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    SubjectRe: select()/socket has problems under 2.2.x.
    On Sun, 7 Mar 1999, Andi Kleen wrote:

    >If the data is dropped it cannot be acked. Acking earlier data does not make
    >any sense, because the other end cannot do anything more than to retransmit,
    >and it should do that anyways even when we send no ack. What Alan said is that

    Yes. It was plain wrong to send duplicate acks because that way I was
    risking to start the fast-retransmit algorithm that suppose that acked
    data gets queued in the receiver.

    >Also disabling header prediction is not required (the user may eat the buffer backlog
    >and everything could be fine again when the next retransmit arrives)


    Index: tcp_input.c
    RCS file: /var/cvs/linux/net/ipv4/tcp_input.c,v
    retrieving revision
    diff -u -r1.1.2.23 tcp_input.c
    --- tcp_input.c 1999/03/07 20:00:23
    +++ tcp_input.c 1999/03/07 22:31:17
    @@ -65,9 +65,6 @@
    * to 3 * pmtu before going to
    * deadlocking. This will also improve
    * transfer throughput.
    - * Andrea Arcangeli: Always send back an ack even if we
    - * have to reject the incoming packet
    - * because our rcvbuf is full.

    #include <linux/config.h>
    @@ -1519,19 +1516,11 @@
    * shrink something if possible. -arca
    if (prune_queue(sk) < 0)
    - {
    * Bad: we aren't been able to shrink the out of
    - * order queue so we _must_ drop the packet. But
    - * we send an ack back to the other end so the
    - * sender will see our rcv_nxt. This way if the dropped
    - * packet was out of order the sender will be able
    - * to start fast retransmit. -arca
    + * order queue so we _must_ drop the packet.
    - tp->delayed_acks++;
    - tcp_enter_quickack_mode(tp);
    return 0;
    - }

    ret = tcp_data_queue(sk, skb);

    Andrea Arcangeli

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