netdev - Re: [PATCH v5 1/5] net: timestamp: add helper returning skb's tx tstamp

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Message-ID: <6851983d94a2d_2e8c1b294bf@willemb.c.googlers.com.notmuch>
Date: Tue, 17 Jun 2025 12:30:53 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Pavel Begunkov <asml.silence@...il.com>, 
 io-uring@...r.kernel.org, 
 Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: asml.silence@...il.com, 
 netdev@...r.kernel.org, 
 Eric Dumazet <edumazet@...gle.com>, 
 Kuniyuki Iwashima <kuniyu@...zon.com>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Willem de Bruijn <willemb@...gle.com>, 
 "David S . Miller" <davem@...emloft.net>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Richard Cochran <richardcochran@...il.com>, 
 Stanislav Fomichev <sdf@...ichev.me>, 
 Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH v5 1/5] net: timestamp: add helper returning skb's tx
 tstamp

Willem de Bruijn wrote:
> Pavel Begunkov wrote:
> > Add a helper function skb_get_tx_timestamp() that returns a tx timestamp
> > associated with an error queue skb.
> > 
> > Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
> > ---
> >  include/net/sock.h |  4 ++++
> >  net/socket.c       | 46 ++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 50 insertions(+)
> > 
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index 92e7c1aae3cc..f5f5a9ad290b 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -2677,6 +2677,10 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
> >  void __sock_recv_wifi_status(struct msghdr *msg, struct sock *sk,
> >  			     struct sk_buff *skb);
> >  
> > +bool skb_has_tx_timestamp(struct sk_buff *skb, const struct sock *sk);
> > +int skb_get_tx_timestamp(struct sk_buff *skb, struct sock *sk,
> > +			 struct timespec64 *ts);
> > +
> >  static inline void
> >  sock_recv_timestamp(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
> >  {
> > diff --git a/net/socket.c b/net/socket.c
> > index 9a0e720f0859..2cab805943c0 100644
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -843,6 +843,52 @@ static void put_ts_pktinfo(struct msghdr *msg, struct sk_buff *skb,
> >  		 sizeof(ts_pktinfo), &ts_pktinfo);
> >  }
> >  
> > +bool skb_has_tx_timestamp(struct sk_buff *skb, const struct sock *sk)
> > +{
> 
> I forgot to ask earlier, and not a reason for a respin.
> 
> Is the only reason that skb is not const here skb_hwtstamps?
> 
> I can send a patch to make that container_of_const

Just to follow up.

The container_of_const is not applicable here. As skb_shared_info is
a (cast) pointer, into skb linear.

So even simpler, the skb can be const even if what its member points
to is not. This works fine.

-static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
+static inline struct skb_shared_hwtstamps *skb_hwtstamps(const struct sk_buff *skb)
 {
        return &skb_shinfo(skb)->hwtstamps;
 }

And same for skb_zcopy, skb_zcopy_init, skb_zcopy_set,
skb_zcopy_set_nouarg, skb_zcopy_is_nouarg, skb_zcopy_get_nouarg,
skb_zcopy_clear, __skb_zcopy_downgrade_managed,
skb_zcopy_downgrade_managed, skb_frag_ref and the ubuf_info_ops
complete and link callbacks.

But that's a lot of churn, especially if including ubuf_info
implementations like io_uring.

Not sure it's worth that.