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soc:2010:cooldavid:journal:week9 [2010/07/20 00:06]
cooldavid
soc:2010:cooldavid:journal:week9 [2010/07/26 05:43]
cooldavid
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   * We can now safely modify the heap_size as we want. :)   * We can now safely modify the heap_size as we want. :)
  
 +=== Michael'​s reply of my recent patchset ===
 +<​file>​
 +Thank you for your TCP patches, some of which I have applied directly to iPXE,
 +some of which have inspired me to make my own improvements. ​ I have not been
 +commenting on your patches, but I have carefully reviewed every version of
 +your patch set, picked out those that I want to apply or rework, and
 +maintained a list of those that are not yet integrated into iPXE.  At this
 +point, I'm down to a list of three patches:
 +
 +[tcp] Receive and Close flow adjustment
 +
 +This is difficult to apply following the changes to support out-of-order
 +packets, and I'm not sure how valuable it is.  Since commit 9ff8229 ("​[tcp]
 +Update received sequence number before delivering received data"​),​ which fixes
 +a problem that you identified (thank you!), I think that the TCP state is
 +consistent at the time the data is delivered to the upper layer, so any
 +actions it might take are safe.
 +
 +[tcp] Fix possible misjudged SYN/FIN ACKed status
 +
 +I believe this is unnecessary;​ I'm pretty sure that iPXE will never send SYN
 +or FIN in a packet that also contains data.  Therefore, if new data is ACKed
 +while we are sending one of these flags, it must be ACKing these flags. ​ Have
 +you found a way in which it is possible for us to send both SYN/FIN and data
 +at the same time?
 +
 +[tcp] Distinguish passive and active close with proper actions
 +
 +This one I have not yet reviewed thoroughly, though I am expecting that it
 +will be applied in some form.
 +
 +I am sorry that you have been disheartened by the lack of comments and
 +feedback on the gPXE mailing list.  I tend to avoid commenting on the gPXE
 +lists, because I do not find them to be a welcoming environment any more.
 +
 +Michael
 +</​file>​
 +
 +<​file>​
 +On Thursday 22 Jul 2010 11:09:23 Michael Brown wrote:
 +> [tcp] Receive and Close flow adjustment
 +
 +> This is difficult to apply following the changes to support out-of-order
 +> packets, and I'm not sure how valuable it is.  Since commit 9ff8229 ("​[tcp]
 +> Update received sequence number before delivering received data"​),​ which
 +> fixes a problem that you identified (thank you!), I think that the TCP
 +> state is consistent at the time the data is delivered to the upper layer,
 +> so any actions it might take are safe.
 +
 +Ignore that; I've just worked out that this patch makes perfect sense *if* we
 +also distinguish between passive and active close, and I see how it can be
 +implemented cleanly on top of the recent out-of-order changes.
 +
 +tcp_rx_data() should add the I/O buffer to a list rather than delivering it via
 +xfer_deliver_iob(). ​ tcp_rx_fin() should not call tcp_close().
 +tcp_process_rx_queue() should be adjusted to do something like:
 +
 +  struct list_head received = LIST_HEAD_INIT ( received );
 +  ...
 +  while ( ! list_empty ( &​tcp->​rx_queue ) ) {
 +     ...
 +     ​tcp_rx_data ( tcp, seq, iob_disown ( iobuf ), &​received );
 +     ...
 +  }
 +
 +  list_for_each_entry_safe ( iobuf, tmp, &​received,​ list ) {
 +    // deliver iobuf via xfer_deliver_iob()
 +  }
 +
 +  if ( tcp->​state & TCP_STATE_RCVD ( TCP_FIN ) )
 +    tcp_close ( tcp, 0 );
 +
 +I think that would handle everything sensibly, and would mean that we could
 +properly handle passive close since, in the case of a received data+FIN packet
 +that will also cause our higher layer protocol (e.g. http.c) to close the
 +connection, tcp_rx_fin() would see the FIN before http.c called xfer_close().
 +
 +Does this seem correct to you?  If so, would you like to put together a patch?
 +
 +Michael
 +</​file>​

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