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

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Message-ID: <aDn1fV8D2G90mztp@mini-arch>
Date: Fri, 30 May 2025 11:14:21 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Pavel Begunkov <asml.silence@...il.com>
Cc: io-uring@...r.kernel.org, Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
	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

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@...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)
> +{
> +	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?