implement O_NONBLOCK for /proc/xen/xenbus

This patch implements O_NONBLOCK for /proc/xen/xenbus.  It is a simple
matter of returning -EAGAIN instead of waiting on a queue.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c
index a9592d981b1..9d5b519d2e4 100644
--- a/drivers/xen/xenfs/xenbus.c
+++ b/drivers/xen/xenfs/xenbus.c
@@ -122,6 +122,9 @@ static ssize_t xenbus_file_read(struct file *filp,
         mutex_lock(&u->reply_mutex);
         while (list_empty(&u->read_buffers)) {
                 mutex_unlock(&u->reply_mutex);
+                if (filp->f_flags & O_NONBLOCK)
+                        return -EAGAIN;
+
                 ret = wait_event_interruptible(u->read_waitq,
                                                !list_empty(&u->read_buffers));
                 if (ret)