lguest: don't force VIRTIO_F_NOTIFY_ON_EMPTY
VIRTIO_F_NOTIFY_ON_EMPTY indicates to the Guest that we will hit them with
an interrupt every time the xmit queue is emptied.
Because it results in lots of tx interrupts, modern Guests probably don't
want it, so let's only force it when they accept the option.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 84bbb19..ba9373f 100644
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -134,6 +134,9 @@
/* 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 @@
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 @@
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 @@
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);