Date:   Mon, 17 Jun 2019 11:01:55 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Song Liu <liu.song.a23@...il.com>
Cc:     Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>
Subject: Re: [RFC PATCH bpf-next 3/8] libbpf: refactor map initialization

On Sat, Jun 15, 2019 at 2:03 PM Song Liu <liu.song.a23@...il.com> wrote:
>
> On Mon, Jun 10, 2019 at 9:35 PM Andrii Nakryiko <andriin@...com> wrote:
> >
> > User and global data maps initialization has gotten pretty complicated
> > and unnecessarily convoluted. This patch splits out the logic for global
> > data map and user-defined map initialization. It also removes the
> > restriction of pre-calculating how many maps will be initialized,
> > instead allowing to keep adding new maps as they are discovered, which
> > will be used later for BTF-defined map definitions.
> >
> > Signed-off-by: Andrii Nakryiko <andriin@...com>
> > ---
> >  tools/lib/bpf/libbpf.c | 244 ++++++++++++++++++++++-------------------
> >  1 file changed, 134 insertions(+), 110 deletions(-)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 9e39a0a33aeb..c931ee7e1fd2 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -234,6 +234,7 @@ struct bpf_object {
> >         size_t nr_programs;
> >         struct bpf_map *maps;
> >         size_t nr_maps;
> > +       size_t maps_cap;
> >         struct bpf_secdata sections;
> >
> >         bool loaded;
> > @@ -763,12 +764,38 @@ int bpf_object__variable_offset(const struct bpf_object *obj, const char *name,
> >         return -ENOENT;
> >  }
> >
> > -static bool bpf_object__has_maps(const struct bpf_object *obj)
> > +static struct bpf_map *bpf_object__add_map(struct bpf_object *obj)
> >  {
> > -       return obj->efile.maps_shndx >= 0 ||
> > -              obj->efile.data_shndx >= 0 ||
> > -              obj->efile.rodata_shndx >= 0 ||
> > -              obj->efile.bss_shndx >= 0;
> > +       struct bpf_map *new_maps;
> > +       size_t new_cap;
> > +       int i;
> > +
> > +       if (obj->nr_maps + 1 <= obj->maps_cap)
> nit:   how about     if (obj->nr_maps < obj->maps_cap)

yep, will do

>
> > +               return &obj->maps[obj->nr_maps++];
> > +
> > +       new_cap = max(4ul, obj->maps_cap * 3 / 2);
> > +       new_maps = realloc(obj->maps, new_cap * sizeof(*obj->maps));
> > +       if (!new_maps) {
> > +               pr_warning("alloc maps for object failed\n");
> > +               return ERR_PTR(-ENOMEM);
> > +       }
> > +
> > +       obj->maps_cap = new_cap;
> > +       obj->maps = new_maps;
> > +
> > +       /* zero out new maps */
> > +       memset(obj->maps + obj->nr_maps, 0,
> > +              (obj->maps_cap - obj->nr_maps) * sizeof(*obj->maps));
> > +       /*
> > +        * fill all fd with -1 so won't close incorrect fd (fd=0 is stdin)
> > +        * when failure (zclose won't close negative fd)).
> > +        */
> > +       for (i = obj->nr_maps; i < obj->maps_cap; i++) {
> > +               obj->maps[i].fd = -1;
> > +               obj->maps[i].inner_map_fd = -1;
> > +       }
> > +
> > +       return &obj->maps[obj->nr_maps++];
> >  }
> >
> >  static int
> > @@ -808,29 +835,68 @@ bpf_object__init_internal_map(struct bpf_object *obj, struct bpf_map *map,
> >         return 0;
> >  }
> >
> > -static int bpf_object__init_maps(struct bpf_object *obj, int flags)
> > +static int bpf_object__init_global_data_maps(struct bpf_object *obj)
> > +{
> > +       struct bpf_map *map;
> > +       int err;
> > +
> > +       if (!obj->caps.global_data)
> > +               return 0;
> > +       /*
> > +        * Populate obj->maps with libbpf internal maps.
> > +        */
> > +       if (obj->efile.data_shndx >= 0) {
> > +               map = bpf_object__add_map(obj);
> > +               if (IS_ERR(map))
> > +                       return PTR_ERR(map);
> > +               err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_DATA,
> > +                                                   obj->efile.data,
> > +                                                   &obj->sections.data);
> > +               if (err)
> > +                       return err;
> > +       }
> > +       if (obj->efile.rodata_shndx >= 0) {
> > +               map = bpf_object__add_map(obj);
> > +               if (IS_ERR(map))
> > +                       return PTR_ERR(map);
> > +               err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_RODATA,
> > +                                                   obj->efile.rodata,
> > +                                                   &obj->sections.rodata);
> > +               if (err)
> > +                       return err;
> > +       }
> > +       if (obj->efile.bss_shndx >= 0) {
> > +               map = bpf_object__add_map(obj);
> > +               if (IS_ERR(map))
> > +                       return PTR_ERR(map);
> > +               err = bpf_object__init_internal_map(obj, map, LIBBPF_MAP_BSS,
> > +                                                   obj->efile.bss, NULL);
> > +               if (err)
> > +                       return err;
> > +       }
>
> These 3 if clause are a little too complicated. How about we call
> bpf_obj_add_map(obj) within bpf_object__init_internal_map()?

Yeah, totally, not sure why I did it this way :)

>
> > +       return 0;
> > +}
> > +
> > +static int bpf_object__init_user_maps(struct bpf_object *obj, bool strict)
> >  {

<snip>

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