I'd strongly recommend the following:
1. For your immediate question, look at the "USB Gadget API":
2. To preserve your sanity and insure you have a reasonable chance
of success on this project, have your senior allocate some funds from
petty cash and start a project library that contains EACH of these books:
a) Linux Device Drivers, 3rd Ed
b) Linux Kernel Development, 2nd Ed
c) Building Embedded Systems with Linux
Even if you don't actually have to write any device drivers (and
I'm optimistic this might indeed be the case), these books
will give you INDISPENSABLE knowledge and insight you're going
to need. They'll pay for themselves almost immediately.
Please make sure your team gets them.
'Hope that helps .. PSM