[PATCH] virtio_blk.c: Add documentation for vring_enable_cb()

[Jes.Sorensen@redhat.com]

From: Jes Sorensen <Jes.Sorensen@redhat.com>

Add documentation for vring_enable_cb() as return logic may not be
obvious for the caller.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
---
 drivers/virtio/virtio_ring.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 0f90634..2cdcdca 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -333,6 +333,11 @@ static void vring_disable_cb(struct virtqueue *_vq)
 	vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 }
 
+/*
+ * Enable interrupts and check whether there is anything in the queue.
+ * Note, vring_enable_cb() returns TRUE if the queue is empty,  and
+ * FALSE if the queue is not empty and there is work to do.
+ */
 static bool vring_enable_cb(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
-- 
1.6.5.2