usbio_i2c_rw
struct usbio_i2c_rw *wbuf = i2c->rwbuf;
#define I2C_RW_OVERHEAD (sizeof(struct usbio_bulk_packet) + sizeof(struct usbio_i2c_rw))
struct usbio_i2c_rw *rwbuf;
struct usbio_i2c_rw *rbuf = i2c->rwbuf;