Add tools for mounting VHD as NBD from Linux

nbd-mount

@@ -0,0 +1,39 @@
+#!/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