ring_tail
#define ring_posted(ring) (ring_head(ring) - ring_tail(ring))
ring_tail(ssk->rx_ring) >= ssk->recv_request_head &&
ssk->recv_request_head = ring_tail(ssk->rx_ring);
if (unlikely(id != ring_tail(ssk->rx_ring))) {
id, ring_tail(ssk->rx_ring));
mb = sdp_recv_completion(ssk, ring_tail(ssk->rx_ring));
WARN_ON(ring_head(ssk->rx_ring) != ring_tail(ssk->rx_ring));
if (unlikely(mseq != ring_tail(*tx_ring))) {
mseq, ring_tail(*tx_ring));
ring_head(ssk->tx_ring), ring_tail(ssk->tx_ring));
mb = sdp_send_completion(ssk, ring_tail(ssk->tx_ring));
WARN_ON(ring_head(ssk->tx_ring) != ring_tail(ssk->tx_ring));