#!/bin/bash
# readies a VHD device in Linux
# nbd-mount /path/to/vhd /dev/nbd0
APP_DIR="$(dirname "$0")"
NBD_FIND_FREE="$APP_DIR/nbd-find-free"
DRIVE="$1"
DISK_LABEL="$2"
DISK_PATH="/dev/disk/by-label/$DISK_LABEL"
SLEEP_INTERVAL=0.5

# find an empty nbd device
NBD_TARGET="$($NBD_FIND_FREE)"
if [ -z "$NBD_TARGET" ]; then
	echo "Cannot find free nbd device"
	exit 1
fi

# refuse to connect twice
EXISTING_DRIVE=$(pgrep -f "qemu-nbd.*$DRIVE")
if [ -n "$EXISTING_DRIVE" ]; then
	echo "$DRIVE already mounted" >&2
	exit 1
fi
EXISTING_NBD="$(pgrep -f "qemu-nbd.*$NBD_TARGET")"
if [ -n "$EXISTING_NBD" ]; then
	echo "$NBD_TARGET already mounted" >&2
	exit 1
fi


# wait for device to appear
if ! [ -e "$DISK_PATH" ]; then
	qemu-nbd --connect="$NBD_TARGET" "$DRIVE"

	# poll until the block device node appears or task times out
	until [ -L "$DISK_PATH" ] && [ -b "$DISK_PATH" ]; do
		sleep "$SLEEP_INTERVAL"
	done
fi