The Z8530 layer provides functions to queue packets for transmission. The driver internally buffers the frame currently being transmitted and one further frame (in order to keep back to back transmission running). Any further buffering is up to the caller.
The function z8530_queue_xmit takes a network buffer in sk_buff format and queues it for transmission. The caller must provide the entire packet with the exception of the bitstuffing and CRC. This is normally done by the caller via the syncppp interface layer. It returns 0 if the buffer has been queued and non zero values for queue full. If the function accepts the buffer it becomes property of the Z8530 layer and the caller should not free it.
The function z8530_get_stats returns a pointer to an internally maintained per interface statistics block. This provides most of the interface code needed to implement the network layer get_stats callback.