Since QEMU is already able to emulate ioeventfd using pipefd, we're already
pretty close to supporting vhost-user on non-Linux systems.

This two patches bridge the gap by:

1. Adding a new event_notifier_get_wfd() to return wfd on the places where
   the peer is expected to write to the notifier.

2. Modifying the build system to it allows enabling vhost-user on BSD.

v1->v2:
  - Drop: "Allow returning EventNotifier's wfd" (Alex Williamson)
  - Add: "event_notifier: add event_notifier_get_wfd()" (Alex Williamson)
  - Add: "vhost: use wfd on functions setting vring call fd"
  - Rename: "Allow building vhost-user in BSD" to "configure, meson: allow
    enabling vhost-user on all POSIX systems"
  - Instead of making possible enabling vhost-user on Linux and BSD systems,
    allow enabling it on all non-Windows platforms. (Paolo Bonzini)

v2->v3:
  - Add a section to docs/interop/vhost-user.rst explaining how vhost-user
    is supported on non-Linux platforms. (Stefan Hajnoczi)

v3->v4:
  - Some documentation fixes. (Stefan Hajnoczi)
  - Pick up Reviewed-by tags.

Sergio Lopez (4):
  event_notifier: add event_notifier_get_wfd()
  vhost: use wfd on functions setting vring call fd
  configure, meson: allow enabling vhost-user on all POSIX systems
  docs: vhost-user: add subsection for non-Linux platforms

 configure                     |  4 ++--
 docs/interop/vhost-user.rst   | 20 ++++++++++++++++++++
 hw/virtio/vhost.c             |  6 +++---
 include/qemu/event_notifier.h |  1 +
 meson.build                   |  2 +-
 util/event_notifier-posix.c   |  5 +++++
 6 files changed, 32 insertions(+), 6 deletions(-)

-- 
2.35.1