Re: [PATCH bpf-next] bpf: Allow setting SO_TIMESTAMPING* with bpf_setsockopt()

[Martin KaFai Lau <martin.lau@linux.dev>]

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?