Em Wed, Nov 28, 2007 at 08:35:10AM +0000, Gerrit Renker escreveu:
> [DCCP]: Integrate state transitions for passive-close
>
> This adds the necessary state transitions for the two forms of passive-close
>
> * PASSIVE_CLOSE - which is entered when a host receives a Close;
> * PASSIVE_CLOSEREQ - which is entered when a client receives a CloseReq.
>
> Here is a detailed account of what the patch does in each state.
>
> 1) Receiving CloseReq
> ----------------------
> The pseudo-code in 8.5 says:
>
> Step 13: Process CloseReq
> If P.type == CloseReq and S.state < CLOSEREQ,
> Generate Close
> S.state := CLOSING
> Set CLOSING timer.
>
> This means we need to address what to do in CLOSED, LISTEN, REQUEST, RESPOND, PARTOPEN, and OPEN.
>
> * CLOSED: silently ignore - it may be a late or duplicate CloseReq;
> * LISTEN/RESPOND: will not appear, since Step 7 is performed first (we know we are the client);
> * REQUEST: perform Step 13 directly (no need to enqueue packet);
> * OPEN/PARTOPEN: enter PASSIVE_CLOSEREQ so that the application has a chance to process unread data.
>
> When already in PASSIVE_CLOSEREQ, no second CloseReq is enqueued. In any other state, the CloseReq is ignored.
> I think that this offers some robustness against rare and pathological cases: e.g. a simultaneous close where
> the client sends a Close and the server a CloseReq. The client will then be retransmitting its Close until it
> gets the Reset, so ignoring the CloseReq while in state CLOSING is sane.
>
> 2) Receiving Close
> -------------------
> The code below from 8.5 is unconditional.
>
> Step 14: Process Close
> If P.type == Close,
> Generate Reset(Closed)
> Tear down connection
> Drop packet and return
>
> Thus we need to consider all states:
> * CLOSED: silently ignore, since this can happen when a retransmitted or late Close arrives;
> * LISTEN: dccp_rcv_state_process() will generate a Reset ("No Connection");
> * REQUEST: perform Step 14 directly (no need to enqueue packet);
> * RESPOND: dccp_check_req() will generate a Reset ("Packet Error") -- left it at that;
> * OPEN/PARTOPEN: enter PASSIVE_CLOSE so that application has a chance to process unread data;
> * CLOSEREQ: server performed active-close -- perform Step 14;
> * CLOSING: simultaneous-close: use a tie-breaker to avoid message ping-pong (see comment);
> * PASSIVE_CLOSEREQ: ignore - the peer has a bug (sending first a CloseReq and now a Close);
> * TIMEWAIT: packet is ignored.
>
> Note that the condition of receiving a packet in state CLOSED here is different from the condition "there
> is no socket for such a connection": the socket still exists, but its state indicates it is unusable.
>
> Last, dccp_finish_passive_close sets either DCCP_CLOSED or DCCP_CLOSING = TCP_CLOSING, so that
> sk_stream_wait_close() will wait for the final Reset (which will trigger CLOSING => CLOSED).
>
> Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
Applied
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