linux-kernel - Re: [PATCH net-next] tuntap: Fallback to automq on TUNSETSTEERINGEBPF prog negative return

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Message-ID: <20190925063142-mutt-send-email-mst@kernel.org>
Date:   Wed, 25 Sep 2019 06:33:43 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Matt Cover <werekraken@...il.com>
Cc:     davem@...emloft.net, ast@...nel.org, daniel@...earbox.net,
        kafai@...com, songliubraving@...com, yhs@...com,
        Jason Wang <jasowang@...hat.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Matthew Cover <matthew.cover@...ckpath.com>,
        mail@...urcelik.de, pabeni@...hat.com,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        wangli39@...du.com, lifei.shirley@...edance.com,
        tglx@...utronix.de, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next] tuntap: Fallback to automq on
 TUNSETSTEERINGEBPF prog negative return

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