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From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: "Toke Høiland-Jørgensen" <toke@redhat.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	David Miller <davem@davemloft.net>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next v3 5/6] libbpf: Add bpf_get_link_xdp_info() function to get more XDP information
Date: Fri, 8 Nov 2019 16:51:03 -0800	[thread overview]
Message-ID: <CAEf4BzYvv6pCHygeNyOBE4MRtcLxE1XP4Ww+sxoaPgQw5i1Rjw@mail.gmail.com> (raw)
In-Reply-To: <157325766011.27401.5278664694085166014.stgit@toke.dk>

On Fri, Nov 8, 2019 at 4:01 PM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> From: Toke Høiland-Jørgensen <toke@redhat.com>
>
> Currently, libbpf only provides a function to get a single ID for the XDP
> program attached to the interface. However, it can be useful to get the
> full set of program IDs attached, along with the attachment mode, in one
> go. Add a new getter function to support this, using an extendible
> structure to carry the information. Express the old bpf_get_link_id()
> function in terms of the new function.
>
> Acked-by: David S. Miller <davem@davemloft.net>
> Acked-by: Song Liu <songliubraving@fb.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
> ---
>  tools/lib/bpf/libbpf.h   |   10 ++++++
>  tools/lib/bpf/libbpf.map |    1 +
>  tools/lib/bpf/netlink.c  |   82 ++++++++++++++++++++++++++++++----------------
>  3 files changed, 65 insertions(+), 28 deletions(-)
>

[...]

>
> -int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
> +int bpf_get_link_xdp_info(int ifindex, struct xdp_link_info *info,
> +                         size_t info_size, __u32 flags)
>  {
>         struct xdp_id_md xdp_id = {};
>         int sock, ret;
>         __u32 nl_pid;
>         __u32 mask;
>
> -       if (flags & ~XDP_FLAGS_MASK)
> +       if (flags & ~XDP_FLAGS_MASK || info_size < sizeof(*info))
>                 return -EINVAL;

Well, now it's backwards-incompatible: older program passes smaller
(but previously perfectly valid) sizeof(struct xdp_link_info) to newer
version of libbpf. This has to go both ways: smaller struct should be
supported as long as program doesn't request (using flags) something,
that can't be put into allowed space.

I know it's PITA to support this, but that's what we have to do for
forward/backward compatibility.

>
>         /* Check whether the single {HW,DRV,SKB} mode is set */
> @@ -274,14 +272,42 @@ int bpf_get_link_xdp_id(int ifindex, __u32 *prog_id, __u32 flags)
>         xdp_id.ifindex = ifindex;
>         xdp_id.flags = flags;
>
> -       ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_id, &xdp_id);
> -       if (!ret)
> -               *prog_id = xdp_id.id;
> +       ret = libbpf_nl_get_link(sock, nl_pid, get_xdp_info, &xdp_id);
> +       if (!ret) {
> +               memset(info, 0, info_size);
> +               memcpy(info, &xdp_id.info, min(info_size, sizeof(xdp_id.info)));

nit: memset above should start at info + min(info_size, sizeof(xdp_id.info))

> +       }
>
>         close(sock);
>         return ret;
>  }
>

[...]

  reply	other threads:[~2019-11-09  0:51 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-09  0:00 [PATCH bpf-next v3 0/6] libbpf: Fix pinning and error message bugs and add new getters Toke Høiland-Jørgensen
2019-11-09  0:00 ` [PATCH bpf-next v3 1/6] libbpf: Unpin auto-pinned maps if loading fails Toke Høiland-Jørgensen
2019-11-09  0:42   ` Andrii Nakryiko
2019-11-09  0:00 ` [PATCH bpf-next v3 2/6] selftests/bpf: Add tests for automatic map unpinning on load failure Toke Høiland-Jørgensen
2019-11-09  0:00 ` [PATCH bpf-next v3 3/6] libbpf: Propagate EPERM to caller on program load Toke Høiland-Jørgensen
2019-11-09  0:44   ` Andrii Nakryiko
2019-11-09  0:00 ` [PATCH bpf-next v3 4/6] libbpf: Use pr_warn() when printing netlink errors Toke Høiland-Jørgensen
2019-11-09  0:01 ` [PATCH bpf-next v3 5/6] libbpf: Add bpf_get_link_xdp_info() function to get more XDP information Toke Høiland-Jørgensen
2019-11-09  0:51   ` Andrii Nakryiko [this message]
2019-11-09 11:20     ` Toke Høiland-Jørgensen
2019-11-09 19:10       ` Andrii Nakryiko
2019-11-09 20:18         ` Toke Høiland-Jørgensen
2019-11-09  0:01 ` [PATCH bpf-next v3 6/6] libbpf: Add getter for program size Toke Høiland-Jørgensen

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