From mboxrd@z Thu Jan  1 00:00:00 1970
From: Stephen Hemminger <stephen@networkplumber.org>
Subject: Re: [PATCH v4 1/2] mbuf: support attaching external
 buffer to mbuf
Date: Wed, 25 Apr 2018 08:06:29 -0700
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Cc: Olivier Matz <olivier.matz@6wind.com>, Andrew Rybchenko
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To: Thomas Monjalon <thomas@monjalon.net>
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On Tue, 24 Apr 2018 22:22:45 +0200
Thomas Monjalon <thomas@monjalon.net> wrote:

> > > 
> > > I guess the problem that it changes INDIRECT semantics since EXTBUF
> > > is added as well. I think strictly speaking it is an API change.
> > > Is it OK to make it without announcement?  
> > 
> > In any case, there will be an ABI change, because an application
> > compiled for 18.02 will not be able to handle these new kind of
> > mbuf.
> > 
> > So unfortunatly yes, I think this kind of changes should first be
> > announced.
> > 
> > Thomas, what do you think?  
> 
> What is the impact for the application developer?
> Is there something to change in the application after this patch?

Maybe the use of external buffers should be negotiated as a receiver
flag (per queue) in the device driver.  If device wants external buffers
it sets that in capability flag, and only uses it application requests
it. This allows old applications to work with no semantic surprises.