netdev - Re: [PATCH bpf-next 1/2] net: xdp: refactor XDP_QUERY_PROG{,

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Date:   Wed, 22 May 2019 14:04:47 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/2] net: xdp: refactor XDP_QUERY_PROG{,_HW} to
 netdev

On Wed, 22 May 2019 22:54:44 +0200, Björn Töpel wrote:
> > > Now, the same commands give:
> > >
> > >   # ip link set dev eth0 xdp obj foo.o sec main
> > >   # ip link set dev eth0 xdpgeneric off
> > >   Error: native and generic XDP can't be active at the same time.  
> >
> > I'm not clear why this change is necessary? It is a change in
> > behaviour, and if anything returning ENOENT would seem cleaner
> > in this case.
> 
> To me, the existing behavior was non-intuitive. If most people *don't*
> agree, I'll remove this change. So, what do people think about this?
> :-)

Having things start to fail after they were successful/ignored
is one of those ABI breakage types Linux and netdev usually takes
pretty seriously, unfortunately.  Especially when motivation is 
"it's more intuitive" :)

If nobody chimes in please break out this behaviour change into 
a commit of its own.

> ENOENT does make more sense.