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

[Hangbin Liu <liuhangbin@gmail.com>]

On Thu, 1 Oct 2020 at 02:30, Andrii Nakryiko <andrii.nakryiko@gmail.com> 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?
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

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