nvdimm: make get_memory_region() perform checks and initialization

We might get a call to get_memory_region() before the device has been
realized. We should return a consistent value, as the return value
will e.g. later on be used in the pre_plug handler.

To avoid duplicating too much code, factor the initialization and checks
out into a helper function.

Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180619134141.29478-12-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/mem/nvdimm.c

@@ -78,20 +78,22 @@ static void nvdimm_finalize(Object *obj)
     g_free(nvdimm->nvdimm_mr);
 }
 
-static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm, Error **errp)
+static void nvdimm_prepare_memory_region(NVDIMMDevice *nvdimm, Error **errp)
 {
-    NVDIMMDevice *nvdimm = NVDIMM(dimm);
+    PCDIMMDevice *dimm = PC_DIMM(nvdimm);
+    uint64_t align, pmem_size, size;
+    MemoryRegion *mr;
 
-    return nvdimm->nvdimm_mr;
-}
+    g_assert(!nvdimm->nvdimm_mr);
 
-static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp)
-{
-    MemoryRegion *mr = host_memory_backend_get_memory(dimm->hostmem);
-    NVDIMMDevice *nvdimm = NVDIMM(dimm);
-    uint64_t align, pmem_size, size = memory_region_size(mr);
+    if (!dimm->hostmem) {
+        error_setg(errp, "'" PC_DIMM_MEMDEV_PROP "' property must be set");
+        return;
+    }
 
+    mr = host_memory_backend_get_memory(dimm->hostmem);
     align = memory_region_get_alignment(mr);
+    size = memory_region_size(mr);
 
     pmem_size = size - nvdimm->label_size;
     nvdimm->label_data = memory_region_get_ram_ptr(mr) + pmem_size;
@@ -115,6 +117,30 @@ static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp)
     nvdimm->nvdimm_mr->align = align;
 }
 
+static MemoryRegion *nvdimm_get_memory_region(PCDIMMDevice *dimm, Error **errp)
+{
+    NVDIMMDevice *nvdimm = NVDIMM(dimm);
+    Error *local_err = NULL;
+
+    if (!nvdimm->nvdimm_mr) {
+        nvdimm_prepare_memory_region(nvdimm, &local_err);
+        if (local_err) {
+            error_propagate(errp, local_err);
+            return NULL;
+        }
+    }
+    return nvdimm->nvdimm_mr;
+}
+
+static void nvdimm_realize(PCDIMMDevice *dimm, Error **errp)
+{
+    NVDIMMDevice *nvdimm = NVDIMM(dimm);
+
+    if (!nvdimm->nvdimm_mr) {
+        nvdimm_prepare_memory_region(nvdimm, errp);
+    }
+}
+
 /*
  * the caller should check the input parameters before calling
  * label read/write functions.