VAR-SOM-MX6 USB OTG as device
From Variscite Wiki
VAR-SOM-MX6 - USB OTG Device
Plug a cable to a A linux host.
Folow www.linux-usb.org/gadget/file_storage.html and build the backing_file.
On the Target:
$ modprobe g_mass_storage file=./backing_file
On the Host:
use dmesg and find out your device for example /dev/sdb $ sudo dd if=/dev/zero of=/dev/sdb bs=128k count=1000