#!/bin/sh
#
# Helper script to run an nbd client and mount its device to the given
# mount point. This script is invoked by "mount" with
# $1 = source (here it's an nbd URL like nbd://server/export
# $2 = mount point
# $3 = -o
# $4 = mount options
#
# The script starts a nbdfuse service client before mounting, and
# spawns a cleanup daemon that uses inotify to "discover" unmount to
# terminate the service client.

# Use an /run directory mangled from the source URL as "device node"
ADM="/run/$(echo -n "$1" | tr -c "[[:alnum:]-]" "_")"
if grep -qF " $ADM "  /proc/mounts ; then
    echo "*** $1 is already mounted" >&2
    exit 1
fi
mkdir -p $ADM

# Split up options between partition and loop options
POPTS=""
LOPTS=""
for X in $(echo $4 | tr , ' ') ; do
    case $X in
	kernel_cache|allow_other) POPTS="$POPTS -o $X" ;;
	*) LOPTS="$LOPTS,$X" ;;
    esac
done

# Set up the device node service
modprobe fuse || exit 1
nohup nbdfuse -C 1 $POPTS $ADM "$1" > /dev/null 2>&1 &

sleep 0.2
for i in 1 2 3 4 5 6 7 8 9 ; do
    # Loop-mount the nbdfuse "device" and spawn a cleanup daemon
    if mount -oloop,$LOPTS $ADM/nbd "$2" 2> /dev/null ; then
	# Spawn a process to umount $ADM when "$2" is umount-ed
	( (
	    inotifywait -e delete_self "$2" > /dev/null 2>&1
	    sleep 0.2
	    for i in 1 2 3 4 ; do
		umount $ADM 2> /dev/null && exit 0
		sleep 0.2
	    done
	) & ) &
	exit 0
    fi
    sleep 0.2
done

# Coming here if something wrong
umount $ADM