linux-kernel - Re: How to avoid data copies in a driver ?

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Message-ID: <Pine.LNX.4.61.0805141716120.11052@chaos.analogic.com>
Date:	Wed, 14 May 2008 17:23:10 -0400
From:	"linux-os (Dick Johnson)" <linux-os@...logic.com>
To:	"Francis Moreau" <francis.moro@...il.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: Re: How to avoid data copies in a driver ?

On Wed, 14 May 2008, Francis Moreau wrote:

> Hello,
>
> I'd like to optimize my driver, which receives data through a fifo and gives
> them to a user space application. In turns this application moves this data
> into a file.
>
> To avoid several useless copies, I'd like the application to pass to
> the driver
> a file descriptor (?) to  the driver and then the driver can directly
> move the
> received data to that file.
>
> Could anybody give me some example of such scheme ?
>
> Thanks,
> -- 
> Francis
> --

You memory-map the data. Impliment mmap() in your driver.
You can also impliment poll()  { select() } so your
application knows when new data are available.

You cannot use a user-mode file-descriptor in the kernel.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.22.1 on an i686 machine (5588.29 BogoMips).
My book : http://www.AbominableFirebug.com/
_

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