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Date:   Wed, 25 Sep 2019 06:33:43 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Matt Cover <werekraken@gmail.com>
Cc:     davem@davemloft.net, ast@kernel.org, daniel@iogearbox.net,
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        linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Subject: Re: [PATCH net-next] tuntap: Fallback to automq on
 TUNSETSTEERINGEBPF prog negative return
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On Sun, Sep 22, 2019 at 03:46:19PM -0700, Matt Cover wrote:
> Unless of course we can simply state via
> documentation that any negative return
> for which a define doesn't exist is
> undefined behavior. In which case,
> there is no old vs new behavior and
> no need for an ioctl. Simply the
> understanding provided by the
> documentation.

Unfortunately this isn't sufficient: software can easily return a wrong
value by mistake, and become dependent on an undefined behaviour.

-- 
MST