mount a qcow2 image in the host

sudo modprobe nbd max_part=8
sudo qemu-nbd -c /dev/nbd0 disk.qcow2
partx -a /dev/nbd0
fdisk -l /dev/nbd0
mount  /dev/nbd0p1 /mnt/xxx
...
umount dev/nbd0p1 
partx -d /dev/nbd0
qemu-nbd -d /dev/nbd0
rmmod nbd
killall qemu-nbd

mount iso image

mount -o loop /path/ti/file /mnt/usb   pas testé