[RFC PATCH net-next v6 00/13] net-timestamp: bpf extension to equip applications transparently

[Jason Xing <kerneljasonxing@gmail.com>]

"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!

In this series, I only support foundamental codes and tx for TCP.
This approach mostly relies on existing SO_TIMESTAMPING feature, users
only needs to pass certain flags through bpf_setsocktopt() to a separate
tsflags. Please see the last selftest patch in this series.

After this series, we could step by step implement more advanced
functions/flags already in SO_TIMESTAMPING feature for bpf extension.

---
RFC v6
In the meantime, any suggestions and reviews are welcome!
Link: https://lore.kernel.org/all/20250112113748.73504-1-kerneljasonxing@gmail.com/
1. handle those safety problem by using the correct method.
2. support bpf_getsockopt.
3. adjust the position of BPF_SOCK_OPS_TS_TCP_SND_CB
4. fix mishandling the hardware timestamp error
5. add more corresponding tests

v5
Link: https://lore.kernel.org/all/20241207173803.90744-1-kerneljasonxing@gmail.com/
1. handle the safety issus when someone tries to call unrelated bpf
helpers.
2. avoid adding direct function call in the hot path like
__dev_queue_xmit()
3. remove reporting the hardware timestamp and tskey since they can be
fetched through the existing helper with the help of
bpf_skops_init_skb(), please see the selftest.
4. add new sendmsg callback in tcp_sendmsg, and introduce tskey_bpf used
by bpf program to correlate tcp_sendmsg with other hook points in patch [13/15].

v4
Link: https://lore.kernel.org/all/20241028110535.82999-1-kerneljasonxing@gmail.com/
1. introduce sk->sk_bpf_cb_flags to let user use bpf_setsockopt() (Martin)
2. introduce SKBTX_BPF to enable the bpf SO_TIMESTAMPING feature (Martin)
3. introduce bpf map in tests (Martin)
4. I choose to make this series as simple as possible, so I only support
most cases in the tx path for TCP protocol.

v3
Link: https://lore.kernel.org/all/20241012040651.95616-1-kerneljasonxing@gmail.com/
1. support UDP proto by introducing a new generation point.
2. for OPT_ID, introducing sk_tskey_bpf_offset to compute the delta
between the current socket key and bpf socket key. It is desiged for
UDP, which also applies to TCP.
3. support bpf_getsockopt()
4. use cgroup static key instead.
5. add one simple bpf selftest to show how it can be used.
6. remove the rx support from v2 because the number of patches could
exceed the limit of one series.

V2
Link: https://lore.kernel.org/all/20241008095109.99918-1-kerneljasonxing@gmail.com/
1. Introduce tsflag requestors so that we are able to extend more in the
future. Besides, it enables TX flags for bpf extension feature separately
without breaking users. It is suggested by Vadim Fedorenko.
2. introduce a static key to control the whole feature. (Willem)
3. Open the gate of bpf_setsockopt for the SO_TIMESTAMPING feature in
some TX/RX cases, not all the cases.


Jason Xing (13):
  net-timestamp: add support for bpf_setsockopt()
  net-timestamp: prepare for timestamping callbacks use
  bpf: stop UDP sock accessing TCP fields in bpf callbacks
  bpf: stop UDP sock accessing TCP fields in sock_op BPF CALLs
  net-timestamp: prepare for isolating two modes of SO_TIMESTAMPING
  net-timestamp: support SCM_TSTAMP_SCHED for bpf extension
  net-timestamp: support sw SCM_TSTAMP_SND for bpf extension
  net-timestamp: support hw SCM_TSTAMP_SND for bpf extension
  net-timestamp: support SCM_TSTAMP_ACK for bpf extension
  net-timestamp: make TCP tx timestamp bpf extension work
  net-timestamp: add a new callback in tcp_tx_timestamp()
  net-timestamp: introduce cgroup lock to avoid affecting non-bpf cases
  bpf: add simple bpf tests in the tx path for so_timestamping feature

 include/linux/filter.h                        |   1 +
 include/linux/skbuff.h                        |  25 +-
 include/net/sock.h                            |  10 +
 include/net/tcp.h                             |   4 +-
 include/uapi/linux/bpf.h                      |  31 +++
 net/core/dev.c                                |   5 +-
 net/core/filter.c                             |  50 +++-
 net/core/skbuff.c                             |  67 +++++-
 net/core/sock.c                               |  13 +
 net/dsa/user.c                                |   2 +-
 net/ipv4/tcp.c                                |  11 +
 net/ipv4/tcp_input.c                          |   9 +-
 net/ipv4/tcp_output.c                         |   8 +
 net/socket.c                                  |   2 +-
 tools/include/uapi/linux/bpf.h                |  24 ++
 .../bpf/prog_tests/so_timestamping.c          |  98 ++++++++
 .../selftests/bpf/progs/so_timestamping.c     | 227 ++++++++++++++++++
 17 files changed, 563 insertions(+), 24 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/so_timestamping.c
 create mode 100644 tools/testing/selftests/bpf/progs/so_timestamping.c

-- 
2.43.5