Re: [PATCH net-next 7/9] net-timestamp: open gate for bpf_setsockopt

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Jason Xing wrote:
> On Wed, Oct 9, 2024 at 3:19 PM Martin KaFai Lau <martin.lau@linux.dev> wrote:
> >
> > On 10/8/24 2:51 AM, Jason Xing wrote:
> > > From: Jason Xing <kernelxing@tencent.com>
> > >
> > > Now we allow users to set tsflags through bpf_setsockopt. What I
> > > want to do is passing SOF_TIMESTAMPING_RX_SOFTWARE flag, so that
> > > we can generate rx timestamps the moment the skb traverses through
> > > driver.
> > >
> > > Here is an example:
> > >
> > > case BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB:
> > > case BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB:
> > >       sock_opt = SOF_TIMESTAMPING_RX_SOFTWARE;
> > >       bpf_setsockopt(skops, SOL_SOCKET, SO_TIMESTAMPING,
> > >                      &sock_opt, sizeof(sock_opt));
> > >       break;
> > >
> > > In this way, we can use bpf program that help us generate and report
> > > rx timestamp.
> > >
> > > Signed-off-by: Jason Xing <kernelxing@tencent.com>
> > > ---
> > >   net/core/filter.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/net/core/filter.c b/net/core/filter.c
> > > index bd0d08bf76bb..9ce99d320571 100644
> > > --- a/net/core/filter.c
> > > +++ b/net/core/filter.c
> > > @@ -5225,6 +5225,9 @@ static int sol_socket_sockopt(struct sock *sk, int optname,
> > >               break;
> > >       case SO_BINDTODEVICE:
> > >               break;
> > > +     case SO_TIMESTAMPING_NEW:
> > > +     case SO_TIMESTAMPING_OLD:
> >
> > I believe this change was proposed before. It will change the user expectation
> > on the sk_error_queue. It needs some bits/fields/knobs for bpf. I think this
> > point is similar to other's earlier comments in this thread.
> 
> Thanks for your reply.
> 
> After seeing what you mentioned, I searched through the mailing list
> and found one [1] which was designed to fetch hardware timestamps.
> 
> [1]：https://lore.kernel.org/bpf/51fd5249-140a-4f1b-b20e-703f159e88a3@linux.dev/T/
> 
> >
> > I only have a chance to briefly look at it. I think it is useful. This
> > bpf/timestamp feature request has come up before.
> 
> At the very beginning, I had no intention to use bpf_setsockopt() to
> retrieve the rx timestamp because it will override sk_tsflags, but I
> cannot implement a good way like what I did to tx path: only setting
> skb's field. I'm not sure if this override behaviour is acceptable, so
> I post it to know what the bpf experts' suggestions are.
> 
> >
> > A high level comment. The current timestamp should work for non tcp sock? The
> > bpf/timestamp solution should be able to also.
> 
> For now, it only supports TCP proto. I would like to quickly implement
> a framework which is also suitable for other protos. TCP is just a
> start point.
> 
> >
> > sockops is tcp centric. From looking at patch 9 that needs to initialize 4 args,
> > this interface feels old and not sure we want to extend to other sock types.
> > This needs some thoughts.
> 
> For me, I have interests to extend to other sock types. But I'm
> supposed to ask Willem's opinion first.
> 
> +Willem de Bruijn Do you want this bpf extension feature to extend to
> other protos?

There would likely be users for other protocols too, just like
SO_TIMESTAMPING. Though TCP is probably the most widely used case by
far.