netdev - Re: [PATCH bpf-next 2/7] bpf: introduce bpf subcommand BPF_PERF_EVENT

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Message-ID: <20180516112734.GE12217@hirez.programming.kicks-ass.net>
Date:   Wed, 16 May 2018 13:27:34 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH bpf-next 2/7] bpf: introduce bpf subcommand
 BPF_PERF_EVENT_QUERY

On Tue, May 15, 2018 at 04:45:16PM -0700, Yonghong Song wrote:
> Currently, suppose a userspace application has loaded a bpf program
> and attached it to a tracepoint/kprobe/uprobe, and a bpf
> introspection tool, e.g., bpftool, wants to show which bpf program
> is attached to which tracepoint/kprobe/uprobe. Such attachment
> information will be really useful to understand the overall bpf
> deployment in the system.
> 
> There is a name field (16 bytes) for each program, which could
> be used to encode the attachment point. There are some drawbacks
> for this approaches. First, bpftool user (e.g., an admin) may not
> really understand the association between the name and the
> attachment point. Second, if one program is attached to multiple
> places, encoding a proper name which can imply all these
> attachments becomes difficult.
> 
> This patch introduces a new bpf subcommand BPF_PERF_EVENT_QUERY.
> Given a pid and fd, if the <pid, fd> is associated with a
> tracepoint/kprobe/uprobea perf event, BPF_PERF_EVENT_QUERY will return
>    . prog_id
>    . tracepoint name, or
>    . k[ret]probe funcname + offset or kernel addr, or
>    . u[ret]probe filename + offset
> to the userspace.
> The user can use "bpftool prog" to find more information about
> bpf program itself with prog_id.
> 
> Signed-off-by: Yonghong Song <yhs@...com>
> ---
>  include/linux/trace_events.h |  15 ++++++
>  include/uapi/linux/bpf.h     |  25 ++++++++++
>  kernel/bpf/syscall.c         | 113 +++++++++++++++++++++++++++++++++++++++++++
>  kernel/trace/bpf_trace.c     |  53 ++++++++++++++++++++
>  kernel/trace/trace_kprobe.c  |  29 +++++++++++
>  kernel/trace/trace_uprobe.c  |  22 +++++++++
>  6 files changed, 257 insertions(+)

Why is the command called *_PERF_EVENT_* ? Are there not a lot of !perf
places to attach BPF proglets?