netdev - Re: [PATCH v3 bpf-next 00/11] bpf: revolutionize bpf tracing

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Message-ID: <20191017151445.GB26267@pc-63.home>
Date:   Thu, 17 Oct 2019 17:14:45 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <ast@...nel.org>
Cc:     davem@...emloft.net, x86@...nel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v3 bpf-next 00/11] bpf: revolutionize bpf tracing

On Tue, Oct 15, 2019 at 08:24:54PM -0700, Alexei Starovoitov wrote:
> v2->v3:
> - while trying to adopt btf-based tracing in production service realized
>   that disabling bpf_probe_read() was premature. The real tracing program
>   needs to see much more than this type safe tracking can provide.
>   With these patches the verifier will be able to see that skb->data
>   is a pointer to 'u8 *', but it cannot possibly know how many bytes
>   of it is readable. Hence bpf_probe_read() is necessary to do basic
>   packet reading from tracing program. Some helper can be introduced to
>   solve this particular problem, but there are other similar structures.
>   Another issue is bitfield reading. The support for bitfields
>   is coming to llvm. libbpf will be supporting it eventually as well,
>   but there will be corner cases where bpf_probe_read() is necessary.
>   The long term goal is still the same: get rid of probe_read eventually.
> - fixed build issue with clang reported by Nathan Chancellor.
> - addressed a ton of comments from Andrii.
>   bitfields and arrays are explicitly unsupported in btf-based tracking.
>   This will be improved in the future.
>   Right now the verifier is more strict than necessary.
>   In some cases it can fall back to 'scalar' instead of rejecting
>   the program, but rejection today allows to make better decisions
>   in the future.
> - adjusted testcase to demo bitfield and skb->data reading.

Applied, thanks!