Re: [PATCH net-next 0/9] net-timestamp: bpf extension to equip applications transparently

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Jason Xing wrote:
> From: Jason Xing <kernelxing@tencent.com>
> 
> A few weeks ago, I planned to extend SO_TIMESTMAMPING feature by using
> tracepoint to print information (say, tstamp) so that we can
> transparently equip applications with this feature and require no
> modification in user side.
> 
> Later, we discussed at netconf and agreed that we can use bpf for better
> extension, which is mainly suggested by John Fastabend and Willem de
> Bruijn. Many thanks here! So I post this series to see if we have a
> better solution to extend. 
> 
> This approach relies on existing SO_TIMESTAMPING feature, for tx path,
> users only needs to pass certain flags through bpf program to make sure
> the last skb from each sendmsg() has timestamp related controlled flag.
> For rx path, we have to use bpf_setsockopt() to set the sk->sk_tsflags
> and wait for the moment when recvmsg() is called.

As you mention, overall I am very supportive of having a way to add
timestamping by adminstrators, without having to rebuild applications.
BPF hooks seem to be the right place for this.

There is existing kprobe/kretprobe/kfunc support. Supporting
SO_TIMESTAMPING directly may be useful due to its targeted feature
set, and correlation between measurements for the same data in the
stream.
 
> After this series, we could step by step implement more advanced
> functions/flags already in SO_TIMESTAMPING feature for bpf extension.

My main implementation concern is where this API overlaps with the
existing user API, and how they might conflict. A few questions in the
patches.

Also, I'm not the best person to give in-depth BPF feedback.

> Here is the test output:
> 1) receive path
> iperf3-987305  [008] ...11 179955.200990: bpf_trace_printk: rx: port: 5201:55192, swtimestamp: 1728167973,670426346, hwtimestamp: 0,0
> 2) xmit path
> iperf3-19765   [013] ...11  2021.329602: bpf_trace_printk: tx: port: 47528:5201, key: 1036, timestamp: 1728357067,436678584
> iperf3-19765   [013] b..11  2021.329611: bpf_trace_printk: tx: port: 47528:5201, key: 1036, timestamp: 1728357067,436689976
> iperf3-19765   [013] ...11  2021.329622: bpf_trace_printk: tx: port: 47528:5201, key: 1036, timestamp: 1728357067,436700739