1. make a ISO image
cp /dev/cdrom path/ISOName.iso
cp /dev/cdrom path/ISOName.iso
2. mount a ISO image
2.1
mkdir /mnt/iso
mount -t iso9660 -o loop path/ISOName.iso /mnt/iso
or
2.2
rm /dev/dvd
ln /dev/loop7 /dev/dvd
/sbin/losetup /dev/loop7 /root/shilenthill.iso (Note: In some Linux system, you can just use "losetup" but not "/sbin/losetup")
mount /dev/dvd /media/cdrom (or mount -t iso9660 -o loop /dev/dvd /media/cdrom)
3. unmount the virtual CD/DVD
umount /media/cdrom
losetup -d /dev/loop7
4. change a CD/DVD
losetup /dev/loop7 path/isoName.iso
Thanks to: http://zhidao.baidu.com/question/10990458.html
and: http://www.itjj.net/tech/OS/Linux/2006-12-22/77216.html