On Sat, Nov 9, 2019 at 3:20 AM Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
> Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> writes:
>
> > 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.
>
> But there's nothing to be backwards-compatible with? I get that *when*
> we extend the size of xdp_link_info, we should still accept the old,
> smaller size. But in this case that cannot happen as we're only just
> introducing this now?
This seems like a shifting burden to next person that will have to
extend this, but ok, fine by me.
>
> -Toke
