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

[Stanislav Fomichev <stfomichev@gmail.com>]

On 05/30, Stanislav Fomichev wrote:
> On 05/30, Pavel Begunkov wrote:
> > Add a helper function skb_get_tx_timestamp() that returns a tx timestamp
> > associated with an skb from an queue queue.
> > 
> > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
> > ---
> >  include/net/sock.h |  4 ++++
> >  net/socket.c       | 49 ++++++++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 53 insertions(+)
> > 
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index 92e7c1aae3cc..b0493e82b6e3 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, struct sock *sk);
> > +bool 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..d1dc8ab28e46 100644
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -843,6 +843,55 @@ 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, struct sock *sk)
> > +{
> > +	u32 tsflags = READ_ONCE(sk->sk_tsflags);
> > +	struct sock_exterr_skb *serr = SKB_EXT_ERR(skb);
> > +
> > +	if (serr->ee.ee_errno != ENOMSG ||
> > +	   serr->ee.ee_origin != SO_EE_ORIGIN_TIMESTAMPING)
> > +		return false;
> > +
> > +	/* software time stamp available and wanted */
> > +	if ((tsflags & SOF_TIMESTAMPING_SOFTWARE) && skb->tstamp)
> > +		return true;
> > +	/* hardware time stamps available and wanted */
> > +	return (tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
> > +		skb_hwtstamps(skb)->hwtstamp;
> > +}
> > +
> > +bool skb_get_tx_timestamp(struct sk_buff *skb, struct sock *sk,
> > +			  struct timespec64 *ts)
> > +{
> > +	u32 tsflags = READ_ONCE(sk->sk_tsflags);
> > +	bool false_tstamp = false;
> > +	ktime_t hwtstamp;
> > +	int if_index = 0;
> > +
> 
> [..]
> 
> > +	if (sock_flag(sk, SOCK_RCVTSTAMP) && skb->tstamp == 0) {
> > +		__net_timestamp(skb);
> > +		false_tstamp = true;
> > +	}
> 
> The place it was copy-pasted from (__sock_recv_timestamp) has a comment
> about a race between packet rx and enabling the timestamp. Does the same
> race happen here? Worth keeping the comment?

Or maybe you don't need this case at all? Since you're skipping the
tstamp == 0 cases anyway down below... Pass 'false' to skb_is_swtx_tstamp
instead?