netdev - Re: [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface.

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Message-ID: <20080419163322.GA17089@2ka.mipt.ru>
Date:	Sat, 19 Apr 2008 20:33:22 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	netdev@...r.kernel.org, Max Krasnyansky <maxk@...lcomm.com>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] /dev/vring: simple userspace-kernel ringbuffer interface.

On Sun, Apr 20, 2008 at 02:05:31AM +1000, Rusty Russell (rusty@...tcorp.com.au) wrote:
> > Should this whole function and vring_used_buffer() be protected with
> > vr->lock mutex?
> 
> No; it's up to the caller to make sure that they are serialized.  In the case 
> of tun that happens naturally.
> 
> There are two reasons not to grab the lock.  It turns out that if we tried to 
> lock here, we'd deadlock, since the callbacks are called under the lock.  
> Secondly, it's possible to implement an atomic vring_used_buffer variant, 
> which could fail: this would avoid using the thread most of the time.

Yep, I decided that too. But it limits its usage to tun only or any
other system where only single thread picks up results, so no generic
userspace ring buffers?

-- 
	Evgeniy Polyakov
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