netdev - question about tcp_ack_update

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Message-ID: <204986780909162024s785004e3q319f1b85c68f66@mail.gmail.com>
Date:	Thu, 17 Sep 2009 11:24:03 +0800
From:	hong liu <hong.liu96@...il.com>
To:	netdev@...r.kernel.org
Subject: question about tcp_ack_update_window

Hi,

In tcp_ack_update_window, we don't scale the window if it's a SYN packet.
This modification is introduced by Kevin Lahey during 2.5.75
(http://oss.sgi.com/archives/netdev/2003-10/msg01391.html).

tcp_ack_update_window is only called by tcp_ack, which is called by
tcp_rcv_synsent_state_process & tcp_rcv_established, and we change the
snd_wnd back to th->window in tcp_rcv_synsent_state_process, so why we
still need this  check in tcp_ack_update_window?

I think we may need to add tp->max_window = tp->snd_wnd in
tcp_rcv_syssent_state_process if we remove the check in tcp_ack_update_window.

The only problem I can see is: client entered into established state and sent
an ack (the last packet in 3-way handershake) to the server, but the packet
got lost / arrived slightly late. Then server resent a SYN+ACK packet,
then client can get a SYN packet and call tcp_ack in tcp_rcv_established.

Is this the only concern?

Thanks,
Hong
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