[PATCH 0 of 7 V4] Remus/Libxl: Network buffering support

[Shriram Rajagopalan <rshriram@cs.ubc.ca>]

This patch series adds support for network buffering in the Remus
codebase in libxl and makes the suspend callback asynchronous.

I have tested the series with PV guests (with and without suspend
event channel).  Would appreciate if anyone could test the series
with PV-HVM guests and pure HVM guests.

Changes in V4:

[1/7] *new*. This Ian Jackson's patch -- making 
      libxl__domain_suspend_callback asynchronous

[2/7] [was 1/5 in previous versions] Remove check for libnl
      command line utils

[3/7] [was 2/5 previously] minor nits

[4/7] [was 3/5 previously] define LIBXL_HAVE_REMUS_NETBUF
      in libxl.h

[5/7] [was 4/5 previously] clean ups. Make the usleep in checkpoint
      callback asynchronous

[6/7] [was 5/5 previously] minor nits

[7/7] *new*. Refactor libxl__domain_suspend_common_callback to
       substitute usleep based wait loops with libxl's timer events.

Changes in V3:
[1/5] Fix redundant checks in configure scripts
      (based on Ian Campbell's suggestions)

[2/5] Introduce locking in the script, during IFB setup.
      Add xenstore paths used by netbuf scripts
      to xenstore-paths.markdown

[3/5] Hotplug scripts setup/teardown invocations are now asynchronous
      following IanJ's feedback.  However, the invocations are still
      sequential. 

[5/5] Allow per-domain specification of netbuffer scripts in xl remus
      commmand.

And minor nits throughout the series based on feedback from
the last version

Changes in V2:
[1/5] Configure script will automatically enable/disable network
      buffer support depending on the availability of the appropriate
      libnl3 version. [If libnl3 is unavailable, a warning message will be
      printed to let the user know that the feature has been disabled.]

      use macros from pkg.m4 instead of pkg-config commands
      removed redundant checks for libnl3 libraries.

[3,4/5] - Minor nits.

Version 1:

[1/5] Changes to autoconf scripts to check for libnl3. Add linker flags
      to libxl Makefile.

[2/5] External script to setup/teardown network buffering using libnl3's
      CLI. This script will be invoked by libxl before starting Remus.
      The script's main job is to bring up an IFB device with plug qdisc
      attached to it.  It then re-routes egress traffic from the guest's
      vif to the IFB device.

[3/5] Libxl code to invoke the external setup script, followed by netlink
      related setup to obtain a handle on the output buffers attached
      to each vif.

[4/5] Libxl interaction with network buffer module in the kernel via
      libnl3 API.

[5/5] xl cmdline switch to explicitly enable network buffering when
      starting remus.


  Few things to note: 

    a) Based on previous email discussions, the setup/teardown task has
    been moved to a hotplug style shell script which can be customized as
    desired, instead of implementing it as C code inside libxl.

    b) Libnl3 is not available on NetBSD. Nor is it available on CentOS
   (Linux).  So I have made network buffering support an optional feature
   so that it can be disabled if desired.

   c) NetBSD does not have libnl3. So I have put the setup script under
   tools/hotplug/Linux folder.

thanks
shriram