source: soft/giet_vm/create_dmg

#!/bin/bash
# Author: Cesar FUGUET
# Date  : Novembre 2013

clusters=65536
sector_size=512
sectors_per_cluster=8
reserved_sectors=4096

# FAT32 SPEC: The first two clusters are not present in the data region but
# they are used in the computation of the FAT sectors
data_region_clusters=$clusters-2

let "data_sectors = data_region_clusters * sectors_per_cluster"
let "fat_sectors  = (clusters * 4) / 512"

# The disk image contains:
#   - MBR sector : this sector is removed by this script as it will be copied
#                  after)
#   - Reserved region sectors (usually 32)
#   - FAT region sectors
#   - DATA region sectors
let "sectors      = data_sectors + fat_sectors + reserved_sectors + 1" 

platform=`uname`
echo "Detected platform: $platform"

if [[ $platform == "Darwin" ]]; then
        case $1 in
                create )
                        # Create disk image
                        # -fs        <fs>   : use filesystem <fs>
                        # -volname   <name> : use volume name <name>
                        # -srcfolder <src>  : copy every file in <src> into image
                        # -format    <fmt>  : format of image. UDRW (UDIF read/write image)
                        # -sectors   <sect> : size of image in 512-byte sectors
                        # -ov                           : overwrite existing image file
                        # -fargs         <args> : additional args to pass to newfs program 
                        #                            -F : FAT type (FAT32)
                        #                                -c : sector per cluster
                        #                                -n : number of FAT

                        if [[ -z $2 ]]; then
                                echo "Create action need second argument: <disk_image>"
                                exit 1;
                        fi;

                        # -F FAT type = 32 (FAT32)
                        # -c sectors/cluster
                        # -n number of FATs
                        # -r reserved sectors
                        # -k backup boot sector (VBR and FS INFO) = 0xffff (no backup)
                        echo "Creating empty disk image: $2.dmg"
                        fsargs="-F32 -c $sectors_per_cluster -n 1 -r $reserved_sectors -k 0xffff"

                        # -layout = NONE (No partition scheme. Hence no Master Boot Record)
                        hdiutil create \
                                -fs MS-DOS \
                                -volname virtualdisk \
                                -layout NONE \
                                -sectors $sectors \
                                -ov \
                                -fsargs "$fsargs" \
                                -type "UDIF" \
                                $2; 
                        ;;

                attach )
                        # Attach created disk image to the system and mount it
                        hdiutil attach $2
                        ;;

                detach )
                        # Detach attached device. Must pass as parameter the /dev/<device>
                        hdiutil detach $2
                        ;;

                info )
                        hdiutil imageinfo $2
                        ;;

                * )
                        echo "Pass the command as the first parameter: "
                        echo "  - create: create disk image"
                        echo "  - attach: attach created disk image to the system and "
                        echo "            mount it (arg: path to disk_image)"
                        echo "  - detach: detach specified device "
                        echo "            (arg: path to /dev/<device>)"
                        echo "  - info  : print information about created disk image"
                        echo "            (arg: path to disk_image)"
                        echo ""
                        echo "EXAMPLES:"
                        echo " ./create_diskimage.sh create disk_image"
                        echo " ./create_diskimage.sh attach /path/to/disk_image.dmg"
                        echo " ./create_diskimage.sh detach /dev/disk5"
                        echo " ./create_diskimage.sh info   /path/to/disk_image.dmg"
                        ;;
        esac;

elif [[ $platform == "Linux" ]]; then
        case $1 in
                create )

                        if [[ -z $2 ]]; then
                                echo "Create action need second argument: <disk_image>"
                                exit 1;
                        fi;

                        echo "Creating empty disk image: $2"
                        let "sectors = (sectors - 1) / 2" 

                        CREATE_DISK=$(command -v mkfs.vfat ||\
                                      command -v /sbin/mkfs.vfat ||\
                                      command -v /usr/sbin/mkfs.vfat ||\
                                      command -v /usr/local/sbin/mkfs.vfat)

                        if [ -z ${CREATE_DISK} ]; then
                                echo "error: command mkfs.vfat not found";
                                exit 1;
                        fi;

                        ${CREATE_DISK} \
                                -C \
                                -F32 \
                                -f 1 \
                                -R $reserved_sectors \
                                -S $sector_size \
                                -s $sectors_per_cluster \
                                -v \
                                $2.dmg $sectors
                        ;;

                * )
                        echo "Pass the command as the first parameter: "
                        echo "  - create: create disk image"
                        echo ""
                        echo "EXAMPLES:"
                        echo " ./create_diskimage.sh create disk_image"
                        ;;
        esac;

else
        echo "Your platform is not supported: $platform"
fi;