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

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Message-Id: <200804200246.00282.rusty@rustcorp.com.au>
Date:	Sun, 20 Apr 2008 02:45:59 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
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 Sunday 20 April 2008 02:33:22 Evgeniy Polyakov wrote:
> On Sun, Apr 20, 2008 at 02:05:31AM +1000, Rusty Russell 
(rusty@...tcorp.com.au) wrote:
> > 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?

I don't think so, it just externalizes the locking.  The mutex protects the 
attaching and detaching of the ops structure, some other lock or code 
protects simultenous kernel ring accesses.

Cheers,
Rusty.
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