vmbus_bufring
buflen = roundup(buflen, PAGE_SIZE) + sizeof(struct vmbus_bufring);
ch->ch_wrd.rd_ring = (struct vmbus_bufring *)ch->ch_ring;
ch->ch_wrd.rd_dsize = buflen - sizeof(struct vmbus_bufring);
ch->ch_rrd.rd_ring = (struct vmbus_bufring *)((uint8_t *)ch->ch_ring +
ch->ch_rrd.rd_dsize = buflen - sizeof(struct vmbus_bufring);
struct vmbus_bufring *rd_ring;