From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip Date: Thu, 17 Mar 2011 14:54:42 +0100 Message-ID: <201103171454.42838.arnd@arndb.de> References: <1299766808-2535-1-git-send-email-waldemar.rymarkiewicz@tieto.com> <201103171407.58164.arnd@arndb.de> <99B09243E1A5DA4898CDD8B70011144810830AB18B@EXMB04.eu.tieto.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <99B09243E1A5DA4898CDD8B70011144810830AB18B-TzrFtyi11j7rLp5S7fUuNkEOCMrvLtNR@public.gmane.org> Sender: linux-i2c-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Waldemar.Rymarkiewicz-++hxYGjEMp0AvxtiuMwx3w@public.gmane.org Cc: linux-i2c-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-i2c@vger.kernel.org On Thursday 17 March 2011, Waldemar.Rymarkiewicz-++hxYGjEMp0AvxtiuMwx3w@public.gmane.org wrote: > >This is not very different from opening the file descriptor in > >multiple processes, which you prevent using your logic. > > but in the case when two independent applications try to open > my device I can't let the second to access. They obviously won't > synch the access. My point was that you don't need to worry. > >You can of course argue that you try your best to prevent the > >race. Traditionally, e.g. on serial ports and the like, we > >don't do this but instead rely on user space synchronizing the > >access. What you have to make sure of course is that multiple > >threads calling read on the same file can never bring the > >kernel driver into an invalid state. > > I assume, if an application shares the file pointer deliberately > it have to sync the access. In other cases, the driver needs to > secure it. As I said, it's not important if you do it and it certainly doesn't cause harm to prevent multiple open. It's just that generally we don't care too much about this problem. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751719Ab1CQNyr (ORCPT ); Thu, 17 Mar 2011 09:54:47 -0400 Received: from moutng.kundenserver.de ([212.227.17.9]:53851 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750779Ab1CQNyn (ORCPT ); Thu, 17 Mar 2011 09:54:43 -0400 From: Arnd Bergmann To: Waldemar.Rymarkiewicz@tieto.com Subject: Re: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip Date: Thu, 17 Mar 2011 14:54:42 +0100 User-Agent: KMail/1.12.2 (Linux/2.6.37; KDE/4.3.2; x86_64; ; ) Cc: linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org References: <1299766808-2535-1-git-send-email-waldemar.rymarkiewicz@tieto.com> <201103171407.58164.arnd@arndb.de> <99B09243E1A5DA4898CDD8B70011144810830AB18B@EXMB04.eu.tieto.com> In-Reply-To: <99B09243E1A5DA4898CDD8B70011144810830AB18B@EXMB04.eu.tieto.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201103171454.42838.arnd@arndb.de> X-Provags-ID: V02:K0:hInXbPfTG3ABeU/pnW8O+d++acuLekelfhSY3XFN1bp 9NfZMZKAAWIFJRPCu3NWxIOCTF3ULZXJMaC7Muwv+wBBKYilqd FR1YPF09Vh3OatmzOTdbeQ3qfe2dOv7ktjGqN9OqxovJ0jKIS1 x5sN2cky/aalIX/+aMsGK3mXQmrjSc3xUk8ExpUFx2cXk+1FWY voCIm36XL+6xO7wdNy/Fw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday 17 March 2011, Waldemar.Rymarkiewicz@tieto.com wrote: > >This is not very different from opening the file descriptor in > >multiple processes, which you prevent using your logic. > > but in the case when two independent applications try to open > my device I can't let the second to access. They obviously won't > synch the access. My point was that you don't need to worry. > >You can of course argue that you try your best to prevent the > >race. Traditionally, e.g. on serial ports and the like, we > >don't do this but instead rely on user space synchronizing the > >access. What you have to make sure of course is that multiple > >threads calling read on the same file can never bring the > >kernel driver into an invalid state. > > I assume, if an application shares the file pointer deliberately > it have to sync the access. In other cases, the driver needs to > secure it. As I said, it's not important if you do it and it certainly doesn't cause harm to prevent multiple open. It's just that generally we don't care too much about this problem. Arnd