From: Willem de Bruijn <willemb@google.com>
Date: Wed, 30 Jul 2014 11:48:43 -0400

Extend socket tx timestamping:
- allow multiple types of software timestamps aside from send (1)
- add software timestamp on tc enqueue (3)
- add software timestamp for TCP (4)
- add software timestamp for TCP on ACK (5)

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

The patchset extends 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 traffic shaping, 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.

I'm mostly fine with this patchset, the only major blocker is the bit
that changes TCP segmenting behavior when timestamps are enabled.  I
really don't want to see us doing that, because that makes the
timestamps non-passive.

Please work towards a solution to that problem and also fixup the
minor naming et al. issues I brought up too.

Thanks.