Merge branch 'net-timestamp-bpf-extension-to-equip-applications-transparently'

Merge branch 'net-timestamp-bpf-extension-to-equip-applications-transparently'

Jason Xing says:

====================
net-timestamp: bpf extension to equip applications transparently

"Timestamping is key to debugging network stack latency. With
SO_TIMESTAMPING, bugs that are otherwise incorrectly assumed to be
network issues can be attributed to the kernel." This is extracted
from the talk "SO_TIMESTAMPING: Powering Fleetwide RPC Monitoring"
addressed by Willem de Bruijn at netdevconf 0x17).

There are a few areas that need optimization with the consideration of
easier use and less performance impact, which I highlighted and mainly
discussed at netconf 2024 with Willem de Bruijn and John Fastabend:
uAPI compatibility, extra system call overhead, and the need for
application modification. I initially managed to solve these issues
by writing a kernel module that hooks various key functions. However,
this approach is not suitable for the next kernel release. Therefore,
a BPF extension was proposed. During recent period, Martin KaFai Lau
provides invaluable suggestions about BPF along the way. Many thanks
here!

This series adds the BPF networking timestamping infrastructure through
reusing most of the tx timestamping callback that is currently enabled
by the SO_TIMESTAMPING.. This series also adds TX timestamping support
for TCP. The RX timestamping and UDP support will be added in the future.
====================

Link: https://patch.msgid.link/20250220072940.99994-1-kerneljasonxing@gmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>