netdev - Re: [PATCH bpf-next v11 08/12] bpf: add BPF_SOCK_OPS_TS_HW_OPT

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Message-ID: <67b0ad8819948_36e344294a7@willemb.c.googlers.com.notmuch>
Date: Sat, 15 Feb 2025 10:06:48 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 willemdebruijn.kernel@...il.com, 
 willemb@...gle.com, 
 ast@...nel.org, 
 daniel@...earbox.net, 
 andrii@...nel.org, 
 martin.lau@...ux.dev, 
 eddyz87@...il.com, 
 song@...nel.org, 
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 john.fastabend@...il.com, 
 kpsingh@...nel.org, 
 sdf@...ichev.me, 
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 horms@...nel.org
Cc: bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH bpf-next v11 08/12] bpf: add BPF_SOCK_OPS_TS_HW_OPT_CB
 callback

Jason Xing wrote:
> Support hw SCM_TSTAMP_SND case for bpf timestamping.
> 
> Add a new sock_ops callback, BPF_SOCK_OPS_TS_HW_OPT_CB. This
> callback will occur at the same timestamping point as the user
> space's hardware SCM_TSTAMP_SND. The BPF program can use it to
> get the same SCM_TSTAMP_SND timestamp without modifying the
> user-space application.
> 
> To avoid increasing the code complexity, replace SKBTX_HW_TSTAMP
> with SKBTX_HW_TSTAMP_NOBPF instead of changing numerous callers
> from driver side using SKBTX_HW_TSTAMP. The new definition of
> SKBTX_HW_TSTAMP means the combination tests of socket timestamping
> and bpf timestamping. After this patch, drivers can work under the
> bpf timestamping.
> 
> Considering some drivers doesn't assign the skb with hardware
> timestamp,

This is not for a real technical limitation, like the skb perhaps
being cloned or shared?

> this patch do the assignment and then BPF program
> can acquire the hwstamp from skb directly.

If the above is not the case and it is safe to write to the skb_shinfo,
and only if respinning anyway, grammar:

s/doesn't/don't/
s/do/does/