netdev - Re: [PATCH v3 bpf-next 5/8] libbpf: add API to get XDP/XSK supported features

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Date:   Fri, 27 Jan 2023 15:38:53 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, davem@...emloft.net,
        kuba@...nel.org, hawk@...nel.org, pabeni@...hat.com,
        edumazet@...gle.com, toke@...hat.com, memxor@...il.com,
        alardam@...il.com, saeedm@...dia.com, anthony.l.nguyen@...el.com,
        gospo@...adcom.com, vladimir.oltean@....com, nbd@....name,
        john@...ozen.org, leon@...nel.org, simon.horman@...igine.com,
        aelior@...vell.com, christophe.jaillet@...adoo.fr,
        ecree.xilinx@...il.com, mst@...hat.com, bjorn@...nel.org,
        magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
        intel-wired-lan@...ts.osuosl.org, lorenzo.bianconi@...hat.com,
        martin.lau@...ux.dev
Subject: Re: [PATCH v3 bpf-next 5/8] libbpf: add API to get XDP/XSK supported features

On Thu, Jan 26, 2023 at 4:59 AM Lorenzo Bianconi <lorenzo@...nel.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@...il.com>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> Co-developed-by: Marek Majtyka <alardam@...il.com>
> Signed-off-by: Marek Majtyka <alardam@...il.com>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  tools/lib/bpf/libbpf.h  |  3 +-
>  tools/lib/bpf/netlink.c | 99 +++++++++++++++++++++++++++++++++++++++++
>  tools/lib/bpf/nlattr.h  | 12 +++++
>  3 files changed, 113 insertions(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 898db26e42e9..29cb7040fa77 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -982,9 +982,10 @@ struct bpf_xdp_query_opts {
>         __u32 hw_prog_id;       /* output */
>         __u32 skb_prog_id;      /* output */
>         __u8 attach_mode;       /* output */
> +       __u64 fflags;           /* output */
>         size_t :0;
>  };
> -#define bpf_xdp_query_opts__last_field attach_mode
> +#define bpf_xdp_query_opts__last_field fflags

is "fflags" an obvious name in this context? I'd expect
"feature_flags", especially that there are already "flags". Is saving
a few characters worth the confusion?


>
>  LIBBPF_API int bpf_xdp_attach(int ifindex, int prog_fd, __u32 flags,
>                               const struct bpf_xdp_attach_opts *opts);
> diff --git a/tools/lib/bpf/netlink.c b/tools/lib/bpf/netlink.c
> index d2468a04a6c3..674e4d61e67e 100644
> --- a/tools/lib/bpf/netlink.c
> +++ b/tools/lib/bpf/netlink.c
> @@ -9,6 +9,7 @@
>  #include <linux/if_ether.h>
>  #include <linux/pkt_cls.h>
>  #include <linux/rtnetlink.h>
> +#include <linux/netdev.h>
>  #include <sys/socket.h>
>  #include <errno.h>
>  #include <time.h>
> @@ -39,6 +40,12 @@ struct xdp_id_md {
>         int ifindex;
>         __u32 flags;
>         struct xdp_link_info info;
> +       __u64 fflags;
> +};
> +
> +struct xdp_features_md {
> +       int ifindex;
> +       __u64 flags;
>  };
>
>  static int libbpf_netlink_open(__u32 *nl_pid, int proto)

[...]

>  int bpf_xdp_query(int ifindex, int xdp_flags, struct bpf_xdp_query_opts *opts)
>  {
>         struct libbpf_nla_req req = {
> @@ -393,6 +460,38 @@ 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, fflags)) {

maybe invert condition, return early, reduce nesting of the following code?

> +               struct xdp_features_md md = {
> +                       .ifindex = ifindex,
> +               };
> +               __u16 id;
> +
> +               err = libbpf_netlink_resolve_genl_family_id("netdev",
> +                                                           sizeof("netdev"),
> +                                                           &id);

nit: if it fits under 100 characters, let's leave it on a single line

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

[...]