memory: add getter for owner

Whenever memory regions are accessed outside the BQL, they need to be
preserved against hot-unplug.  MemoryRegions actually do not have their
own reference count; they piggyback on a QOM object, their "owner".
The owner is set at creation time, and there is a function to retrieve
the owner.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

include/exec/memory.h

@@ -381,6 +381,13 @@ void memory_region_init_iommu(MemoryRegion *mr,
  */
 void memory_region_destroy(MemoryRegion *mr);
 
+/**
+ * memory_region_owner: get a memory region's owner.
+ *
+ * @mr: the memory region being queried.
+ */
+struct Object *memory_region_owner(MemoryRegion *mr);
+
 /**
  * memory_region_size: get a memory region's size.
  *

memory.c

@@ -738,6 +738,7 @@ void memory_region_init(MemoryRegion *mr,
     mr->owner = owner;
     mr->iommu_ops = NULL;
     mr->parent = NULL;
+    mr->owner = NULL;
     mr->size = int128_make64(size);
     if (size == UINT64_MAX) {
         mr->size = int128_2_64();
@@ -1013,6 +1014,11 @@ void memory_region_destroy(MemoryRegion *mr)
     g_free(mr->ioeventfds);
 }
 
+Object *memory_region_owner(MemoryRegion *mr)
+{
+    return mr->owner;
+}
+
 uint64_t memory_region_size(MemoryRegion *mr)
 {
     if (int128_eq(mr->size, int128_2_64())) {