linux-kernel - RE: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip

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Message-ID: <99B09243E1A5DA4898CDD8B70011144810830AB18B@EXMB04.eu.tieto.com>
Date:	Thu, 17 Mar 2011 15:38:07 +0200
From:	<Waldemar.Rymarkiewicz@...to.com>
To:	<arnd@...db.de>
CC:	<linux-i2c@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip

Arnd, 

>An application can open the device, and then do a 
>pthread_create() or a fork(). In either case, you have two 
>concurrent threads that have access to the file pointer and 
>can read from it concurrently, which is inherently racy 
>regarding which of the processes gets the data.

In that case I would relay on the application to synchronise the access.

>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.

>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.

Waldek--
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