On Fri, Nov 8, 2019 at 4:01 PM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> From: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> Signed-off-by: Toke Høiland-Jørgensen <toke@xxxxxxxxxx>
> ---
> 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;
> }
>
[...]
