Subject: Re: [xdp-hints] Re: [PATCH bpf-next 05/11] veth: Support rx timestamp metadata for xdp

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Tue, 15 Nov 2022 23:46:02 +0100

Stanislav Fomichev <[email-masked]> writes:

> On Tue, Nov 15, 2022 at 8:17 AM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> Stanislav Fomichev <[email-masked]> writes:
>>
>> > The goal is to enable end-to-end testing of the metadata
>> > for AF_XDP. Current rx_timestamp kfunc returns current
>> > time which should be enough to exercise this new functionality.
>> >
>> > Cc: John Fastabend <[email-masked]>
>> > Cc: David Ahern <[email-masked]>
>> > Cc: Martin KaFai Lau <[email-masked]>
>> > Cc: Jakub Kicinski <[email-masked]>
>> > Cc: Willem de Bruijn <[email-masked]>
>> > Cc: Jesper Dangaard Brouer <[email-masked]>
>> > Cc: Anatoly Burakov <[email-masked]>
>> > Cc: Alexander Lobakin <[email-masked]>
>> > Cc: Magnus Karlsson <[email-masked]>
>> > Cc: Maryam Tahhan <[email-masked]>
>> > Cc: [email-masked]
>> > Cc: [email-masked]
>> > Signed-off-by: Stanislav Fomichev <[email-masked]>
>> > ---
>> >  drivers/net/veth.c | 14 ++++++++++++++
>> >  1 file changed, 14 insertions(+)
>> >
>> > diff --git a/drivers/net/veth.c b/drivers/net/veth.c
>> > index 2a4592780141..c626580a2294 100644
>> > --- a/drivers/net/veth.c
>> > +++ b/drivers/net/veth.c
>> > @@ -25,6 +25,7 @@
>> >  #include <linux/filter.h>
>> >  #include <linux/ptr_ring.h>
>> >  #include <linux/bpf_trace.h>
>> > +#include <linux/bpf_patch.h>
>> >  #include <linux/net_tstamp.h>
>> >
>> >  #define DRV_NAME     "veth"
>> > @@ -1659,6 +1660,18 @@ static int veth_xdp(struct net_device *dev, struct netdev_bpf *xdp)
>> >       }
>> >  }
>> >
>> > +static void veth_unroll_kfunc(const struct bpf_prog *prog, u32 func_id,
>> > +                           struct bpf_patch *patch)
>> > +{
>> > +     if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP_SUPPORTED)) {
>> > +             /* return true; */
>> > +             bpf_patch_append(patch, BPF_MOV64_IMM(BPF_REG_0, 1));
>> > +     } else if (func_id == xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_TIMESTAMP)) {
>> > +             /* return ktime_get_mono_fast_ns(); */
>> > +             bpf_patch_append(patch, BPF_EMIT_CALL(ktime_get_mono_fast_ns));
>> > +     }
>> > +}
>>
>> So these look reasonable enough, but would be good to see some examples
>> of kfunc implementations that don't just BPF_CALL to a kernel function
>> (with those helper wrappers we were discussing before).
>
> Let's maybe add them if/when needed as we add more metadata support?
> xdp_metadata_export_to_skb has an example, and rfc 1/2 have more
> examples, so it shouldn't be a problem to resurrect them back at some
> point?

Well, the reason I asked for them is that I think having to maintain the
BPF code generation in the drivers is probably the biggest drawback of
the kfunc approach, so it would be good to be relatively sure that we
can manage that complexity (via helpers) before we commit to this :)

-Toke