netdev - Re: [PATCH bpf-next 1/3] libbpf: Store map pin path in struct bpf

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Message-ID: <CAEf4BzatAgkOiS2+EpauWsUWymmjM4YRBJcSqYj15Ywk8aP6Lw@mail.gmail.com>
Date:   Tue, 22 Oct 2019 10:37:17 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        David Miller <davem@...emloft.net>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 1/3] libbpf: Store map pin path in struct bpf_map

On Tue, Oct 22, 2019 at 9:08 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@...hat.com>
>
> When pinning a map, store the pin path in struct bpf_map so it can be
> re-used later for un-pinning. This simplifies the later addition of per-map
> pin paths.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  tools/lib/bpf/libbpf.c |   19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index cccfd9355134..b4fdd8ee3bbd 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -226,6 +226,7 @@ struct bpf_map {
>         void *priv;
>         bpf_map_clear_priv_t clear_priv;
>         enum libbpf_map_type libbpf_type;
> +       char *pin_path;
>  };
>
>  struct bpf_secdata {
> @@ -1929,6 +1930,7 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
>         if (err)
>                 goto err_close_new_fd;
>         free(map->name);
> +       zfree(&map->pin_path);
>

While you are touching this function, can you please also fix error
handling in it? We should store -errno locally on error, before we
call close() which might change errno.

>         map->fd = new_fd;
>         map->name = new_name;
> @@ -4022,6 +4024,7 @@ int bpf_map__pin(struct bpf_map *map, const char *path)
>                 return -errno;
>         }
>
> +       map->pin_path = strdup(path);

if (!map->pin_path) {
    err = -errno;
    goto err_close_new_fd;
}


>         pr_debug("pinned map '%s'\n", path);
>
>         return 0;
> @@ -4031,6 +4034,9 @@ int bpf_map__unpin(struct bpf_map *map, const char *path)
>  {
>         int err;
>
> +       if (!path)
> +               path = map->pin_path;

This semantics is kind of weird. Given we now remember pin_path,
should we instead check that user-provided path is actually correct
and matches what we stored? Alternatively, bpf_map__unpin() w/o path
argument looks like a cleaner API.

> +
>         err = check_path(path);
>         if (err)
>                 return err;
> @@ -4044,6 +4050,7 @@ int bpf_map__unpin(struct bpf_map *map, const char *path)
>         if (err != 0)
>                 return -errno;
>         pr_debug("unpinned map '%s'\n", path);
> +       zfree(&map->pin_path);
>
>         return 0;
>  }
> @@ -4088,17 +4095,10 @@ int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
>
>  err_unpin_maps:
>         while ((map = bpf_map__prev(map, obj))) {
> -               char buf[PATH_MAX];
> -               int len;
> -
> -               len = snprintf(buf, PATH_MAX, "%s/%s", path,
> -                              bpf_map__name(map));
> -               if (len < 0)
> -                       continue;
> -               else if (len >= PATH_MAX)
> +               if (!map->pin_path)
>                         continue;
>
> -               bpf_map__unpin(map, buf);
> +               bpf_map__unpin(map, NULL);
>         }
>
>         return err;
> @@ -4248,6 +4248,7 @@ void bpf_object__close(struct bpf_object *obj)
>
>         for (i = 0; i < obj->nr_maps; i++) {
>                 zfree(&obj->maps[i].name);
> +               zfree(&obj->maps[i].pin_path);
>                 if (obj->maps[i].clear_priv)
>                         obj->maps[i].clear_priv(&obj->maps[i],
>                                                 obj->maps[i].priv);
>