Re: [PATCH net-next v2 09/12] net-timestamp: add tx OPT_ID_TCP support for bpf case

Jason Xing wrote:

From: Jason Xing <kernelxing@tencent.com>

We can set OPT_ID|OPT_ID_TCP before we initialize the last skb
from each sendmsg. We only set the socket once like how we use
setsockopt() with OPT_ID|OPT_ID_TCP flags.

Note: we will check if non-bpf _and_ bpf sk_tsflags have OPT_ID
flag. If either of them has been set before, we will not initialize
the key any more, 

Where and how is this achieved?

Also be aware of the subtle distinction between passing OPT_ID_TCP
along with OPT_ID or not.