Re: [PATCH bpf-next 4/5] bpf: Attach a cookie to a BPF program.

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Mon, Jan 31, 2022 at 10:47 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
> >  struct bpf_array_aux {
> > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> > index 16a7574292a5..3fa27346ab4b 100644
> > --- a/include/uapi/linux/bpf.h
> > +++ b/include/uapi/linux/bpf.h
> > @@ -1425,6 +1425,7 @@ union bpf_attr {
> >         struct { /* anonymous struct used by BPF_RAW_TRACEPOINT_OPEN command */
> >                 __u64 name;
> >                 __u32 prog_fd;
> > +               __u64 bpf_cookie;
> >         } raw_tracepoint;
> >
>
> As an aside, Alexei, should we bite a bullet and allow attaching
> raw_tp, fentry/fexit, and other tracing prog attachment through the
> LINK_CREATE command? BPF_RAW_TRACEPOINT_OPEN makes little sense for
> anything but raw_tp programs.

raw_tp_open is used for raw_tp, tp_btf, lsm, fentry.
iirc it's creating a normal bpf_link underneath.
link_create doesn't exist for raw_tp and friends,
so this is the best place to add a cookie.
We can add an alias cmd (instead of raw_tp_open)
to make it a bit cleaner from uapi naming pov.
We can allow link_create to do the attach in all those cases as well,
but it's a different discussion.
link_create.perf_event.bpf_cookie isn't the best name.
That name was a cause of confusion for me.
I thought it applies to perf_event only,
but it's for kuprobe too.
So plenty of bikeshedding to do if we decide to do
link_create for raw_tp. Hence, for now, I'd add a cookie to
raw_tp/tp_btf/lsm/fentry like this patch is doing.