From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Levon Subject: Re: [PATCH] shared_info size and padding fixes Date: Thu, 10 Aug 2006 14:34:01 +0100 Message-ID: <20060810133401.GA26023@totally.trollied.org> References: <20060810121348.GA24928@totally.trollied.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: xen-devel@lists.xensource.com, Jan Beulich List-Id: xen-devel@lists.xenproject.org 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