Mount/Read/Write Floppy Emulation USB sticks

fdemutool.bash

#!/usr/bin/env bash
# This is a tool to assist in the usage of floppy disk hardware emulators:
# https://en.wikipedia.org/wiki/Floppy_disk_hardware_emulator
#
# Several of these devices (presumably cheaper ones) don't store
# floppy drives as files on an existing file system, but rather just
# store the raw data with a 96K offset. It renders the USB-stick
# useless for any other purposes.
#
# It also means that you need customized software to access the virtual
# floppy disks. What a cheap way to do it!
#
# Anyhow, with the information provided on  Gough Lui's blogpost
# http://goughlui.com/2013/04/24/review-unbranded-1-44mb-usb-100-floppy-emulator/
#
# this script allows you to perform basic operations such as 
# - Create or Copy data to a virtual floppy disk
# - Write a floppy disk image to a specific slot (number)
# - Mount any virtual floppy disk image slot
#
# It only uses stock tools such as `dd`, `mkfs.msdos` and `mount`.
# Obtw, the mounting code needs loopback support in your kernel.
#
# By gammy

block_size=1024
block_count=1440
disk_padding=96

deps=(dd mount mkfs.msdos )
for dep in ${deps[@]}; do
        which $dep > /dev/null || exit $?
done

floppy_params="bs=${block_size} count=${block_count}"
let fs_limit="$block_size * $block_count"

function usage() {
	local me=$(basename $0)
	echo "Mount/Read/Write Floppy Emulation USB sticks"
	echo
	echo " - USE WITH EXTREME CAUTION - "
	echo
	echo "Usage: $me <mode> [in] [out] [slot]"
	echo
	echo "Modes:"
	echo "new  : Create an empty 1.44M disk image in [out]"
	echo "copy : Copy file or directory [in] to floppy image [out]"
	echo "       (runs 'new [out]' if [out] doesn't exist)"
	echo "write: Write [in (floppy image)] to [out (usb image)], slot [slot]"
	echo "dump : Write [in], [slot] to [out] *TODO*"
	echo "mount: Mount [in], [slot] to [out]"
	echo
	echo "Example:"
	echo "  $me copy ~/floppy_disk/ disk1.img"
	echo "  $me write disk1.img /dev/usb3 1"
	echo "  $me mount /dev/usb3 1 /mnt/fd"
	echo
	echo "For some interesting information, see"
	echo "http://goughlui.com/2013/04/24/review-unbranded-1-44mb-usb-100-floppy-emulator/"
}

function do_new() {
	local out="$1"

	if [ -z "$out" ]; then
		usage
		exit 1
	fi

	dd ${floppy_params} if=/dev/zero of="$out"
	mkfs.msdos "$out"

	if [ $? = 0 ]; then
		du -sk "$out"
	fi
}

function do_copy() {
	if [ "$UID" != "0" ]; then
		echo "Sorry, I need root priveleges to mount an image" >&2
		exit 1
	fi

	local in="$1"
	local out="$2"

	if [ -z "$in" -o -z "$out" ]; then
		usage
		exit 1
	fi

	if [ ! -e "$in" ]; then
		echo "\"$in\": doesn't exist" >&2
		exit 1
	fi

	srcsize=$(du -sk "$in" | cut -f 1)

	echo "Source size: ${srcsize}K"
	if [ $srcsize -ge $block_count ]; then
		echo -n "\"$in\": ${srcsize}K: "
		echo "won't fit onto \"$out\" ${block_count}" >&2
		exit 1
	fi

	if [ ! -e "$out" ]; then
		do_new "$out"
	else
		echo "Note: \"$out\": already exists"
	fi

	tmp_mount=$(mktemp --directory)
	mount "$out" "$tmp_mount" 

	ret=$?
	if [ "$ret" -ne 0 ]; then
		echo "mount \"$out\" \"$tmp_mount\": Failure: $ret" >&2
		exit $ret
	fi

	if [ -d "$in" ]; then
		cp -rv "$in/"* "$tmp_mount/"
	else
		cp -v "$in" "$tmp_mount/"
	fi	

	umount "$tmp_mount"
	rm -rf "$tmp_mount"
}

function do_write() {
	local in=$1
	local out=$2
	local slot=$3

	if [ -z "$in" -o -z "$out" -o -z "$slot" ]; then
		usage
		exit 1
	fi

	if [ ! -e "$in" ]; then
		echo "\"$in\": doesn't exist" >&2
		exit 1
	fi

	if [ -e "$out" ]; then
		echo "Note: \"$out\": already exists" >&2
	fi

	case "$slot" in
	    ''|*[!0-9]*) 
	    	echo "\"$slot\": Not a number" >&2
		exit 1
		;;
	    *) 
	    	;;
	esac

	let offset="(${block_count} + ${disk_padding}) * $slot"
	echo "Copy \"$in\" to \"$out\", slot $slot"
	echo dd ${floppy_params} seek="$offset" if="$in" of="$out"
	dd ${floppy_params} seek="$offset" if="$in" of="$out"
}

function do_mount() {
	if [ "$UID" != "0" ]; then
		echo "Sorry, I need root priveleges to mount an image" >&2
		exit 1
	fi

	local in=$1
	local out=$2
	local slot=$3

	if [ -z "$in" -o -z "$out" -o -z "$slot" ]; then
		usage
		exit 1
	fi

	if [ ! -e "$in" ]; then
		echo "\"$in\": doesn't exist" >&2
		exit 1
	fi

	case "$slot" in
	    ''|*[!0-9]*) 
	    	echo "\"$slot\": Not a number" >&2
		exit 1
		;;
	    *) 
	    	;;
	esac

	let offset="$block_size * ($block_count + $disk_padding) * $slot"
	echo mount -o loop,offset=${offset},sizelimit=${fs_limit} -t msdos "$in" "$out"

	mount -o loop,offset=${offset},sizelimit=${fs_limit} \
	      -t msdos \
	      "$in" \
	      "$out"

	ret="$?"

	if [ "$ret" = "32" ]; then
		echo -n "Failed to mount \"$in\", slot $slot. "
		echo "Does that slot exist?" >&2
		return $ret
	fi
}
mode=$1
shift

case "$mode" in
	"new")
		do_new "$1"
		;;
	"copy")
		do_copy "$1" "$2"
		;;
	"write")
		do_write  "$1" "$2" "$3"
		;;
	"mount")
		do_mount "$1" "$3" "$2"
		;;
	*)
		usage
		exit 1
esac

echo "Finished"