[Qemu-devel] [PATCH v3 1/3] balloon: Don't try fetching info if guest is unresponsive

[Amit Shah <amit.shah@redhat.com>]

If the guest is unresponsive and 'info balloon' is invoked, the monitor
process just hangs waiting for info from the guest. Return the most
recent balloon data in that case.

A new timer is added, which on expiry, just presents the old data to the
monitor callback functions.

See https://bugzilla.redhat.com/show_bug.cgi?id=623903

Reported-by: <lihuang@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
---
 hw/virtio-balloon.c |   11 +++++++++++
 1 files changed, 11 insertions(+), 0 deletions(-)

diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index 9fe3886..d6c66cf 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -40,6 +40,7 @@ typedef struct VirtIOBalloon
     size_t stats_vq_offset;
     MonitorCompletion *stats_callback;
     void *stats_opaque_callback_data;
+    QEMUTimer *timer;
 } VirtIOBalloon;
 
 static VirtIOBalloon *to_virtio_balloon(VirtIODevice *vdev)
@@ -137,6 +138,11 @@ static void complete_stats_request(VirtIOBalloon *vb)
     vb->stats_callback = NULL;
 }
 
+static void show_old_stats(void *opaque)
+{
+    complete_stats_request(opaque);
+}
+
 static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
 {
     VirtIOBalloon *s = DO_UPCAST(VirtIOBalloon, vdev, vdev);
@@ -148,6 +154,8 @@ static void virtio_balloon_receive_stats(VirtIODevice *vdev, VirtQueue *vq)
         return;
     }
 
+    qemu_del_timer(s->timer);
+
     /* Initialize the stats to get rid of any stale values.  This is only
      * needed to handle the case where a guest supports fewer stats than it
      * used to (ie. it has booted into an old kernel).
@@ -215,6 +223,7 @@ static void virtio_balloon_to_target(void *opaque, ram_addr_t target,
         dev->stats_callback = cb;
         dev->stats_opaque_callback_data = cb_data; 
         if (dev->vdev.guest_features & (1 << VIRTIO_BALLOON_F_STATS_VQ)) {
+            qemu_mod_timer(dev->timer, qemu_get_clock(rt_clock) + 5000);
             virtqueue_push(dev->svq, &dev->stats_vq_elem, dev->stats_vq_offset);
             virtio_notify(&dev->vdev, dev->svq);
         } else {
@@ -267,6 +276,8 @@ VirtIODevice *virtio_balloon_init(DeviceState *dev)
     s->dvq = virtio_add_queue(&s->vdev, 128, virtio_balloon_handle_output);
     s->svq = virtio_add_queue(&s->vdev, 128, virtio_balloon_receive_stats);
 
+    s->timer = qemu_new_timer(rt_clock, show_old_stats, s);
+
     reset_stats(s);
     qemu_add_balloon_handler(virtio_balloon_to_target, s);
 
-- 
1.7.2.2