netdev - Re: Fwd: Packet mmap: TX RING and zero copy

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Date:	Fri, 5 Sep 2008 15:55:14 +0200
From:	"Johann Baudy" <johaahn@...il.com>
To:	"Evgeniy Polyakov" <johnpol@....mipt.ru>
Cc:	netdev@...r.kernel.org
Subject: Re: Fwd: Packet mmap: TX RING and zero copy

Hi Evgeniy,

> That's a bug. Likely no one sends file content via udp, so it was not
> detected...

Ok, I'll will run a FTRACE of this issue on monday;

>> I will try to investigate it but for my app sendfile() is not
>> conceivable. Only vmsplice could, but too slow.
>
> Well, you can mmap empty file into the RAM, lock it there, DMA data from
> the sensor to the mmapped area, add headers (just in the mapped area)
> and then sendfile that file.. Single syscall, zero-copy, standard
> interfaces :)
>

OK but it seems that there is no way to control packet format.
(beginning of packet and size of packet).
Each packet must start with a specific header (on my app). This is a
kind of streaming.

Thanks,
Johann





-- 
Johann Baudy
johaahn@...il.com
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