How the new TCP output machine [nyi] works. Data is kept on a single queue. The skb->users flag tells us if the frame is one that has been queued already. To add a frame we throw it on the end. Ack walks down the list from the start. We keep a set of control flags sk->tcp_pend_event TCP_PEND_ACK Ack needed TCP_ACK_NOW Needed now TCP_WINDOW Window update check TCP_WINZERO Zero probing sk->transmit_queue The transmission frame begin sk->transmit_new First new frame pointer sk->transmit_end Where to add frames sk->tcp_last_tx_ack Last ack seen sk->tcp_dup_ack Dup ack count for fast retransmit Frames are queued for output by tcp_write. We do our best to send the frames off immediately if possible, but otherwise queue and compute the body checksum in the copy. When a write is done we try to clear any pending events and piggy back them. If the window is full we queue full sized frames. On the firs timeout in zero window we split this. On a timer we walk the retransmit list to send any retransmits, update the backoff timers etc. A change of route table stamp causes a change of header and recompute. We add any new tcp level headers and refinish the checksum before sending.