! mount -t overlay overlay -olowerdir="$mountpoint",upperdir="$spec",workdir="$overlay_workdir" "$mountpoint" > /dev/null 2>&1; then |
| |
| if [ "$specdir_existed" != "yes" ]; then |
| cp -aPR "$mountpoint"/. "$spec/" |
| fi |
| |
| mount -o "bind$options" "$spec" "$mountpoint" |
| fi |
| elif [ -f "$mountpoint" ]; then |
| if [ ! -f "$spec" ]; then |
| cp -aP "$mountpoint" "$spec" |
| fi |
| |
| mount -o "bind$options" "$spec" "$mountpoint" |
| fi |