virtio-input: fix eventq batching

virtio_input_send buffers input events until it sees a SYNC. Then it
either sends or drops the entire batch, depending on whether eventq
has enough space available. The case to avoid here is partial sends
where only part of the batch would get to the guest.

Using virtqueue_get_avail_bytes to check the state of eventq was not
correct. The queue may have a smaller number of larger buffers
available so bytes may be enough but the batch would still not be
possible to send, leading to the "Huh?  No vq elem available" error.

Instead of checking available bytes, this patch optimistically pops
buffers from the queue and puts them back in case it runs out of
space and the batch needs to be dropped.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Message-id: 1490365490-4854-3-git-send-email-lprosek@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/hw/input/virtio-input.c b/hw/input/virtio-input.c
index 728832aa627113800ee3c5bb1792df2e03dcae54..0e42f0d02c583e273fedf5dfa53568b41d2ff1b3 100644 (file)
--- a/hw/input/virtio-input.c
+++ b/hw/input/virtio-input.c
@@ -22,7 +22,6 @@
 void virtio_input_send(VirtIOInput *vinput, virtio_input_event *event)
 {
     VirtQueueElement *elem;
-    unsigned have, need;
     int i, len;
 
     if (!vinput->active) {
@@ -33,9 +32,9 @@ void virtio_input_send(VirtIOInput *vinput, virtio_input_event *event)
     if (vinput->qindex == vinput->qsize) {
         vinput->qsize++;
         vinput->queue = g_realloc(vinput->queue, vinput->qsize *
-                                  sizeof(virtio_input_event));
+                                  sizeof(vinput->queue[0]));
     }
-    vinput->queue[vinput->qindex++] = *event;
+    vinput->queue[vinput->qindex++].event = *event;
 
     /* ... until we see a report sync ... */
     if (event->type != cpu_to_le16(EV_SYN) ||
@@ -44,24 +43,24 @@ void virtio_input_send(VirtIOInput *vinput, virtio_input_event *event)
     }
 
     /* ... then check available space ... */
-    need = sizeof(virtio_input_event) * vinput->qindex;
-    virtqueue_get_avail_bytes(vinput->evt, &have, NULL, need, 0);
-    if (have < need) {
-        vinput->qindex = 0;
-        trace_virtio_input_queue_full();
-        return;
-    }
-
-    /* ... and finally pass them to the guest */
     for (i = 0; i < vinput->qindex; i++) {
         elem = virtqueue_pop(vinput->evt, sizeof(VirtQueueElement));
         if (!elem) {
-            /* should not happen, we've checked for space beforehand */
-            fprintf(stderr, "%s: Huh?  No vq elem available ...\n", __func__);
+            while (--i >= 0) {
+                virtqueue_unpop(vinput->evt, vinput->queue[i].elem, 0);
+            }
+            vinput->qindex = 0;
+            trace_virtio_input_queue_full();
             return;
         }
+        vinput->queue[i].elem = elem;
+    }
+
+    /* ... and finally pass them to the guest */
+    for (i = 0; i < vinput->qindex; i++) {
+        elem = vinput->queue[i].elem;
         len = iov_from_buf(elem->in_sg, elem->in_num,
-                           0, vinput->queue+i, sizeof(virtio_input_event));
+                           0, &vinput->queue[i].event, sizeof(virtio_input_event));
         virtqueue_push(vinput->evt, elem, len);
         g_free(elem);
     }

diff --git a/include/hw/virtio/virtio-input.h b/include/hw/virtio/virtio-input.h
index 55db31087ad558d32855299b6e6c919e23d6d7df..91df57eca4a78615c739c9996616c88b77d93088 100644 (file)
--- a/include/hw/virtio/virtio-input.h
+++ b/include/hw/virtio/virtio-input.h
@@ -62,7 +62,10 @@ struct VirtIOInput {
     VirtQueue                         *evt, *sts;
     char                              *serial;
 
-    virtio_input_event                *queue;
+    struct {
+        virtio_input_event event;
+        VirtQueueElement *elem;
+    }                                 *queue;
     uint32_t                          qindex, qsize;
 
     bool                              active;