Re: [PATCH bpf-next] libbpf: export bpf_object__reuse_map() to libbpf api

[Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx>]

On Thu, Oct 1, 2020 at 4:34 AM Hangbin Liu <liuhangbin@xxxxxxxxx> wrote:
>
> On Thu, 1 Oct 2020 at 02:30, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index 32dc444224d8..5412aa7169db 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -4215,7 +4215,7 @@ bpf_object__create_maps(struct bpf_object *obj)
> > >                 if (map->fd >= 0) {
> > >                         pr_debug("map '%s': skipping creation (preset fd=%d)\n",
> > >                                  map->name, map->fd);
> > > -                       continue;
> > > +                       goto check_pin_path;
> > >                 }
> > >
> > >                 err = bpf_object__create_map(obj, map);
> > > @@ -4258,6 +4258,7 @@ bpf_object__create_maps(struct bpf_object *obj)
> > >                         map->init_slots_sz = 0;
> > >                 }
> > >
> > > +check_pin_path:
> > >                 if (map->pin_path && !map->pinned) {
> > >                         err = bpf_map__pin(map, NULL);
> > >                         if (err) {
> > >
> > >
> > > Do you think if this change be better?
> >
> > Yes, of course. Just don't do it through use of goto. Guard map
> > creation with that if instead.
>
> Hi Andrii,
>
> Looks I missed something, Would you like to explain why we should not use goto?

Because goto shouldn't be a default way of altering the control flow.

> And for "guard map creation with the if", do you mean duplicate the
> if (map->pin_path && !map->pinned) in if (map->fd >= 0)? like

I mean something like:


if (map->pin_path) { ... }

if (map fd < 0) {
  bpf_object__create_map(..);
  if (bpf_map__is_internal(..)) { ... }
  if (map->init_slot_sz) { ...}
}

if (map->pin_path && !map->pinned) { ...  }


>
> diff --git a/src/libbpf.c b/src/libbpf.c
> index 3df1f4d..705abcb 100644
> --- a/src/libbpf.c
> +++ b/src/libbpf.c
> @@ -4215,6 +4215,15 @@ bpf_object__create_maps(struct bpf_object *obj)
>                 if (map->fd >= 0) {
>                         pr_debug("map '%s': skipping creation (preset fd=%d)\n",
>                                  map->name, map->fd);
> +                       if (map->pin_path && !map->pinned) {
> +                               err = bpf_map__pin(map, NULL);
> +                               if (err) {
> +                                       pr_warn("map '%s': failed to
> auto-pin at '%s': %d\n",
> +                                               map->name, map->pin_path, err);
> +                                       zclose(map->fd);
> +                                       goto err_out;
> +                               }
> +                       }
>                         continue;
>                 }
>
> (Sorry if the code format got corrupted as I replied in web gmail....)
>
> Thanks
> Hangbin