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Date: Fri, 18 Nov 2011 16:27:29 -0700
From: Gerrit Renker <gerrit@erg.abdn.ac.uk>
To: Jinxin Zheng <jinxinzheng@gmail.com>
Cc: Hagen Paul Pfeifer <hagen@jauu.net>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org
Subject: Re: ipv4 udplite broken in >=linux-3.0 ?
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Jinxin, -
| On Fri, Nov 18, 2011 at 8:04 PM, Hagen Paul Pfeifer <hagen@jauu.net> wrote:
| > * Jinxin Zheng | 2011-11-18 12:09:25 [+0800]:
| >
| >>I don't know how to debug udplite. Can any one of you give me a tip on
| >>how to get more debug info, then I can do further test and provide
| >>with it?
| >
| > net-next works for me:
That is very likely the point. Between 2.6.39 and 3.0 UDP-Lite checksum coverage was
broken and got only recently fixed. The correct kernel version should have the 
commit shown below. Alternatively, you can check include/net/udplite.h, which
should mention "Slow-path" and "Fast-Path" computation. UDP-Litev6 still uses the
slow path, that is why it is not affected.
    

commit f36c23bb9f822904dacf83a329518d0a5fde7968
Author: Gerrit Renker <gerrit@erg.abdn.ac.uk>
Date:   Mon Oct 17 19:07:30 2011 -0400

    udplite: fast-path computation of checksum coverage
    
    Commit 903ab86d195cca295379699299c5fc10beba31c7 of 1 March this year ("udp: Add
    lockless transmit path") introduced a new fast TX path that broke the checksum
    coverage computation of UDP-lite, which so far depended on up->len (only set
    if the socket is locked and 0 in the fast path).
    
    Fixed by providing both fast- and slow-path computation of checksum coverage.
    The latter can be removed when UDP(-lite)v6 also uses a lockless transmit path.