From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [Patch net-next] net: clean up skb headers code
Date: Thu, 30 May 2013 03:40:21 -0700 (PDT)
Message-ID: <20130530.034021.851099674189749250.davem@davemloft.net>
References: <1369807740-12324-1-git-send-email-amwang@redhat.com>
	<20130528.233647.1209227470109213894.davem@davemloft.net>
	<1369856073.1971.2.camel@bwh-desktop.uk.level5networks.com>
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: amwang@redhat.com, netdev@vger.kernel.org, horms@verge.net.au
To: bhutchings@solarflare.com
Return-path: <netdev-owner@vger.kernel.org>
Received: from shards.monkeyblade.net ([149.20.54.216]:46041 "EHLO
	shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1030549Ab3E3KkY (ORCPT
	<rfc822;netdev@vger.kernel.org>); Thu, 30 May 2013 06:40:24 -0400
In-Reply-To: <1369856073.1971.2.camel@bwh-desktop.uk.level5networks.com>
Sender: netdev-owner@vger.kernel.org
List-ID: <netdev.vger.kernel.org>

From: Ben Hutchings <bhutchings@solarflare.com>
Date: Wed, 29 May 2013 20:34:33 +0100

> On Tue, 2013-05-28 at 23:36 -0700, David Miller wrote:
>> From: Cong Wang <amwang@redhat.com>
>> Date: Wed, 29 May 2013 14:09:00 +0800
>> 
>> > commit 1a37e412a0225fcba5587 (net: Use 16bits for *_headers
>> > fields of struct skbuff) converts skb->*_header to u16,
>> > therefore 1) we could just use 0xFFFFF instead of (__u16) ~0U
>> > 2) some #if NET_SKBUFF_DATA_USES_OFFSET is useless now.
>> > 
>> > 
>> > Cc: David S. Miller <davem@davemloft.net>
>> > Cc: Simon Horman <horms@verge.net.au>
>> > Signed-off-by: Cong Wang <amwang@redhat.com>
>> 
>> I want to use something that will either break the build or
>> automatically work if the type changes again.
>> 
>> So something like "X = (typeof(X)) ~0U;".
> 
> I think you mean ~(typeof(X))0.

Take a look at what that does for ~(u8)0.

We had a bug fix in this are recently in ieee802154 if I remember
correctly.