Re: [PATCH net-next v3 02/14] net-timestamp: allow two features to work parallelly

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

Jason Xing wrote:
> On Wed, Oct 30, 2024 at 7:00 AM Martin KaFai Lau <martin.lau@linux.dev> wrote:
> >
> > On 10/28/24 4:05 AM, Jason Xing wrote:
> > > From: Jason Xing <kernelxing@tencent.com>
> > >
> > > This patch has introduced a separate sk_tsflags_bpf for bpf
> > > extension, which helps us let two feature work nearly at the
> > > same time.
> > >
> > > Each feature will finally take effect on skb_shinfo(skb)->tx_flags,
> > > say, tcp_tx_timestamp() for TCP or skb_setup_tx_timestamp() for
> > > other types, so in __skb_tstamp_tx() we are unable to know which
> > > feature is turned on, unless we check each feature's own socket
> > > flag field.
> > >
> > > Signed-off-by: Jason Xing <kernelxing@tencent.com>
> > > ---
> > >   include/net/sock.h |  1 +
> > >   net/core/skbuff.c  | 39 +++++++++++++++++++++++++++++++++++++++
> > >   2 files changed, 40 insertions(+)
> > >
> > > diff --git a/include/net/sock.h b/include/net/sock.h
> > > index 7464e9f9f47c..5384f1e49f5c 100644
> > > --- a/include/net/sock.h
> > > +++ b/include/net/sock.h
> > > @@ -445,6 +445,7 @@ struct sock {
> > >       u32                     sk_reserved_mem;
> > >       int                     sk_forward_alloc;
> > >       u32                     sk_tsflags;
> > > +     u32                     sk_tsflags_bpf;
> > >       __cacheline_group_end(sock_write_rxtx);
> > >
> > >       __cacheline_group_begin(sock_write_tx);
> > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> > > index 1cf8416f4123..39309f75e105 100644
> > > --- a/net/core/skbuff.c
> > > +++ b/net/core/skbuff.c
> > > @@ -5539,6 +5539,32 @@ void skb_complete_tx_timestamp(struct sk_buff *skb,
> > >   }
> > >   EXPORT_SYMBOL_GPL(skb_complete_tx_timestamp);
> > >
> > > +/* This function is used to test if application SO_TIMESTAMPING feature
> > > + * or bpf SO_TIMESTAMPING feature is loaded by checking its own socket flags.
> > > + */
> > > +static bool sk_tstamp_tx_flags(struct sock *sk, u32 tsflags, int tstype)
> > > +{
> > > +     u32 testflag;
> > > +
> > > +     switch (tstype) {
> > > +     case SCM_TSTAMP_SCHED:
> > > +             testflag = SOF_TIMESTAMPING_TX_SCHED;
> > > +             break;
> > > +     case SCM_TSTAMP_SND:
> > > +             testflag = SOF_TIMESTAMPING_TX_SOFTWARE;
> > > +             break;
> > > +     case SCM_TSTAMP_ACK:
> > > +             testflag = SOF_TIMESTAMPING_TX_ACK;
> > > +             break;
> > > +     default:
> > > +             return false;
> > > +     }
> > > +     if (tsflags & testflag)
> > > +             return true;
> > > +
> > > +     return false;
> > > +}
> > > +
> > >   static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
> > >                                const struct sk_buff *ack_skb,
> > >                                struct skb_shared_hwtstamps *hwtstamps,
> > > @@ -5549,6 +5575,9 @@ static void skb_tstamp_tx_output(struct sk_buff *orig_skb,
> > >       u32 tsflags;
> > >
> > >       tsflags = READ_ONCE(sk->sk_tsflags);
> > > +     if (!sk_tstamp_tx_flags(sk, tsflags, tstype))
> >
> > I still don't get this part since v2. How does it work with cmsg only
> > SOF_TIMESTAMPING_TX_*?
> >
> > I tried with "./txtimestamp -6 -c 1 -C -N -L ::1" and it does not return any tx
> > time stamp after this patch.
> >
> > I am likely missing something
> > or v2 concluded that this behavior change is acceptable?
> 
> Sorry, I submitted this series accidentally removing one important
> thing which is similar to what Vadim Fedorenko mentioned in the v1
> [1]:
> adding another member like sk_flags_bpf to handle the cmsg case.
> 
> Willem, would it be acceptable to add another field in struct sock to
> help us recognise the case where BPF and cmsg works parallelly?
> 
> [1]: https://lore.kernel.org/all/662873cb-a897-464e-bdb3-edf01363c3b2@linux.dev/

The current timestamp flags don't need a u32. Maybe just reserve a bit
for this purpose?