CONFIG_USB_F_MASS_STORAGE (not configurable)

modulename: usb_f_mass_storage.ko

configname: CONFIG_USB_F_MASS_STORAGE

Linux Kernel Configuration
└─>Device Drivers
└─>USB support
└─>USB Gadget Support
└─>USB_F_MASS_STORAGE
In linux kernel since version 3.13 (release Date: 2014-01-19)  
source code:
drivers/usb/gadget/function//