netdev - Re: [PATCH net-next 0/6] kcm: Kernel Connection Multiplexor (KCM)

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Message-ID: <87y4dnfxl8.fsf@stressinduktion.org>
Date:	Tue, 24 Nov 2015 12:25:39 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	David Miller <davem@...emloft.net>, tom@...bertland.com
Cc:	netdev@...r.kernel.org, kernel-team@...com, davewatson@...com,
	alexei.starovoitov@...il.com
Subject: Re: [PATCH net-next 0/6] kcm: Kernel Connection Multiplexor (KCM)

Hello,

David Miller <davem@...emloft.net> writes:

> From: Tom Herbert <tom@...bertland.com>
> Date: Mon, 23 Nov 2015 09:33:44 -0800
>
>> The TCP PSH flag is not defined for message delineation (neither is
>> urgent pointer). We can't change that (many people have tried to add
>> message semantics to TCP protocol but have always failed miserably).
>
> Agreed.
>
> My only gripe with kcm right now is a lack of a native sendpage.
> We should be able to zero copy data through KCM streams without
> any problems whatsoever.

I understood from Tom's last mail that the messages are being
constructed *in kernel memory* before sending out of the tcp
socket. What advantage gives sendpage? The message construction must
actually happen before to fill in the necessary headers for the length,
so receiver can dissect again. Streaming semantics don't really fit
here?

Bye,
Hannes
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