linux-kernel - Re: [PATCH bpf-next] libbpf: Add bpf_object_

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Date:   Wed, 23 Aug 2023 10:19:10 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Daniel Xu <dxu@...uu.xyz>
Cc:     ast@...nel.org, andrii@...nel.org, daniel@...earbox.net,
        martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next] libbpf: Add bpf_object__unpin()

On Tue, Aug 22, 2023 at 10:44 PM Daniel Xu <dxu@...uu.xyz> wrote:
>
> For bpf_object__pin_programs() there is bpf_object__unpin_programs().
> Likewise bpf_object__unpin_maps() for bpf_object__pin_maps().
>
> But no bpf_object__unpin() for bpf_object__pin(). Adding the former adds
> symmetry to the API.
>
> It's also convenient for cleanup in application code. It's an API I
> would've used if it was available for a repro I was writing earlier.
>
> Signed-off-by: Daniel Xu <dxu@...uu.xyz>
> ---
>  tools/lib/bpf/libbpf.c   | 15 +++++++++++++++
>  tools/lib/bpf/libbpf.h   |  1 +
>  tools/lib/bpf/libbpf.map |  1 +
>  3 files changed, 17 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 4c3967d94b6d..96ff1aa4bf6a 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -8376,6 +8376,21 @@ int bpf_object__pin(struct bpf_object *obj, const char *path)
>         return 0;
>  }
>
> +int bpf_object__unpin(struct bpf_object *obj, const char *path)
> +{
> +       int err;
> +
> +       err = bpf_object__unpin_programs(obj, path);
> +       if (err)
> +               return libbpf_err(err);
> +
> +       err = bpf_object__unpin_maps(obj, path);
> +       if (err)
> +               return libbpf_err(err);
> +
> +       return 0;
> +}
> +

pin APIs predate me, and I barely ever use them, but I wonder if
people feel fine with the fact that if any single unpin fails, all the
other programs/maps will not be unpinned? I also wonder if the best
effort unpinning of everything (while propagating first/last error) is
more practical? Looking at bpf_object__pin_programs, we try unpin
everything, even if some unpins fail.

Any thoughts or preferences?

>  static void bpf_map__destroy(struct bpf_map *map)
>  {
>         if (map->inner_map) {
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 2e3eb3614c40..0e52621cba43 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -266,6 +266,7 @@ LIBBPF_API int bpf_object__pin_programs(struct bpf_object *obj,
>  LIBBPF_API int bpf_object__unpin_programs(struct bpf_object *obj,
>                                           const char *path);
>  LIBBPF_API int bpf_object__pin(struct bpf_object *object, const char *path);
> +LIBBPF_API int bpf_object__unpin(struct bpf_object *object, const char *path);
>
>  LIBBPF_API const char *bpf_object__name(const struct bpf_object *obj);
>  LIBBPF_API unsigned int bpf_object__kversion(const struct bpf_object *obj);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 841a2f9c6fef..abf8fea3988e 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -399,4 +399,5 @@ LIBBPF_1.3.0 {
>                 bpf_program__attach_netfilter;
>                 bpf_program__attach_tcx;
>                 bpf_program__attach_uprobe_multi;
> +               bpf_object__unpin;
>  } LIBBPF_1.2.0;
> --
> 2.41.0
>