netdev - Re: [RFC bpf-next 6/8] libbpf: add API to get XDP/XSK supported features

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Date:   Tue, 10 Jan 2023 18:26:45 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
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, grygorii.strashko@...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
Subject: Re: [RFC bpf-next 6/8] libbpf: add API to get XDP/XSK supported
 features

> On Mon, Dec 19, 2022 at 7:42 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> >
> > From: Kumar Kartikeya Dwivedi <memxor@...il.com>
> >
> > Add functions to get XDP/XSK supported function of netdev over route
> > netlink interface. These functions provide functionalities that are
> > going to be used in upcoming change.
> >
> > The newly added bpf_xdp_query_features takes a fflags_cnt parameter,
> > which denotes the number of elements in the output fflags array. This
> > must be at least 1 and maybe greater than XDP_FEATURES_WORDS. The
> > function only writes to words which is min of fflags_cnt and
> > XDP_FEATURES_WORDS.
> >
> > Co-developed-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > Co-developed-by: Marek Majtyka <alardam@...il.com>
> > Signed-off-by: Marek Majtyka <alardam@...il.com>
> > Signed-off-by: Kumar Kartikeya Dwivedi <memxor@...il.com>
> > ---
> >  tools/lib/bpf/libbpf.h   |  1 +
> >  tools/lib/bpf/libbpf.map |  1 +
> >  tools/lib/bpf/netlink.c  | 62 ++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 64 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> > index eee883f007f9..9d102eb5007e 100644
> > --- a/tools/lib/bpf/libbpf.h
> > +++ b/tools/lib/bpf/libbpf.h
> > @@ -967,6 +967,7 @@ LIBBPF_API int bpf_xdp_detach(int ifindex, __u32 flags,
> >                               const struct bpf_xdp_attach_opts *opts);
> >  LIBBPF_API int bpf_xdp_query(int ifindex, int flags, struct bpf_xdp_query_opts *opts);
> >  LIBBPF_API int bpf_xdp_query_id(int ifindex, int flags, __u32 *prog_id);
> > +LIBBPF_API int bpf_xdp_query_features(int ifindex, __u32 *fflags, __u32 *fflags_cnt);
> 
> no need to add new API, just extend bpf_xdp_query()?

Hi Andrii,

AFAIK libbpf supports just NETLINK_ROUTE protocol. In order to connect with the
genl family code shared by Jakub we need to add NETLINK_GENERIC protocol support
to libbf. Is it ok to introduce a libmnl or libnl dependency in libbpf or do you
prefer to add open code to just what we need?
I guess we should have a dedicated API to dump xdp features in this case since
all the other code relies on NETLINK_ROUTE protocol. What do you think?

Regards,
Lorenzo

> 
> >
> >  /* TC related API */
> >  enum bpf_tc_attach_point {
> > diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> > index 71bf5691a689..9c2abb58fa4b 100644
> > --- a/tools/lib/bpf/libbpf.map
> > +++ b/tools/lib/bpf/libbpf.map
> > @@ -362,6 +362,7 @@ LIBBPF_1.0.0 {
> >                 bpf_program__set_autoattach;
> >                 btf__add_enum64;
> >                 btf__add_enum64_value;
> > +               bpf_xdp_query_features;
> >                 libbpf_bpf_attach_type_str;
> >                 libbpf_bpf_link_type_str;
> >                 libbpf_bpf_map_type_str;
> 
> [...]

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