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

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Message-ID: <482C2383.5070206@arndnet.de>
Date:	Thu, 15 May 2008 13:50:27 +0200
From:	Arnd Hannemann <arnd@...dnet.de>
To:	Francis Moreau <francis.moro@...il.com>
CC:	"linux-os (Dick Johnson)" <linux-os@...logic.com>,
	linux-kernel@...r.kernel.org
Subject: Re: How to avoid data copies in a driver ?

Francis Moreau wrote:
> Hello,
> 
> On Wed, May 14, 2008 at 11:23 PM, linux-os (Dick Johnson)
> <linux-os@...logic.com> wrote:
>> 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.
>>
> 
> Why not ?

http://kernelnewbies.org/FAQ/WhyWritingFilesFromKernelIsBad

> 
> I'm suprised because what I need doens't seem so uncommon, usually
> devices send or
> receive data to/from files. So a helper (system call ?) to achieve
> that other than the basic
> read/write seems needed, no ?

Usually devices send or receive just data, and they shouldn't care about
file format, filesystems, permissions and all this stuff...

Regards,
Arnd

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