1 files changed, 21 insertions, 4 deletions

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 84bbb190bf7b..ba9373f82ab5 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -134,6 +134,9 @@ struct device {
         /* Is it operational */
         bool running;
 
+        /* Does Guest want an intrrupt on empty? */
+        bool irq_on_empty;
+
         /* Device-specific data. */
         void *priv;
 };
@@ -624,10 +627,13 @@ static void trigger_irq(struct virtqueue *vq)
                 return;
         vq->pending_used = 0;
 
-        /* If they don't want an interrupt, don't send one, unless empty. */
-        if ((vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
-            && lg_last_avail(vq) != vq->vring.avail->idx)
-                return;
+        /* If they don't want an interrupt, don't send one... */
+        if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT) {
+                /* ... unless they've asked us to force one on empty. */
+                if (!vq->dev->irq_on_empty
+                    || lg_last_avail(vq) != vq->vring.avail->idx)
+                        return;
+        }
 
         /* Send the Guest an interrupt tell them we used something up. */
         if (write(lguest_fd, buf, sizeof(buf)) != 0)
@@ -1043,6 +1049,15 @@ static void create_thread(struct virtqueue *vq)
         close(vq->eventfd);
 }
 
+static bool accepted_feature(struct device *dev, unsigned int bit)
+{
+        const u8 *features = get_feature_bits(dev) + dev->feature_len;
+
+        if (dev->feature_len < bit / CHAR_BIT)
+                return false;
+        return features[bit / CHAR_BIT] & (1 << (bit % CHAR_BIT));
+}
+
 static void start_device(struct device *dev)
 {
         unsigned int i;
@@ -1056,6 +1071,8 @@ static void start_device(struct device *dev)
                 verbose(" %02x", get_feature_bits(dev)
                         [dev->feature_len+i]);
 
+        dev->irq_on_empty = accepted_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
+
         for (vq = dev->vq; vq; vq = vq->next) {
                 if (vq->service)
                         create_thread(vq);