Re: [PATCH v5 bpf-next 5/8] libbpf: add API to get XDP/XSK supported features

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

On Wed, Feb 1, 2023 at 2:25 AM Lorenzo Bianconi <lorenzo@kernel.org> wrote:
>
> Extend bpf_xdp_query routine in order to get XDP/XSK supported features
> of netdev over route netlink interface.
> Extend libbpf netlink implementation in order to support netlink_generic
> protocol.
>
> Co-developed-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> Co-developed-by: Marek Majtyka <alardam@gmail.com>
> Signed-off-by: Marek Majtyka <alardam@gmail.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
> ---
>  tools/lib/bpf/libbpf.h  |  3 +-
>  tools/lib/bpf/netlink.c | 96 +++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/nlattr.h  | 12 ++++++
>  3 files changed, 110 insertions(+), 1 deletion(-)
>

[...]

> @@ -366,6 +433,10 @@ int bpf_xdp_query(int ifindex, int xdp_flags, struct bpf_xdp_query_opts *opts)
>                 .ifinfo.ifi_family = AF_PACKET,
>         };
>         struct xdp_id_md xdp_id = {};
> +       struct xdp_features_md md = {
> +               .ifindex = ifindex,
> +       };
> +       __u16 id;
>         int err;
>
>         if (!OPTS_VALID(opts, bpf_xdp_query_opts))
> @@ -393,6 +464,31 @@ int bpf_xdp_query(int ifindex, int xdp_flags, struct bpf_xdp_query_opts *opts)
>         OPTS_SET(opts, skb_prog_id, xdp_id.info.skb_prog_id);
>         OPTS_SET(opts, attach_mode, xdp_id.info.attach_mode);
>
> +       if (!OPTS_HAS(opts, feature_flags))
> +               return 0;
> +
> +       err = libbpf_netlink_resolve_genl_family_id("netdev", sizeof("netdev"), &id);
> +       if (err < 0)
> +               return libbpf_err(err);
> +
> +       memset(&req, 0, sizeof(req));
> +       req.nh.nlmsg_len = NLMSG_LENGTH(GENL_HDRLEN);
> +       req.nh.nlmsg_flags = NLM_F_REQUEST;
> +       req.nh.nlmsg_type = id;
> +       req.gnl.cmd = NETDEV_CMD_DEV_GET;
> +       req.gnl.version = 2;
> +
> +       err = nlattr_add(&req, NETDEV_A_DEV_IFINDEX, &ifindex, sizeof(ifindex));
> +       if (err < 0)
> +               return err;

just noticed this, we need to use libbpf_err(err) here like in other
error cases to set errno properly. Can you please send a follow up?

> +
> +       err = libbpf_netlink_send_recv(&req, NETLINK_GENERIC,
> +                                      parse_xdp_features, NULL, &md);
> +       if (err)
> +               return libbpf_err(err);
> +
> +       opts->feature_flags = md.flags;
> +
>         return 0;
>  }
>

[...]