netdev - Re: [PATCH v2 bpf-next 1/2] bpf: replace prog_raw_tp+btf_id with prog

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Message-ID: <5ef95166-dace-28be-8274-a9343900025e@iogearbox.net>
Date:   Fri, 1 Nov 2019 00:20:13 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v2 bpf-next 1/2] bpf: replace prog_raw_tp+btf_id with
 prog_tracing

On 10/30/19 11:32 PM, Alexei Starovoitov wrote:
> The bpf program type raw_tp together with 'expected_attach_type'
> was the most appropriate api to indicate BTF-enabled raw_tp programs.
> But during development it became apparent that 'expected_attach_type'
> cannot be used and new 'attach_btf_id' field had to be introduced.
> Which means that the information is duplicated in two fields where
> one of them is ignored.
> Clean it up by introducing new program type where both
> 'expected_attach_type' and 'attach_btf_id' fields have
> specific meaning.

Hm, just for my understanding, the expected_attach_type is unused for
tracing so far. Are you aware of anyone (bcc / bpftrace / etc) leaving
uninitialized garbage in there? Just seems confusing that we have all
the different tracing prog types and now adding yet another one as
BPF_RPOG_TYPE_TRACING which will act as umbrella one and again have
different attach types some of which probably resemble existing tracing
prog types again (kprobes / kretprobes for example). Sounds like this
new type would implicitly deprecate all the existing types (sort of as
we're replacing them with new sub-types)?

True that k[ret]probe expects pt_regs whereas BTF enabled program context
will be the same as raw_tp as well, but couldn't this logic be hidden in
the kernel e.g. via attach_btf_id as well since this is an opt-in? Could
the fentry/fexit be described through attach_btf_id as well?

> In the future 'expected_attach_type' will be extended
> with other attach points that have similar semantics to raw_tp.
> This patch is replacing BTF-enabled BPF_PROG_TYPE_RAW_TRACEPOINT with
> prog_type = BPF_RPOG_TYPE_TRACING
> expected_attach_type = BPF_TRACE_RAW_TP
> attach_btf_id = btf_id of raw tracepoint inside the kernel
> Future patches will add
> expected_attach_type = BPF_TRACE_FENTRY or BPF_TRACE_FEXIT
> where programs have the same input context and the same helpers,
> but different attach points.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> Acked-by: Andrii Nakryiko <andriin@...com>

Thanks,
Daniel