netdev - Re: [PATCH bpf-next v12 10/12] bpf: add BPF_SOCK_OPS_TS_SND

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Message-ID: <67b49823437e5_10d6a329419@willemb.c.googlers.com.notmuch>
Date: Tue, 18 Feb 2025 09:24:35 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 davem@...emloft.net, 
 edumazet@...gle.com, 
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Cc: bpf@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kerneljasonxing@...il.com>
Subject: Re: [PATCH bpf-next v12 10/12] bpf: add BPF_SOCK_OPS_TS_SND_CB
 callback

Jason Xing wrote:
> This patch introduces a new callback in tcp_tx_timestamp() to correlate
> tcp_sendmsg timestamp with timestamps from other tx timestamping
> callbacks (e.g., SND/SW/ACK).
> 
> Without this patch, BPF program wouldn't know which timestamps belong
> to which flow because of no socket lock protection. This new callback
> is inserted in tcp_tx_timestamp() to address this issue because
> tcp_tx_timestamp() still owns the same socket lock with
> tcp_sendmsg_locked() in the meanwhile tcp_tx_timestamp() initializes
> the timestamping related fields for the skb, especially tskey. The
> tskey is the bridge to do the correlation.
> 
> For TCP, BPF program hooks the beginning of tcp_sendmsg_locked() and
> then stores the sendmsg timestamp at the bpf_sk_storage, correlating
> this timestamp with its tskey that are later used in other sending
> timestamping callbacks.
> 
> Signed-off-by: Jason Xing <kerneljasonxing@...il.com>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>