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>
---
drivers/xen/xenfs/xenbus.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c
index c4c7db8363e76..55791dd1105f3 100644
--- a/drivers/xen/xenfs/xenbus.c
+++ b/drivers/xen/xenfs/xenbus.c
@@ -120,6 +120,7 @@ static ssize_t xenbus_file_read(struct file *filp,
int ret;
mutex_lock(&u->reply_mutex);
+again:
while (list_empty(&u->read_buffers)) {
mutex_unlock(&u->reply_mutex);
if (filp->f_flags & O_NONBLOCK)
@@ -158,6 +159,8 @@ static ssize_t xenbus_file_read(struct file *filp,
struct read_buffer, list);
}
}
+ if (i == 0)
+ goto again;
out:
mutex_unlock(&u->reply_mutex);
--
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