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