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

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Message-ID: <683c5b38ed614_232d4429431@willemb.c.googlers.com.notmuch>
Date: Sun, 01 Jun 2025 09:52:56 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: 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>
Subject: Re: [PATCH 1/5] net: timestamp: add helper returning skb's tx tstamp

Pavel Begunkov wrote:
> Add a helper function skb_get_tx_timestamp() that returns a tx timestamp
> associated with an skb from an queue queue.

Just curious: why a timestamp specific operation, rather than a
general error queue report?
 
> Signed-off-by: Pavel Begunkov <asml.silence@...il.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)

Here and elsewhere: consider const pointers where possible

> +{
> +	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;
> +	}

This is for SO_TIMESTAMP, not SO_TIMESTAMPING, and intended in the
receive path only, where net_enable_timestamp may be too late for
initial packets.

> +	if ((tsflags & SOF_TIMESTAMPING_SOFTWARE) &&
> +	    ktime_to_timespec64_cond(skb->tstamp, ts))
> +		return true;
> +
> +	if (!(tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) ||
> +	    skb_is_swtx_tstamp(skb, false_tstamp))
> +		return false;
> +
> +	if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_NETDEV)
> +		hwtstamp = get_timestamp(sk, skb, &if_index);
> +	else
> +		hwtstamp = skb_hwtstamps(skb)->hwtstamp;
> +
> +	if (tsflags & SOF_TIMESTAMPING_BIND_PHC)
> +		hwtstamp = ptp_convert_timestamp(&hwtstamp,
> +						READ_ONCE(sk->sk_bind_phc));
> +	return ktime_to_timespec64_cond(hwtstamp, ts);

This duplicates code in __sock_recv_timestamp. Perhaps worth a helper.

> +}
> +
>  /*
>   * called from sock_recv_timestamp() if sock_flag(sk, SOCK_RCVTSTAMP)
>   */
> -- 
> 2.49.0
>