netdev - Re: [PATCH bpf-next] libbpf: remove zc variable as it is not used

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Message-ID: <CAJ8uoz1qhaHwebmjOOS9xfJe93Eq0v=SXhQUnjHv7imVL3ONsQ@mail.gmail.com>
Date:   Mon, 19 Aug 2019 09:35:17 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Jonathan Lemon <jonathan.lemon@...il.com>,
        Yonghong Song <yhs@...com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] libbpf: remove zc variable as it is not used

On Mon, Aug 19, 2019 at 8:47 AM Maxim Mikityanskiy <maximmi@...lanox.com> wrote:
>
> On 2019-08-19 09:35, Magnus Karlsson wrote:
> > On Sat, Aug 17, 2019 at 12:02 AM Jonathan Lemon
> > <jonathan.lemon@...il.com> wrote:
> >>
> >>
> >>
> >> On 16 Aug 2019, at 8:37, Yonghong Song wrote:
> >>
> >>> On 8/16/19 3:26 AM, Magnus Karlsson wrote:
> >>>> The zc is not used in the xsk part of libbpf, so let us remove it.
> >>>> Not
> >>>> good to have dead code lying around.
> >>>>
> >>>> Signed-off-by: Magnus Karlsson <magnus.karlsson@...el.com>
> >>>> Reported-by: Yonghong Song <yhs@...com> > ---
> >>>>    tools/lib/bpf/xsk.c | 3 ---
> >>>>    1 file changed, 3 deletions(-)
> >>>>
> >>>> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> >>>> index 680e630..9687da9 100644
> >>>> --- a/tools/lib/bpf/xsk.c
> >>>> +++ b/tools/lib/bpf/xsk.c
> >>>> @@ -65,7 +65,6 @@ struct xsk_socket {
> >>>>       int xsks_map_fd;
> >>>>       __u32 queue_id;
> >>>>       char ifname[IFNAMSIZ];
> >>>> -    bool zc;
> >>>>    };
> >>>>
> >>>>    struct xsk_nl_info {
> >>>> @@ -608,8 +607,6 @@ int xsk_socket__create(struct xsk_socket
> >>>> **xsk_ptr, const char *ifname,
> >>>>               goto out_mmap_tx;
> >>>>       }
> >>>>
> >>>> -    xsk->zc = opts.flags & XDP_OPTIONS_ZEROCOPY;
> >>>
> >>> Since opts.flags usage is removed. Do you think it makes sense to
> >>> remove
> >>>           optlen = sizeof(opts);
> >>>           err = getsockopt(xsk->fd, SOL_XDP, XDP_OPTIONS, &opts,
> >>> &optlen);
> >>>           if (err) {
> >>>                   err = -errno;
> >>>                   goto out_mmap_tx;
> >>>           }
> >>> as well since nobody then uses opts?
> >>
> >> IIRC, this was added specifically in
> >> 2761ed4b6e192820760d5ba913834b2ba05fd08c
> >> so that userland code could know whether the socket was operating in
> >> zero-copy
> >> mode or not.
> >
> > Thanks for reminding me Jonathan.
> >
> > Roping in Maxim here since he wrote the patch. Was this something you
> > planned on using but the functionality that needed it was removed? The
> > patch set did go through a number of changes in the libbpf area, if I
> > remember correctly.
> >
> > There are two options: either we remove it, or we add an interface in
> > xsk.h so that people can use it. I vote for the latter since I think
> > it could be useful. The sample app could use it at least :-).
>
> +1, let's expose it and make xdpsock read and print it. I added this
> flag to libbpf when I added the ability to query it from the kernel, but
> I didn't pay attention that struct xsk_socket was private to libbpf, and
> xsk->zc couldn't be accessed externally.

Good. I will then add it.

Please discard this patch. I will add this interface in a new patch.

/Magnus

> > /Magnus
> >
> >> --
> >> Jonathan
>