Re: [PATCH bpf-next 6/8] libbpf: Add support for bpf_link-based netns attachment

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, May 27, 2020 at 12:16 PM Jakub Sitnicki <jakub@cloudflare.com> wrote:
>
> Add bpf_program__attach_nets(), which uses LINK_CREATE subcommand to create
> an FD-based kernel bpf_link, for attach types tied to network namespace,
> that is BPF_FLOW_DISSECTOR for the moment.
>
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
>  tools/lib/bpf/libbpf.c   | 20 ++++++++++++++++----
>  tools/lib/bpf/libbpf.h   |  2 ++
>  tools/lib/bpf/libbpf.map |  1 +
>  3 files changed, 19 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 5d60de6fd818..a49c1eb5db64 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -7894,8 +7894,8 @@ static struct bpf_link *attach_iter(const struct bpf_sec_def *sec,
>         return bpf_program__attach_iter(prog, NULL);
>  }
>
> -struct bpf_link *
> -bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
> +static struct bpf_link *
> +bpf_program__attach_fd(struct bpf_program *prog, int target_fd)
>  {
>         enum bpf_attach_type attach_type;
>         char errmsg[STRERR_BUFSIZE];
> @@ -7915,11 +7915,11 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>         link->detach = &bpf_link__detach_fd;
>
>         attach_type = bpf_program__get_expected_attach_type(prog);
> -       link_fd = bpf_link_create(prog_fd, cgroup_fd, attach_type, NULL);
> +       link_fd = bpf_link_create(prog_fd, target_fd, attach_type, NULL);
>         if (link_fd < 0) {
>                 link_fd = -errno;
>                 free(link);
> -               pr_warn("program '%s': failed to attach to cgroup: %s\n",
> +               pr_warn("program '%s': failed to attach to cgroup/netns: %s\n",

I understand the desire to save few lines of code, but it hurts error
reporting. Now it's cgroup/netns, tomorrow cgroup/netns/lirc/whatever.
If you want to generalize, let's preserve clarity of error message,
please.

>                         bpf_program__title(prog, false),
>                         libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
>                 return ERR_PTR(link_fd);
> @@ -7928,6 +7928,18 @@ bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
>         return link;
>  }
>
> +struct bpf_link *
> +bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd)
> +{
> +       return bpf_program__attach_fd(prog, cgroup_fd);
> +}
> +
> +struct bpf_link *
> +bpf_program__attach_netns(struct bpf_program *prog, int netns_fd)
> +{
> +       return bpf_program__attach_fd(prog, netns_fd);
> +}
> +
>  struct bpf_link *
>  bpf_program__attach_iter(struct bpf_program *prog,
>                          const struct bpf_iter_attach_opts *opts)
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 1e2e399a5f2c..adf6fd9b6fe8 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -253,6 +253,8 @@ LIBBPF_API struct bpf_link *
>  bpf_program__attach_lsm(struct bpf_program *prog);
>  LIBBPF_API struct bpf_link *
>  bpf_program__attach_cgroup(struct bpf_program *prog, int cgroup_fd);
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_netns(struct bpf_program *prog, int netns_fd);
>
>  struct bpf_map;
>
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 381a7342ecfc..7ad21ba1feb6 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -263,4 +263,5 @@ LIBBPF_0.0.9 {
>                 bpf_link_get_next_id;
>                 bpf_program__attach_iter;
>                 perf_buffer__consume;
> +               bpf_program__attach_netns;

Please keep it alphabetical.

>  } LIBBPF_0.0.8;
> --
> 2.25.4
>