netdev - Re: [RFC PATCH bpf-next] xdp: Add tracepoint on XDP program return

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Date:   Mon, 16 Dec 2019 19:17:59 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Ido Schimmel <idosch@...sch.org>
Subject: Re: [RFC PATCH bpf-next] xdp: Add tracepoint on XDP program return

On Mon, 16 Dec 2019 at 16:28, Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> This adds a new tracepoint, xdp_prog_return, which is triggered at every
> XDP program return. This was first discussed back in August[0] as a way to
> hook XDP into the kernel drop_monitor framework, to have a one-stop place
> to find all packet drops in the system.
>
> Because trace/events/xdp.h includes filter.h, some ifdef guarding is needed
> to be able to use the tracepoint from bpf_prog_run_xdp(). If anyone has any
> ideas for how to improve on this, please to speak up. Sending this RFC
> because of this issue, and to get some feedback from Ido on whether this
> tracepoint has enough data for drop_monitor usage.
>

I get that it would be useful, but can it be solved with BPF tracing
(i.e. tracing BPF with BPF)? It would be neat not adding another
tracepoint in the fast-path...