[Discuss-gnuradio] A function named "usb_control_msg"

Dear everyone:

      You see in usrp_basic.h there is a function named _write_9862() and it uses function usrp_9862_write(),defined in usrp_prims_common.h. And usrp_9862_write() uses function usrp_spi_write(), also defined in usrp_prims_common.h.

usrp_spi_write() uses function write_cmd(), defined in usrp_prims_libusb0.c and usrp_prims_libusb1.c.

     In usrp_prims_libusb0.c write_cmd() uses a function named usb_control_msg(). But I can not find where usb_control_msg() is. Can anyone tell me where it is???