Re: [PATCH bpf-next v4 4/5] libbpf: Add auto-pinning of maps when loading BPF objects

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Andrii Nakryiko <andrii.nakryiko@gmail.com> writes:

> On Thu, Oct 31, 2019 at 10:37 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
>>
>> On Tue, Oct 29, 2019 at 12:39 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>> >
>> > From: Toke Høiland-Jørgensen <toke@redhat.com>
>> >
>> > This adds support to libbpf for setting map pinning information as part of
>> > the BTF map declaration, to get automatic map pinning (and reuse) on load.
>> > The pinning type currently only supports a single PIN_BY_NAME mode, where
>> > each map will be pinned by its name in a path that can be overridden, but
>> > defaults to /sys/fs/bpf.
>> >
>> > Since auto-pinning only does something if any maps actually have a
>> > 'pinning' BTF attribute set, we default the new option to enabled, on the
>> > assumption that seamless pinning is what most callers want.
>> >
>> > When a map has a pin_path set at load time, libbpf will compare the map
>> > pinned at that location (if any), and if the attributes match, will re-use
>> > that map instead of creating a new one. If no existing map is found, the
>> > newly created map will instead be pinned at the location.
>> >
>> > Programs wanting to customise the pinning can override the pinning paths
>> > using bpf_map__set_pin_path() before calling bpf_object__load() (including
>> > setting it to NULL to disable pinning of a particular map).
>> >
>> > Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> > ---
>>
>> Please fix unconditional pin_path setting, with that:
>>
>> Acked-by: Andrii Nakryiko <andriin@fb.com>
>>
>> >  tools/lib/bpf/bpf_helpers.h |    6 ++
>> >  tools/lib/bpf/libbpf.c      |  144 +++++++++++++++++++++++++++++++++++++++++--
>> >  tools/lib/bpf/libbpf.h      |   13 ++++
>> >  3 files changed, 154 insertions(+), 9 deletions(-)
>> >
>> > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
>> > index 2203595f38c3..0c7d28292898 100644
>> > --- a/tools/lib/bpf/bpf_helpers.h
>> > +++ b/tools/lib/bpf/bpf_helpers.h
>> > @@ -38,4 +38,10 @@ struct bpf_map_def {
>> >         unsigned int map_flags;
>> >  };
>> >
>>
>> [...]
>>
>> > @@ -1270,6 +1292,28 @@ static int bpf_object__init_user_btf_map(struct bpf_object *obj,
>> >                         }
>> >                         map->def.value_size = sz;
>> >                         map->btf_value_type_id = t->type;
>> > +               } else if (strcmp(name, "pinning") == 0) {
>> > +                       __u32 val;
>> > +                       int err;
>> > +
>> > +                       if (!get_map_field_int(map_name, obj->btf, def, m,
>> > +                                              &val))
>> > +                               return -EINVAL;
>> > +                       pr_debug("map '%s': found pinning = %u.\n",
>> > +                                map_name, val);
>> > +
>> > +                       if (val != LIBBPF_PIN_NONE &&
>> > +                           val != LIBBPF_PIN_BY_NAME) {
>> > +                               pr_warn("map '%s': invalid pinning value %u.\n",
>> > +                                       map_name, val);
>> > +                               return -EINVAL;
>> > +                       }
>> > +                       err = build_map_pin_path(map, pin_root_path);
>>
>> uhm... only if (val == LIBBPF_PIN_BY_NAME)?.. maybe extend tests with
>> a mix if auto-pinned and never pinned map to catch issue like this?
>
> I was wondering why your selftest didn't catch this, got puzzled for a
> bit. It's because this code path will be executed only when map
> defintion has __uint(pinning, LIBBPF_PIN_NONE), can you please add
> that to selftest as well?

Can do :)

-Toke