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

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Message-ID: <38b2ab8a0805150508j5adc4755n8eb378b414b2dc03@mail.gmail.com>
Date:	Thu, 15 May 2008 14:08:39 +0200
From:	"Francis Moreau" <francis.moro@...il.com>
To:	"Arnd Hannemann" <arnd@...dnet.de>
Cc:	"linux-os (Dick Johnson)" <linux-os@...logic.com>,
	linux-kernel@...r.kernel.org
Subject: Re: How to avoid data copies in a driver ?

On Thu, May 15, 2008 at 1:50 PM, Arnd Hannemann <arnd@...dnet.de> wrote:
> 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
>

ok, relayfs might be what I need, thanks.

>>
>> 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...
>

The fact is that the data usually ends into a file.

thanks
-- 
Francis
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