[RFC PATCH 06/27] virtio: Add virtio_queue_get_used_notify_split

[Eugenio Pérez]

This function is just used for a few commits, so SW LM is developed
incrementally, and it is deleted after it is useful.

For a few commits, only the events (irqfd, eventfd) are forwarded.
This series adds descriptors forwarding on top of that.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 include/hw/virtio/virtio.h |  1 +
 hw/virtio/virtio.c         | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b7ece7a6a8..b9b8497ea0 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -225,6 +225,7 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int 
version_id);
 
 void virtio_notify_config(VirtIODevice *vdev);
 
+bool virtio_queue_get_used_notify_split(VirtQueue *vq);
 bool virtio_queue_get_notification(VirtQueue *vq);
 void virtio_queue_set_notification(VirtQueue *vq, int enable);
 
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index ceb58fda6c..3469946538 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -377,6 +377,20 @@ static inline void vring_used_idx_set(VirtQueue *vq, 
uint16_t val)
     vq->used_idx = val;
 }
 
+bool virtio_queue_get_used_notify_split(VirtQueue *vq)
+{
+    VRingMemoryRegionCaches *caches;
+    hwaddr pa = offsetof(VRingUsed, flags);
+    uint16_t flags;
+
+    RCU_READ_LOCK_GUARD();
+
+    caches = vring_get_region_caches(vq);
+    assert(caches);
+    flags = virtio_lduw_phys_cached(vq->vdev, &caches->used, pa);
+    return !(VRING_USED_F_NO_NOTIFY & flags);
+}
+
 /* Called within rcu_read_lock().  */
 static inline void vring_used_flags_set_bit(VirtQueue *vq, int mask)
 {
-- 
2.18.4