netdev - Re: [RFC v2 net-next 03/12] libbpf: api for getting/setting link xdp options

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Date:   Fri, 3 Jan 2020 20:04:46 +0900
From:   Prashant Bhole <prashantbhole.linux@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jason Wang <jasowang@...hat.com>,
        David Ahern <dsahern@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        John Fastabend <john.fastabend@...il.com>,
        Toshiaki Makita <toshiaki.makita1@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [RFC v2 net-next 03/12] libbpf: api for getting/setting link xdp
 options



On 12/30/2019 1:49 PM, Andrii Nakryiko wrote:
> On Wed, Dec 25, 2019 at 6:34 PM Prashant Bhole
> <prashantbhole.linux@...il.com> wrote:
>>
>> This patch introduces and uses new APIs:
>>
>> struct bpf_link_xdp_opts {
>>          struct xdp_link_info *link_info;
>>          size_t link_info_sz;
>>          __u32 flags;
>>          __u32 prog_id;
>>          int prog_fd;
>> };
> 
> Please see the usage of DECLARE_LIBBPF_OPTS and OPTS_VALID/OPTS_GET
> (e.g., in bpf_object__open_file). This also seems like a rather
> low-level API, so might be more appropriate to follow the naming of
> low-level API in bpf.h (see Andrey Ignatov's recent
> bpf_prog_attach_xattr() changes).
> 
> As is this is not backwards/forward compatible, unless you use
> LIBBPF_OPTS approach (that's what Alexei meant).

Got it.

> 
> 
>>
>> enum bpf_link_cmd {
>>          BPF_LINK_GET_XDP_INFO,
>>          BPF_LINK_GET_XDP_ID,
>>          BPF_LINK_SET_XDP_FD,
>> };
>>
>> int bpf_get_link_opts(int ifindex, struct bpf_link_xdp_opts *opts,
>>                        enum bpf_link_cmd cmd);
>> int bpf_set_link_opts(int ifindex, struct bpf_link_xdp_opts *opts,
>>                        enum bpf_link_cmd cmd);
>>
>> The operations performed by these two functions are equivalent to
>> existing APIs.
>>
>> BPF_LINK_GET_XDP_ID equivalent to bpf_get_link_xdp_id()
>> BPF_LINK_SET_XDP_FD equivalent to bpf_set_link_xdp_fd()
>> BPF_LINK_GET_XDP_INFO equivalent to bpf_get_link_xdp_info()
>>
>> It will be easy to extend this API by adding members in struct
>> bpf_link_xdp_opts and adding different operations. Next patch
>> will extend this API to set XDP program in the tx path.
> 
> Not really, and this has been extensively discussed previously. One of
> the problems is old user code linked against newer libbpf version
> (shared library). New libbpf will assume struct with more fields,
> while old user code will provide too short struct. That's why all the
> LIBBPF_OPTS stuff.

Got it. Thanks for reviewing.

Prashant

> 
>>
>> Signed-off-by: Prashant Bhole <prashantbhole.linux@...il.com>
>> ---
>>   tools/lib/bpf/libbpf.h   | 36 +++++++++++++++++++
>>   tools/lib/bpf/libbpf.map |  2 ++
>>   tools/lib/bpf/netlink.c  | 77 ++++++++++++++++++++++++++++++++++++----
>>   3 files changed, 109 insertions(+), 6 deletions(-)
>>
> 
> [...]
>