From 7808121b9a1e44ef12fecd49fa6c268f27a150fc Mon Sep 17 00:00:00 2001
From: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Date: Wed, 8 Sep 2010 18:10:42 -0400
Subject: [PATCH] xenbus: avoid zero returns from read()

It is possible to get a zero return from read() in instances where the
queue is not empty but has no elements with data to deliver to the user.
Since a zero return from read is an error indicator, resume waiting or
return -EAGAIN (for a nonblocking fd) in this case.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
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