lguest: notify on empty

This is the lguest implementation of the VIRTIO_F_NOTIFY_ON_EMPTY feature.
It is currently only published for network devices, but it is turned on for
everyone.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 3be8ab2..82fafe0 100644 (file)
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -157,6 +157,9 @@ struct virtqueue
 
        /* The routine to call when the Guest pings us. */
        void (*handle_output)(int fd, struct virtqueue *me);
+
+       /* Outstanding buffers */
+       unsigned int inflight;
 };
 
 /* Remember the arguments to the program so we can "reboot" */
@@ -702,6 +705,7 @@ static unsigned get_vq_desc(struct virtqueue *vq,
                        errx(1, "Looped descriptor");
        } while ((i = next_desc(vq, i)) != vq->vring.num);
 
+       vq->inflight++;
        return head;
 }
 
@@ -719,6 +723,7 @@ static void add_used(struct virtqueue *vq, unsigned int head, int len)
        /* Make sure buffer is written before we update index. */
        wmb();
        vq->vring.used->idx++;
+       vq->inflight--;
 }
 
 /* This actually sends the interrupt for this virtqueue */
@@ -726,8 +731,9 @@ static void trigger_irq(int fd, struct virtqueue *vq)
 {
        unsigned long buf[] = { LHREQ_IRQ, vq->config.irq };
 
-       /* If they don't want an interrupt, don't send one. */
-       if (vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+       /* If they don't want an interrupt, don't send one, unless empty. */
+       if ((vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
+           && vq->inflight)
                return;
 
        /* Send the Guest an interrupt tell them we used something up. */
@@ -1107,6 +1113,7 @@ static void add_virtqueue(struct device *dev, unsigned int num_descs,
        vq->next = NULL;
        vq->last_avail_idx = 0;
        vq->dev = dev;
+       vq->inflight = 0;
 
        /* Initialize the configuration. */
        vq->config.num = num_descs;
@@ -1368,6 +1375,7 @@ static void setup_tun_net(const char *arg)
 
        /* Tell Guest what MAC address to use. */
        add_feature(dev, VIRTIO_NET_F_MAC);
+       add_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY);
        set_config(dev, sizeof(conf), &conf);
 
        /* We don't need the socket any more; setup is done. */