From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ian Campbell <Ian.Campbell@citrix.com>
Subject: Re: Re: [PATCH 01/10] xen: Make all reserved pages for
	the balloon be INVALID_P2M_ENTRY.
Date: Wed, 22 Dec 2010 08:47:10 +0000
Message-ID: <1293007630.3998.36.camel@localhost.localdomain>
References: <1292967460-15709-1-git-send-email-konrad.wilk@oracle.com>
	<1292967460-15709-2-git-send-email-konrad.wilk@oracle.com>
	<4D1127FC.8060102@goop.org>
Mime-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <4D1127FC.8060102@goop.org>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: "xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Jan Beulich <JBeulich@novell.com>, Konrad Rzeszutek Wilk <konrad@kernel.org>, "hpa@zytor.com" <hpa@zytor.com>
List-Id: xen-devel@lists.xenproject.org

On Tue, 2010-12-21 at 22:19 +0000, Jeremy Fitzhardinge wrote: 
> On 12/21/2010 01:37 PM, Konrad Rzeszutek Wilk wrote:
> > +		BUG_ON(!set_phys_to_machine(pfn, INVALID_P2M_ENTRY));
[...] 
> I'm not a fan of hiding real side-effectful code in a BUG_ON
> predicate.
> 
> > +		BUG_ON(get_phys_to_machine(pfn) != INVALID_P2M_ENTRY);

I'm also not a fan of this "is the previous I called function buggy"
BUG_ON.

If we aren't confident that set_phys_to_machine() is doing the right
thing then adding a post-condition check to that function would be a
more preferable option.

Ian.