[PATCHv3 0/11] Xen: FIFO-based event channel ABI

[David Vrabel <david.vrabel@citrix.com>]

This is a complete implementation of the hypervisor parts of the
FIFO-based event channel ABI described in this design document:

http://xenbits.xen.org/people/dvrabel/event-channels-E.pdf

Changes in draft E are:

- Control blocks are no longer required to be in the same page as the
  vcpu_info.
- Added padding to struct evtchn_init_control.

Remaining work:

* Extend libxl and xl to allow the event channel limit to be set.
  Without this DomUs are limited the default number of event channels
  (4096).  I use a trivial C program to set the limit.

* Decide whether EVTCHNOP_set_limit should be a DOMCTL instead.

* Allocation of struct event channels to use less memory when fewer
  event channels are in use. I plan to have d->evtchns point to a page
  contains N struct evtchns and M group pointers with the remainder
  event channels being indexed by group/bucket in patch 6.

Patch 1-4 do some preparatory work for supporting alternate ABIs.

Patch 5-6 expand the number of evtchn objects a domain may have to
changing how they are allocated.

Patch 7 adds the ABI.

Patch 8 adds the EVTCHNOP_set_priority implementation.  This will
return -ENOSYS for ABIs that do not support priority.

Patch 9-10 adds the EVTCHNOP_set_limit implementation and adds a
function to libxc. This will also work with the 2-level ABI.

Patch 11 adds the FIFO-based ABI implementation.

Changes in v3:

- Updates for Draft E of the design.
- Store priority in struct evtchn.
- Implement set_priority with generic code + hook.
- Implement set_limit and add libxc function.
- Add ABI specific output to 'e' debug key.

Changes in v2:

- Updates for Draft D of the design.
- 130,000+ event channels are now supported.
- event_port.c -> event_2l.c and only contains 2l functions.
- Addresses various review comments
  - int -> unsigned in lots of places
  - use write_atomic() to set HEAD
  - removed MAX_EVTCHNS
  - evtchn_ops are const.
- Pack struct evtchns better to reduce memory needed.