On Tue, Oct 8, 2019 at 9:29 PM John Fastabend <john.fastabend@xxxxxxxxx> wrote:
>
> Magnus Karlsson wrote:
> > When the need_wakeup flag was added to AF_XDP, the format of the
> > XDP_MMAP_OFFSETS getsockopt was extended. Code was added to the kernel
> > to take care of compatibility issues arrising from running
> > applications using any of the two formats. However, libbpf was not
> > extended to take care of the case when the application/libbpf uses the
> > new format but the kernel only supports the old format. This patch
> > adds support in libbpf for parsing the old format, before the
> > need_wakeup flag was added, and emulating a set of static need_wakeup
> > flags that will always work for the application.
> >
> > Fixes: a4500432c2587cb2a ("libbpf: add support for need_wakeup flag in AF_XDP part")
> > Reported-by: Eloy Degen <degeneloy@xxxxxxxxx>
> > Signed-off-by: Magnus Karlsson <magnus.karlsson@xxxxxxxxx>
> > ---
> > tools/lib/bpf/xsk.c | 109 +++++++++++++++++++++++++++++++++++++---------------
> > 1 file changed, 78 insertions(+), 31 deletions(-)
> >
> > diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> > index a902838..46f9687 100644
> > --- a/tools/lib/bpf/xsk.c
> > +++ b/tools/lib/bpf/xsk.c
> > @@ -44,6 +44,25 @@
> > #define PF_XDP AF_XDP
> > #endif
> >
> > +#define is_mmap_offsets_v1(optlen) \
> > + ((optlen) == sizeof(struct xdp_mmap_offsets_v1))
> > +
> > +#define get_prod_off(ring) \
> > + (is_mmap_offsets_v1(optlen) ? \
> > + ((struct xdp_mmap_offsets_v1 *)&off)->ring.producer : \
> > + off.ring.producer)
> > +#define get_cons_off(ring) \
> > + (is_mmap_offsets_v1(optlen) ? \
> > + ((struct xdp_mmap_offsets_v1 *)&off)->ring.consumer : \
> > + off.ring.consumer)
> > +#define get_desc_off(ring) \
> > + (is_mmap_offsets_v1(optlen) ? \
> > + ((struct xdp_mmap_offsets_v1 *)&off)->ring.desc : off.ring.desc)
> > +#define get_flags_off(ring) \
> > + (is_mmap_offsets_v1(optlen) ? \
> > + ((struct xdp_mmap_offsets_v1 *)&off)->ring.consumer + sizeof(u32) : \
> > + off.ring.flags)
> > +
>
> It seems the only thing added was flags right? If so seems we
> only need the last one there, get_flags_off(). I think it would
> be a bit cleaner to just use the macros where its actually
> needed IMO.
The flag is indeed added to the end of struct xdp_ring_offsets, but
this struct is replicated four times in the struct xdp_mmap_offsets,
so the added flags are present four time there at different offsets.
This means that 3 out of the 4 prod, cons and desc variables are
located at different offsets from the original. Do not know how I can
get rid of these macros in this case. But it might just be me not
seeing it, of course :-).
Thanks: Magnus
> Thanks,
> John
