Re: [PATCH 0/8] bpf: Add fprobe link

Masami Hiramatsu
2022-02-18T04:07:40Z

On Thu, 17 Feb 2022 14:01:30 -0800
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:

> > > Is there any chance to support this fast multi-attach for uprobe? If
> > > yes, we might want to reuse the same link for both (so should we name
> > > it more generically?
> >
> > There is no interface to do that but also there is no limitation to
> > expand uprobes. For the kprobes, there are some limitations for the
> > function entry because it needs to share the space with ftrace. So
> > I introduced fprobe for easier to use.
> >
> > > on the other hand BPF program type for uprobe is
> > > BPF_PROG_TYPE_KPROBE anyway, so keeping it as "kprobe" also would be
> > > consistent with what we have today).
> >
> > Hmm, I'm not sure why BPF made such design choice... (Uprobe needs
> > the target program.)
> >
>
> We've been talking about sleepable uprobe programs, so we might need
> to add uprobe-specific program type, probably. But historically, from
> BPF point of view there was no difference between kprobe and uprobe
> programs (in terms of how they are run and what's available to them).
> From BPF point of view, it was just attaching BPF program to a
> perf_event.

Got it, so that will reuse the uprobe_events in ftrace. But I think
the uprobe requires a "path" to the attached binary, how is it
specified?

> > > But yeah, the main question is whether there is something preventing
> > > us from supporting multi-attach uprobe as well? It would be really
> > > great for USDT use case.
> >
> > Ah, for the USDT, it will be useful. But since now we will have "user-event"
> > which is faster than uprobes, we may be better to consider to use it.
>
> Any pointers? I'm not sure what "user-event" refers to.

Here is the user-events series, which allows user program to define
raw dynamic events and it can write raw event data directly from
user space.

https://lore.kernel.org/all/20220118204326.2169-1-beaub@linux.microsoft.com/

Thank you,

--
Masami Hiramatsu <mhiramat@kernel.org>