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

Peter Zijlstra
2018-05-16T11:27:46Z

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@fb.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?