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

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Message-ID: <07d408c8-c816-4997-ab87-1a6521d0bacd@gmail.com>
Date: Mon, 2 Jun 2025 10:57:11 +0100
From: Pavel Begunkov <asml.silence@...il.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 io-uring@...r.kernel.org, Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: 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 6/1/25 14:52, Willem de Bruijn wrote:
> 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?

Timestamps still need custom code, not like we can do a generic
implementation just by copying sock_extended_err to user. And then
it'll be a problem to fit it into completions, it's already tight
after placing the timeval directly into cqe, there are only
few bits left.

Either way, I guess it can be extended if there are more use cases,
or might be better introducing and new command to cover that and
share some of the handling.

...>> 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

will do

> 
>> +{
>> +	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.

Got it, I'll drop that chunk if you think it's fine. Thanks
for review

>> +	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.

I couldn't find a good way for doing that. There are rx checks in
every if, there is also pkt info handling nested. And
scm_timestamping_internal has 3 timeouts , so
__sock_recv_timestamp() would need to duplicate some checks to
choose the right place for the timeout or so.

-- 
Pavel Begunkov