[RFC PATCH v8 19/21] vhost: Add reference counting to vhost_iova_tree

[Eugenio Pérez]

Now that different vqs can have different ASIDs its easier to track them
using reference counters.

QEMU's glib version still does not have them so we've copied g_rc_box,
so the implementation can be converted to glib's one when the minimum
version is raised.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
---
 hw/virtio/vhost-iova-tree.h |  5 +++--
 hw/virtio/vhost-iova-tree.c | 21 +++++++++++++++++++--
 2 files changed, 22 insertions(+), 4 deletions(-)

diff --git a/hw/virtio/vhost-iova-tree.h b/hw/virtio/vhost-iova-tree.h
index 1ffcdc5b57..bacd17d99c 100644
--- a/hw/virtio/vhost-iova-tree.h
+++ b/hw/virtio/vhost-iova-tree.h
@@ -16,8 +16,9 @@
 typedef struct VhostIOVATree VhostIOVATree;
 
 VhostIOVATree *vhost_iova_tree_new(uint64_t iova_first, uint64_t iova_last);
-void vhost_iova_tree_delete(VhostIOVATree *iova_tree);
-G_DEFINE_AUTOPTR_CLEANUP_FUNC(VhostIOVATree, vhost_iova_tree_delete);
+VhostIOVATree *vhost_iova_tree_acquire(VhostIOVATree *iova_tree);
+void vhost_iova_tree_release(VhostIOVATree *iova_tree);
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(VhostIOVATree, vhost_iova_tree_release);
 
 const DMAMap *vhost_iova_tree_find(const VhostIOVATree *iova_tree,
                                    const DMAMap *map);
diff --git a/hw/virtio/vhost-iova-tree.c b/hw/virtio/vhost-iova-tree.c
index 1a59894385..208476b3db 100644
--- a/hw/virtio/vhost-iova-tree.c
+++ b/hw/virtio/vhost-iova-tree.c
@@ -28,6 +28,9 @@ struct VhostIOVATree {
 
     /* IOVA address to qemu memory maps. */
     IOVATree *iova_taddr_map;
+
+    /* Reference count */
+    size_t refcnt;
 };
 
 /**
@@ -44,14 +47,28 @@ VhostIOVATree *vhost_iova_tree_new(hwaddr iova_first, 
hwaddr iova_last)
     tree->iova_last = iova_last;
 
     tree->iova_taddr_map = iova_tree_new();
+    tree->refcnt = 1;
     return tree;
 }
 
 /**
- * Delete an iova tree
+ * Increases the reference count of the iova tree
+ */
+VhostIOVATree *vhost_iova_tree_acquire(VhostIOVATree *iova_tree)
+{
+    ++iova_tree->refcnt;
+    return iova_tree;
+}
+
+/**
+ * Decrease reference counter of iova tree, freeing if it reaches 0
  */
-void vhost_iova_tree_delete(VhostIOVATree *iova_tree)
+void vhost_iova_tree_release(VhostIOVATree *iova_tree)
 {
+    if (--iova_tree->refcnt) {
+        return;
+    }
+
     iova_tree_destroy(iova_tree->iova_taddr_map);
     g_free(iova_tree);
 }
-- 
2.27.0