[PATCH 1/2] virtio: add a way to disable a queue

[Laurent Vivier]

Add virtio_queue_disable()/virtio_queue_enable() to disable/enable a queue
by setting vring.num to 0 (or num_default).
This is needed to be able to disable a guest driver from the host side

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
---
 include/hw/virtio/virtio.h |  2 ++
 hw/virtio/virtio.c         | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 8bab9cfb7507..6a3f71b4cd88 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -251,6 +251,8 @@ void virtio_config_modern_writel(VirtIODevice *vdev,
                                  uint32_t addr, uint32_t data);
 void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr);
 hwaddr virtio_queue_get_addr(VirtIODevice *vdev, int n);
+void virtio_queue_enable(VirtIODevice *vdev, int n);
+void virtio_queue_disable(VirtIODevice *vdev, int n);
 void virtio_queue_set_num(VirtIODevice *vdev, int n, int num);
 int virtio_queue_get_num(VirtIODevice *vdev, int n);
 int virtio_queue_get_max_num(VirtIODevice *vdev, int n);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 874377f37a70..fa5228c1a2d6 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2244,6 +2244,16 @@ void virtio_queue_set_rings(VirtIODevice *vdev, int n, 
hwaddr desc,
     virtio_init_region_cache(vdev, n);
 }
 
+void virtio_queue_disable(VirtIODevice *vdev, int n)
+{
+    vdev->vq[n].vring.num = 0;
+}
+
+void virtio_queue_enable(VirtIODevice *vdev, int n)
+{
+    vdev->vq[n].vring.num = vdev->vq[n].vring.num_default;
+}
+
 void virtio_queue_set_num(VirtIODevice *vdev, int n, int num)
 {
     /* Don't allow guest to flip queue between existent and
-- 
2.31.1