netdev - Re: [PATCH net-next v3 02/14] net-timestamp: allow two features to work parallelly

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Message-ID: <672a2bdff1896_791352942b@willemb.c.googlers.com.notmuch>
Date: Tue, 05 Nov 2024 09:29:51 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 Jason Xing <kerneljasonxing@...il.com>
Cc: willemb@...gle.com, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 andrii@...nel.org, 
 eddyz87@...il.com, 
 song@...nel.org, 
 yonghong.song@...ux.dev, 
 john.fastabend@...il.com, 
 kpsingh@...nel.org, 
 sdf@...ichev.me, 
 haoluo@...gle.com, 
 jolsa@...nel.org, 
 shuah@...nel.org, 
 ykolal@...com, 
 bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v3 02/14] net-timestamp: allow two features to
 work parallelly

Martin KaFai Lau wrote:
> On 11/1/24 6:32 AM, Willem de Bruijn wrote:
> >> In udp/raw/..., I don't know how likely is the user space having "cork->tx_flags
> >> & SKBTX_ANY_TSTAMP" set but has neither "READ_ONCE(sk->sk_tsflags) &
> >> SOF_TIMESTAMPING_OPT_ID" nor "cork->flags & IPCORK_TS_OPT_ID" set.
> > This is not something to rely on. OPT_ID was added relatively recently.
> > Older applications, or any that just use the most straightforward API,
> > will not set this.
> 
> Good point that the OPT_ID per cmsg is very new.
> 
> The datagram support on SOF_TIMESTAMPING_OPT_ID in sk->sk_tsflags had
> been there for quite some time now. Is it a safe assumption that
> most applications doing udp tx timestamping should have
> the SOF_TIMESTAMPING_OPT_ID set to be useful?

I don't think so.

The very first open source code I happen to look at, github.com/ptpd,
already sets SO_TIMESTAMPING without OPT_ID.