READ_REQ_SIZE
memset(gspca_dev->usb_buf, 0, READ_REQ_SIZE);
#define MAX_MODES ((READ_REQ_SIZE - 6) / 4)
if (USB_BUF_SZ < READ_REQ_SIZE) {
0, 0, gspca_dev->usb_buf, READ_REQ_SIZE, 1000);