[PATCH bpf-next 0/2] TCP-BPF event notification support

[Sowmini Varadhan <sowmini.varadhan@oracle.com>]

This patchset uses eBPF perf-event based notification mechanism to solve
the problem described in 
   https://marc.info/?l=linux-netdev&m=154022219423571&w=2.
Thanks to Daniel Borkmann for feedback/input.

The problem statement is
  We would like to monitor some subset of TCP sockets in user-space,
  (the monitoring application would define 4-tuples it wants to monitor)
  using TCP_INFO stats to analyze reported problems. The idea is to
  use those stats to see where the bottlenecks are likely to be ("is it
  application-limited?" or "is there evidence of BufferBloat in the
  path?" etc)

  Today we can do this by periodically polling for tcp_info, but this
  could be made more efficient if the kernel would asynchronously
  notify the application via tcp_info when some "interesting"
  thresholds (e.g., "RTT variance > X", or "total_retrans > Y" etc)
  are reached. And to make this effective, it is better if
  we could apply the threshold check *before* constructing the
  tcp_info netlink notification, so that we don't waste resources
  constructing notifications that will be discarded by the filter.

This patchset solves the problem by adding perf-event based notification
support for sock_ops (Patch1). The eBPF kernel module can thus 
be designed to apply any desired filters to the bpf_sock_ops and
trigger a perf-event notification based on the verdict from the filter.
The uspace component can use these perf-event notifications to either
read any state managed by the eBPF kernel module, or issue a TCP_INFO 
netlink call if desired.

Patch 2 provides a simple example that shows how to use this infra
(and also provides a test case for it)

Sowmini Varadhan (2):
  bpf: add perf-event notificaton support for sock_ops
  selftests/bpf: add a test case for sock_ops perf-event notification

 net/core/filter.c                                 |   19 ++
 tools/testing/selftests/bpf/Makefile              |    4 +-
 tools/testing/selftests/bpf/perf-sys.h            |   74 ++++++++
 tools/testing/selftests/bpf/test_tcpnotify.h      |   19 ++
 tools/testing/selftests/bpf/test_tcpnotify_kern.c |   95 +++++++++++
 tools/testing/selftests/bpf/test_tcpnotify_user.c |  186 +++++++++++++++++++++
 6 files changed, 396 insertions(+), 1 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/perf-sys.h
 create mode 100644 tools/testing/selftests/bpf/test_tcpnotify.h
 create mode 100644 tools/testing/selftests/bpf/test_tcpnotify_kern.c
 create mode 100644 tools/testing/selftests/bpf/test_tcpnotify_user.c