Re: [RFC PATCH bpf-next 01/17] bpf: Link shimlink directly in trampoline

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Aug 08, 2022 at 10:58:36AM -0700, Stanislav Fomichev wrote:
> On Mon, Aug 8, 2022 at 10:40 AM Song Liu <song@kernel.org> wrote:
> >
> > On Mon, Aug 8, 2022 at 7:06 AM Jiri Olsa <jolsa@kernel.org> wrote:
> > >
> > > We are going to get rid of struct bpf_tramp_link in following
> > > changes and cgroup_shim_find logic does not fit to that.
> > >
> > > We can store the link directly in the trampoline and omit the
> > > cgroup_shim_find searching logic.
> > >
> > > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > > ---
> > >  include/linux/bpf.h     |  3 +++
> > >  kernel/bpf/trampoline.c | 23 +++--------------------
> > >  2 files changed, 6 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 20c26aed7896..ed2a921094bc 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -841,6 +841,8 @@ struct bpf_tramp_image {
> > >         };
> > >  };
> > >
> > > +struct bpf_shim_tramp_link;
> > > +
> > >  struct bpf_trampoline {
> > >         /* hlist for trampoline_table */
> > >         struct hlist_node hlist;
> > > @@ -868,6 +870,7 @@ struct bpf_trampoline {
> > >         struct bpf_tramp_image *cur_image;
> > >         u64 selector;
> > >         struct module *mod;
> > > +       struct bpf_shim_tramp_link *shim_link;
> > >  };
> >
> > Hi Stanislav,
> >
> > Is it possible to have multiple shim_link per bpf_trampoline? If so, I guess
> > this won't work.
> 
> There is only one shim_link per bpf_trampoline. But I'm not sure
> storing the pointer is enough. We have to do 'shim_link=NULL' when the
> (final) shim is removed. (multiple lsm_cgroup progs can share the same
> shim)

ok, will check on that

thanks,
jirka