Xen devel - Apr 2007 - [PATCH] Add fallback code to blktap for missing poll-on-aio support

Hey,
	As Stephen explains in this mail:

  http://lists.xensource.com/archives/html/xen-devel/2006-10/msg00331.html

	blktap requires a xen specific kernel AIO ABI which has been vetoed by
upstream in favour of another approach. Rather than include this ABI,
Fedora has been carrying a patch which makes tap:aio use a thread to
poll for aio events and notify the main thread via a pipe.

	The upstream approach of allowing io_getevents() poll normal file
descriptors via epoll is still progressing:

  http://lkml.org/lkml/2007/1/3/16

	but when that does make it upstream, blktap will require significant
re-working to use that approach.

	In the meantime, here''s a patch which uses the poll-in-a-thread
approach only if AIO poll support isn''t available. It also hides the
details behind a simple abstraction and makes both tap:aio and tap:qcow
use it.

	Built and tested on 3.0.5 ... unless I''m jinxed :-)

  Signed-off-by: Mark McLoughlin <markmc@redhat.com>

Cheers,
Mark.


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