WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [PATCH] shared_info size and padding fixes

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] shared_info size and padding fixes
From: John Levon <levon@xxxxxxxxxxxxxxxxx>
Date: Thu, 10 Aug 2006 14:34:01 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Jan Beulich <jbeulich@xxxxxxxxxx>
Delivery-date: Thu, 10 Aug 2006 06:34:25 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <C100F345.BBF%Keir.Fraser@xxxxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
References: <20060810121348.GA24928@xxxxxxxxxxxxxxxxxxxx> <C100F345.BBF%Keir.Fraser@xxxxxxxxxxxx>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
User-agent: Mutt/1.5.9i
On Thu, Aug 10, 2006 at 02:29:25PM +0100, Keir Fraser wrote:

> > No, see the previous discussion with Keir - changing the size of the
> > shared info structure is apparently not part of the ABI (hence the
> > reason for the patch and the explanation above!)
> > 
> > Personally this seems unusual at best to me, but that's the way it is,
> > and furthermore has already happened with "nmi_reason".
> 
> Your patch looked fine, by the way, except that adding padding to every
> arch-specific portion of shared info seems unnecessary.

Imagine we want to add a new field to shared_info. It has to go after
the "arch" member, or offsets break. Once this happens, none of the
arch_shared_info's can be modified at all, as this will break the offset
of the new member.

It seems vastly better to provide some headroom *now* than to make a
mistake later.

regards
john

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel