VMBUS_IC_BRSIZE
sc->ic_buflen = VMBUS_IC_BRSIZE;
sc->ic_buf = malloc(VMBUS_IC_BRSIZE, M_DEVBUF, M_WAITOK | M_ZERO);
error = vmbus_chan_open(chan, VMBUS_IC_BRSIZE, VMBUS_IC_BRSIZE, NULL, 0,
CTASSERT(VMBUS_IC_NEGOSZ < VMBUS_IC_BRSIZE);