netdev - Re: [PATCH bpf-next 2/5] bpftool: Do not expose and init hash maps for pinned path in main.c

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Date:   Fri, 22 Oct 2021 17:13:48 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 2/5] bpftool: Do not expose and init hash maps
 for pinned path in main.c

On Fri, Oct 22, 2021 at 10:16 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> BPF programs, maps, and links, can all be listed with their pinned paths
> by bpftool, when the "-f" option is provided. To do so, bpftool builds
> hash maps containing all pinned paths for each kind of objects.
>
> These three hash maps are always initialised in main.c, and exposed
> through main.h. There appear to be no particular reason to do so: we can
> just as well make them static to the files that need them (prog.c,
> map.c, and link.c respectively), and initialise them only when we want
> to show objects and the "-f" switch is provided.
>
> This may prevent unnecessary memory allocations if the implementation of
> the hash maps was to change in the future.
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  tools/bpf/bpftool/link.c |  9 ++++++++-
>  tools/bpf/bpftool/main.c | 12 ------------
>  tools/bpf/bpftool/main.h |  3 ---
>  tools/bpf/bpftool/map.c  |  9 ++++++++-
>  tools/bpf/bpftool/prog.c |  9 ++++++++-
>  5 files changed, 24 insertions(+), 18 deletions(-)
>
> diff --git a/tools/bpf/bpftool/link.c b/tools/bpf/bpftool/link.c
> index 8cc3e36f8cc6..ebf29be747b3 100644
> --- a/tools/bpf/bpftool/link.c
> +++ b/tools/bpf/bpftool/link.c
> @@ -20,6 +20,8 @@ static const char * const link_type_name[] = {
>         [BPF_LINK_TYPE_NETNS]                   = "netns",
>  };
>
> +static struct pinned_obj_table link_table;
> +
>  static int link_parse_fd(int *argc, char ***argv)
>  {
>         int fd;
> @@ -302,8 +304,10 @@ static int do_show(int argc, char **argv)
>         __u32 id = 0;
>         int err, fd;
>
> -       if (show_pinned)
> +       if (show_pinned) {
> +               hash_init(link_table.table);
>                 build_pinned_obj_table(&link_table, BPF_OBJ_LINK);
> +       }
>         build_obj_refs_table(&refs_table, BPF_OBJ_LINK);
>
>         if (argc == 2) {
> @@ -384,6 +388,9 @@ static int do_detach(int argc, char **argv)
>         if (json_output)
>                 jsonw_null(json_wtr);
>
> +       if (show_pinned)
> +               delete_pinned_obj_table(&link_table);

Shouldn't this be in do_show rather than do_detach?

> +
>         return 0;
>  }
>

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