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Date: Thu, 18 Sep 2014 19:28:04 +0200
From: Daniel Borkmann <dborkman@redhat.com>
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To: Alexei Starovoitov <ast@plumgrid.com>
CC: "David S. Miller" <davem@davemloft.net>, Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Peter Zijlstra <a.p.zijlstra@chello.nl>,
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        "H. Peter Anvin" <hpa@zytor.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Linux API <linux-api@vger.kernel.org>,
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Subject: Re: [PATCH v13 net-next 07/11] bpf: verifier (add ability to receive
 verification log)
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On 09/18/2014 05:24 PM, Alexei Starovoitov wrote:
...
> solve or not. If we decide to solve it, we need to have
> a plan to solve it all the way. Partial fix for size of bpf_attr
> is not a plan. It's something that is not addressing the problem
> completely. Little bit of help is not useful for userspace. It
> would need to deal with new types, verifier differences and
> other things that I mentioned earlier.

Hm, I don't think it would be a strict requirement to solve it
all the way, and I think that perf_event_open() with perf_copy_attr()
is not trying to do so either. It, however, is trying on a ``best
effort basis'' to still load something if new features are unused
by the binary (I guess you saw the comment in perf_copy_attr()).

Iff, e.g. due to new types we fail at the verifier stage, sure,
that's life since we only have backwards-compatible guarantee,
but in case we tried to use features we support, we're still able
to load the eBPF program while right now, we're rejecting it right
up-front. That's just my $0.02 ...