Re: [PATCH bpf-next v2 4/7] libbpf: Add link-based API for tcx

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On Wed, Jun 7, 2023 at 12:26 PM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
>
> Implement tcx BPF link support for libbpf.
>
> The bpf_program__attach_fd_opts() API has been refactored slightly in order to
> pass bpf_link_create_opts pointer as input.
>
> A new bpf_program__attach_tcx_opts() has been added on top of this which allows
> for passing all relevant data via extensible struct bpf_tcx_opts.
>
> The program sections tcx/ingress and tcx/egress correspond to the hook locations
> for tc ingress and egress, respectively.
>
> For concrete usage examples, see the extensive selftests that have been
> developed as part of this series.
>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> ---
>  tools/lib/bpf/bpf.c      |  5 +++++
>  tools/lib/bpf/bpf.h      |  7 +++++++
>  tools/lib/bpf/libbpf.c   | 44 +++++++++++++++++++++++++++++++++++-----
>  tools/lib/bpf/libbpf.h   | 17 ++++++++++++++++
>  tools/lib/bpf/libbpf.map |  1 +
>  5 files changed, 69 insertions(+), 5 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index a3d1b7ebe224..c340d3cbc6bd 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -746,6 +746,11 @@ int bpf_link_create(int prog_fd, int target_fd,
>                 if (!OPTS_ZEROED(opts, tracing))
>                         return libbpf_err(-EINVAL);
>                 break;
> +       case BPF_TCX_INGRESS:
> +       case BPF_TCX_EGRESS:
> +               attr.link_create.tcx.relative_fd = OPTS_GET(opts, tcx.relative_fd, 0);
> +               attr.link_create.tcx.expected_revision = OPTS_GET(opts, tcx.expected_revision, 0);

can you also add an OPTS_ZEROED check like for other types of links?

> +               break;
>         default:
>                 if (!OPTS_ZEROED(opts, flags))
>                         return libbpf_err(-EINVAL);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index 480c584a6f7f..12591516dca0 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -370,6 +370,13 @@ struct bpf_link_create_opts {
>                 struct {
>                         __u64 cookie;
>                 } tracing;
> +               struct {
> +                       union {
> +                               __u32 relative_fd;
> +                               __u32 relative_id;
> +                       };

same comment about union, let's not add it and have two separate fields


> +                       __u32 expected_revision;
> +               } tcx;
>         };
>         size_t :0;
>  };
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index b89127471c6a..d7b6ff49f02e 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -133,6 +133,7 @@ static const char * const link_type_name[] = {
>         [BPF_LINK_TYPE_KPROBE_MULTI]            = "kprobe_multi",
>         [BPF_LINK_TYPE_STRUCT_OPS]              = "struct_ops",
>         [BPF_LINK_TYPE_NETFILTER]               = "netfilter",
> +       [BPF_LINK_TYPE_TCX]                     = "tcx",
>  };
>
>  static const char * const map_type_name[] = {
> @@ -11685,11 +11686,10 @@ static int attach_lsm(const struct bpf_program *prog, long cookie, struct bpf_li
>  }
>
>  static struct bpf_link *
> -bpf_program__attach_fd(const struct bpf_program *prog, int target_fd, int btf_id,
> -                      const char *target_name)
> +bpf_program__attach_fd_opts(const struct bpf_program *prog,
> +                           const struct bpf_link_create_opts *opts,
> +                           int target_fd, const char *target_name)

nit: please keep opts as the last argument

>  {
> -       DECLARE_LIBBPF_OPTS(bpf_link_create_opts, opts,
> -                           .target_btf_id = btf_id);
>         enum bpf_attach_type attach_type;
>         char errmsg[STRERR_BUFSIZE];
>         struct bpf_link *link;
> @@ -11707,7 +11707,7 @@ bpf_program__attach_fd(const struct bpf_program *prog, int target_fd, int btf_id
>         link->detach = &bpf_link__detach_fd;
>
>         attach_type = bpf_program__expected_attach_type(prog);
> -       link_fd = bpf_link_create(prog_fd, target_fd, attach_type, &opts);
> +       link_fd = bpf_link_create(prog_fd, target_fd, attach_type, opts);
>         if (link_fd < 0) {
>                 link_fd = -errno;
>                 free(link);
> @@ -11720,6 +11720,17 @@ bpf_program__attach_fd(const struct bpf_program *prog, int target_fd, int btf_id
>         return link;
>  }
>
> +static struct bpf_link *
> +bpf_program__attach_fd(const struct bpf_program *prog, int target_fd, int btf_id,
> +                      const char *target_name)
> +{
> +       LIBBPF_OPTS(bpf_link_create_opts, opts,
> +               .target_btf_id = btf_id,
> +       );
> +
> +       return bpf_program__attach_fd_opts(prog, &opts, target_fd, target_name);

it seems like the only user of btf_id is bpf_program__attach_freplace,
so I'd just inline this there, and for all other 4 cases let's just
pass NULL as options?

That means we don't really need bpf_program__attach_fd_opts() and can
just add opts to bpf_program__attach_fd(). We'll have shorter name.
BTW, given it's not exposed API, let's drop double underscore and call
it just bpf_program_attach_fd()?

> +}
> +
>  struct bpf_link *
>  bpf_program__attach_cgroup(const struct bpf_program *prog, int cgroup_fd)
>  {
> @@ -11738,6 +11749,29 @@ struct bpf_link *bpf_program__attach_xdp(const struct bpf_program *prog, int ifi
>         return bpf_program__attach_fd(prog, ifindex, 0, "xdp");
>  }
>
> +struct bpf_link *
> +bpf_program__attach_tcx_opts(const struct bpf_program *prog,
> +                            const struct bpf_tcx_opts *opts)

we don't have non-opts variant, so let's keep the name short (like we
did with bpf_program__attach_netlink): bpf_program__attach_tcx().

> +{
> +       LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
> +       int ifindex = OPTS_GET(opts, ifindex, 0);

let's not do OPTS_GET before we checked OPTS_VALID

> +
> +       if (!OPTS_VALID(opts, bpf_tcx_opts))
> +               return libbpf_err_ptr(-EINVAL);
> +       if (!ifindex) {
> +               pr_warn("prog '%s': target netdevice ifindex cannot be zero\n",
> +                       prog->name);
> +               return libbpf_err_ptr(-EINVAL);
> +       }
> +
> +       link_create_opts.tcx.expected_revision = OPTS_GET(opts, expected_revision, 0);
> +       link_create_opts.tcx.relative_fd = OPTS_GET(opts, relative_fd, 0);
> +       link_create_opts.flags = OPTS_GET(opts, flags, 0);
> +
> +       /* target_fd/target_ifindex use the same field in LINK_CREATE */
> +       return bpf_program__attach_fd_opts(prog, &link_create_opts, ifindex, "tc");
> +}
> +
>  struct bpf_link *bpf_program__attach_freplace(const struct bpf_program *prog,
>                                               int target_fd,
>                                               const char *attach_func_name)
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 754da73c643b..8ffba0f67c60 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -718,6 +718,23 @@ LIBBPF_API struct bpf_link *
>  bpf_program__attach_freplace(const struct bpf_program *prog,
>                              int target_fd, const char *attach_func_name);
>
> +struct bpf_tcx_opts {
> +       /* size of this struct, for forward/backward compatibility */
> +       size_t sz;
> +       int ifindex;
> +       __u32 flags;
> +       union {
> +               __u32 relative_fd;
> +               __u32 relative_id;
> +       };

same thing about not using unions here :)

> +       __u32 expected_revision;

and let's add `size_t :0;` to prevent compiler from leaving garbage
values in a padding at the end of the struct (once you drop union
there will be padding)

> +};
> +#define bpf_tcx_opts__last_field expected_revision
> +
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_tcx_opts(const struct bpf_program *prog,
> +                            const struct bpf_tcx_opts *opts);
> +
>  struct bpf_map;
>
>  LIBBPF_API struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map);
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index a29b90e9713c..f66b714512c2 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -396,4 +396,5 @@ LIBBPF_1.3.0 {
>         global:
>                 bpf_obj_pin_opts;
>                 bpf_prog_detach_opts;
> +               bpf_program__attach_tcx_opts;
>  } LIBBPF_1.2.0;
> --
> 2.34.1
>





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