From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Zhang, Helin" <helin.zhang@intel.com>
Subject: Re: [PATCH 2/5] mbuf: use the reserved 16 bits for
 double vlan
Date: Wed, 27 May 2015 01:07:41 +0000
Message-ID: <F35DEAC7BCE34641BA9FAC6BCA4A12E70A86C244@SHSMSX104.ccr.corp.intel.com>
References: <1430793143-3610-1-git-send-email-helin.zhang@intel.com>
 <1432629400-25303-1-git-send-email-helin.zhang@intel.com>
 <1432629400-25303-3-git-send-email-helin.zhang@intel.com>
 <20150526075515.1bc42ae1@urahara>
 <2601191342CEEE43887BDE71AB97725821431C8F@irsmsx105.ger.corp.intel.com>
 <20150526083505.247e5431@urahara>
 <2601191342CEEE43887BDE71AB97725821431D05@irsmsx105.ger.corp.intel.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
Cc: "dev@dpdk.org" <dev@dpdk.org>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>, Stephen Hemminger
 <stephen@networkplumber.org>
Return-path: <dev-bounces@dpdk.org>
Received: from mga09.intel.com (mga09.intel.com [134.134.136.24])
 by dpdk.org (Postfix) with ESMTP id E8F4A5A9A
 for <dev@dpdk.org>; Wed, 27 May 2015 03:07:57 +0200 (CEST)
In-Reply-To: <2601191342CEEE43887BDE71AB97725821431D05@irsmsx105.ger.corp.intel.com>
Content-Language: en-US
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
Errors-To: dev-bounces@dpdk.org
Sender: "dev" <dev-bounces@dpdk.org>



> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Tuesday, May 26, 2015 11:46 PM
> To: Stephen Hemminger
> Cc: Zhang, Helin; dev@dpdk.org
> Subject: RE: [dpdk-dev] [PATCH 2/5] mbuf: use the reserved 16 bits for
> double vlan
>=20
>=20
>=20
> > -----Original Message-----
> > From: Stephen Hemminger [mailto:stephen@networkplumber.org]
> > Sent: Tuesday, May 26, 2015 4:35 PM
> > To: Ananyev, Konstantin
> > Cc: Zhang, Helin; dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 2/5] mbuf: use the reserved 16 bits for
> > double vlan
> >
> > On Tue, 26 May 2015 15:02:51 +0000
> > "Ananyev, Konstantin" <konstantin.ananyev@intel.com> wrote:
> >
> > > Hi Stephen,
> > >
> > > > -----Original Message-----
> > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
> > > > Hemminger
> > > > Sent: Tuesday, May 26, 2015 3:55 PM
> > > > To: Zhang, Helin
> > > > Cc: dev@dpdk.org
> > > > Subject: Re: [dpdk-dev] [PATCH 2/5] mbuf: use the reserved 16 bits
> > > > for double vlan
> > > >
> > > > On Tue, 26 May 2015 16:36:37 +0800 Helin Zhang
> > > > <helin.zhang@intel.com> wrote:
> > > >
> > > > > Use the reserved 16 bits in rte_mbuf structure for the outer
> > > > > vlan, also add QinQ offloading flags for both RX and TX sides.
> > > > >
> > > > > Signed-off-by: Helin Zhang <helin.zhang@intel.com>
> > > >
> > > > Yet another change that is much needed, but breaks ABI
> compatibility.
> > >
> > > Why do you think it breaks ABI compatibility?
> > > As I can see, it uses field that was reserved.
> > > Konstantin
> >
> > Because an application maybe assuming something or reusing the
> reserved fields.
>=20
> But properly behaving application, shouldn't do that right?
> And for misbehaving ones, why should we care about them?
For any reserved bits, I think all application users should avoid touching =
it,
as it is reserved for future use, or some special reason. Otherwise,
un-predicted behavior can be expected.

Regards,
Helin

>=20
> > Yes, it would be dumb of application to do that but from absolute ABI
> > point of view it is a change.
>=20
> So, in theory,  even adding a new field to the end of rte_mbuf is an ABI
> breakage?
> Konstantin