[dpdk-dev] [PATCH 2/5] mbuf: use the reserved 16 bits for double vlan

[Stephen Hemminger]

On Tue, 26 May 2015 15:02:51 +0000
"Ananyev, Konstantin" <konstantin.ananyev at intel.com> wrote:

> Hi Stephen,
> 
> > -----Original Message-----
> > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Stephen Hemminger
> > Sent: Tuesday, May 26, 2015 3:55 PM
> > To: Zhang, Helin
> > Cc: dev at 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 at 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 at 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.
Yes, it would be dumb of application to do that but from absolute ABI point
of view it is a change.