vmbus_chan_read_available
uint32_t readable = vmbus_chan_read_available(chan);
vmbus_chan_read_available(pcb->chan));
bytes_canread = vmbus_chan_read_available(pcb->chan);
bytes_canread = vmbus_chan_read_available(pcb->chan);
__func__, vmbus_chan_read_available(pcb->chan));
uint32_t vmbus_chan_read_available(struct vmbus_channel *chan);