linux-kernel - Re: [Fwd: [patch] media video cx23888 driver: ported to new kfifo API]

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Date:	Fri, 18 Dec 2009 23:09:26 +0100
From:	Stefani Seibold <stefani@...bold.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Andy Walls <awalls@...ix.net>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [Fwd: [patch] media video cx23888 driver: ported to new kfifo
 API]

Am Freitag, den 18.12.2009, 14:00 -0800 schrieb Andrew Morton:
> On Fri, 18 Dec 2009 22:57:22 +0100
> Stefani Seibold <stefani@...bold.net> wrote:
> 
> > But kfifo_len() did not
> > requiere a lock in my opinion. It is save to use without a look. 
> 
> What do you mean by this?  Safe in general, or safe in this particular driver?
> 

Safe until you don't call kfifo_reset(). kfifo_reset() is evil, because
it it the only function which breaks the single read/writer concept. 

This function modifies the in and the out fifo counters. Thats why i
introduced the kfifo_reset_out() function, which set the out to the
value of in, which means the fifo is empty. This function can be call
from the receiver of a fifo without locking.  

Stefani




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