linux-kernel - Re: [PATCH bpf-next] bpf: Allow setting SO_TIMESTAMPING* with bpf

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Message-ID: <51fd5249-140a-4f1b-b20e-703f159e88a3@linux.dev>
Date: Tue, 16 Jan 2024 23:33:39 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jörn-Thorben Hinz <j-t.hinz@...mni.tu-berlin.de>
Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Andrii Nakryiko <andrii@...nel.org>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Shuah Khan <shuah@...nel.org>, Arnd Bergmann <arnd@...db.de>,
 Deepa Dinamani <deepa.kernel@...il.com>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: Allow setting SO_TIMESTAMPING* with
 bpf_setsockopt()

On 1/16/24 7:17 AM, Willem de Bruijn wrote:
> Jörn-Thorben Hinz wrote:
>> A BPF application, e.g., a TCP congestion control, might benefit from or
>> even require precise (=hardware) packet timestamps. These timestamps are
>> already available through __sk_buff.hwtstamp and
>> bpf_sock_ops.skb_hwtstamp, but could not be requested: BPF programs were
>> not allowed to set SO_TIMESTAMPING* on sockets.

This patch only uses the SOF_TIMESTAMPING_RX_HARDWARE in the selftest. How about 
others? e.g. the SOF_TIMESTAMPING_TX_* that will affect the sk->sk_error_queue 
which seems not good. If rx tstamp is useful, tx tstamp should be useful also?

>>
>> Enable BPF programs to actively request the generation of timestamps
>> from a stream socket. The also required ioctl(SIOCSHWTSTAMP) on the
>> network device must still be done separately, in user space.

hmm... so both ioctl(SIOCSHWTSTAMP) of the netdevice and the 
SOF_TIMESTAMPING_RX_HARDWARE of the sk must be done?

I likely miss something. When skb is created in the driver rx path, the sk is 
not known yet though. How the SOF_TIMESTAMPING_RX_HARDWARE of the sk affects the 
skb_shinfo(skb)->hwtstamps?