The Mass Storage Gadget acts as a USB Mass Storage disk drive.
As its storage repository it can use a regular file or a block
device (in much the same way as the "loop" device driver),
specified as a module parameter or sysfs option.

This is heavily based on File-backed Storage Gadget and in most
cases you will want to use FSG instead. This gadget is mostly
here to test the functionality of the Mass Storage Function
which may be used with composite framework.

Say "y" to link the driver statically, or "m" to build
a dynamically linked module called "g_file_storage". If unsure,
consider File-backed Storage Gadget.

source code:

drivers/usb/gadget/