From owner-freebsd-xen@FreeBSD.ORG  Fri Jun 10 20:31:02 2011
Return-Path: <owner-freebsd-xen@FreeBSD.ORG>
Delivered-To: freebsd-xen@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 995BD106564A;
	Fri, 10 Jun 2011 20:31:02 +0000 (UTC)
	(envelope-from gibbs@FreeBSD.org)
Received: from aslan.scsiguy.com (aslan.scsiguy.com [70.89.174.89])
	by mx1.freebsd.org (Postfix) with ESMTP id 684548FC12;
	Fri, 10 Jun 2011 20:31:02 +0000 (UTC)
Received: from Justins-MacBook-Pro.local (207-225-98-3.dia.static.qwest.net
	[207.225.98.3]) (authenticated bits=0)
	by aslan.scsiguy.com (8.14.4/8.14.4) with ESMTP id p5AKV2gl062420
	(version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO);
	Fri, 10 Jun 2011 14:31:02 -0600 (MDT)
	(envelope-from gibbs@FreeBSD.org)
Message-ID: <4DF27EFF.5060005@FreeBSD.org>
Date: Fri, 10 Jun 2011 14:30:55 -0600
From: "Justin T. Gibbs" <gibbs@FreeBSD.org>
Organization: The FreeBSD Project
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US;
	rv:1.9.2.17) Gecko/20110414 Thunderbird/3.1.10
MIME-Version: 1.0
To: Colin Percival <cperciva@FreeBSD.org>
References: <4DF18EE5.5090704@freebsd.org>
In-Reply-To: <4DF18EE5.5090704@freebsd.org>
X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.6
	(aslan.scsiguy.com [70.89.174.89]);
	Fri, 10 Jun 2011 14:31:03 -0600 (MDT)
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
X-Content-Filtered-By: Mailman/MimeDel 2.1.5
Cc: "freebsd-xen@freebsd.org" <freebsd-xen@FreeBSD.org>
Subject: Re: breakage in blkfront with ring_pages > 1
X-BeenThere: freebsd-xen@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
Reply-To: gibbs@FreeBSD.org
List-Id: Discussion of the freebsd port to xen - implementation and usage
	<freebsd-xen.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-xen>,
	<mailto:freebsd-xen-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-xen>
List-Post: <mailto:freebsd-xen@freebsd.org>
List-Help: <mailto:freebsd-xen-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-xen>,
	<mailto:freebsd-xen-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Fri, 10 Jun 2011 20:31:02 -0000

On 6/9/11 9:26 PM, Colin Percival wrote:
>  Hi all,
>
>  I'm seeing breakage with ring_pages > 1 on a blkfront; more precisely, 
request
>  #32 has a garbage response (resulting in a panic) exactly as if the 
dom0 thinks
>  we're only using a single page for the ring. Forcing ring_pages to 1 
makes the
>  problem go away.
>
>  Has anyone seen anything like this? Is it possible that there's a bug 
in how
>  our blkfront negotiates the request ring? Does anyone have ring_pages 
 > 1 in
>  use?

The only backend driver I know of that can support more than one ring page
is FreeBSD.  So, the problem likely is that blkfront is getting the
negotiation wrong and only 1 page is in use.

--
Justin