[PATCH net-next v4 0/6] net-timestamp: new tx tstamps and tcp

[Willem de Bruijn <willemb@google.com>]

Extend socket tx timestamping:
- allow multiple types of software timestamps aside from send (1)
- add software timestamp on enter packet scheduling (4)
- add software timestamp for TCP (5)
- add software timestamp for TCP on ACK (6)

The sk_flags option space is nearly exhausted. Also move the
many timestamp options to a new sk->sk_tstamps (2).

To disambiguate data when tstamps may arrive out of order,
optionally return a sequential ID assigned at send (3).

Extend Linux tx timestamping to monitoring of latency
incurred within the kernel stack and to protocols embedded in TCP.
Complex kernel setups may have multiple layers of queueing, including
multiple instances of packet scheduling, and many classes per layer.
Many applications embed discrete payloads into TCP bytestreams for
reliability, flow control, etcetera. Detecting application tail
latency in such scenarios relies on identifying the exact queue
responsible if on the host, or the network latency if otherwise.

Changelog:
v4->v5
  - define SCM_TSTAMP_SND == 0, for legacy behavior
  - add TCP tstamps without changing the generated byte stream
    - modify GSO and ACK to find offset: slightly more complex
      than previous invariant that it is the last byte
  - consistent naming of packet scheduling
    - rename SCM_TSTAMP_ENQ to SCM_TSTAMP_SCHED
  - add unique key in ee_data
  - add id field in ee_info to disambiguate tstamps
    - optional, only on new flag SOF_TIMESTAMPING_OPT_ID
    - for bytestream, in bytes

v3->v4
  - (v3 review comment) removed skb->mark packet identification (*A)
  - (v3 review comment) fixed indentation
  - tcp: fixed poll() to return POLLERR on non-zero queue
  - rebased to work without syststamp
  - comments: removed all traces of MSG_TSTAMP_.. (*B)

v2->v3
  - extend the SO_TIMESTAMPING API, instead of defining a new one.
  - add protocol independent support to correlate tstamps with data,
    based on returning skb->mark.
  - removed no-payload optimization and documentation (for now):

    I have a follow-on patch that reintroduces MSG_TSTAMP along with a
    new socket option SOF_TIMESTAMPING_OPT_ONFLAG. This is equivalent
    to sequence setsockopt(<enable>); send(..); setsockopt(<disable>),
    but avoids the need to define a MSG_TSTAMP_<TYPE> for each type.

    I will leave these three patches as follow-on, as this patchset is
    large enough as is.

v1->v2
  - expand timestamping (existing and new) to SOCK_RAW and ping sockets
  - rename sock_errqueue_timestamping to scm_timestamping
  - change timestamp data format: do not add fields to scm_timestamping.
      Doing so could break legacy applications. Instead, communicate
      through an existing, but unused, field in the error message.
  - rename SOF_.._OPT_TX_NO_PAYLOAD to shorter SOF_.._OPT_TSONLY
  - move msg_tstamp test app out of patchset and to github
      git://github.com/wdebruij/kerneltools.git


Willem de Bruijn (6):
  net-timestamp: extend SCM_TIMESTAMPING ancillary data struct
  net-timestamp: move timestamp flags out of sk_flags
  net-timestamp: add key to disambiguate concurrent datagrams
  net-timestamp: SCHED timestamp on entering packet scheduler
  net-timestamp: TCP timestamping
  net-timestamp: ACK timestamp for bytestreams

-- 
2.0.0.526.g5318336