diff --git a/block.c b/block.c
index 19da114..002b442 100644
--- a/block.c
+++ b/block.c
@@ -730,6 +730,48 @@ int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags)
     return 0;
 }
 
+int bdrv_ensure_backing_file(BlockDriverState *bs)
+{
+    char backing_filename[PATH_MAX];
+    int back_flags, ret;
+    BlockDriver *back_drv = NULL;
+
+    if (bs->backing_hd != NULL) {
+        return 0;
+    }
+
+    bs->open_flags &= ~BDRV_O_NO_BACKING;
+    if (bs->backing_file[0] == '\0') {
+        return 0;
+    }
+
+    bs->backing_hd = bdrv_new("");
+    bdrv_get_full_backing_filename(bs, backing_filename,
+                                   sizeof(backing_filename));
+
+    if (bs->backing_format[0] != '\0') {
+        back_drv = bdrv_find_format(bs->backing_format);
+    }
+
+    /* backing files always opened read-only */
+    back_flags = bs->open_flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT);
+
+    ret = bdrv_open(bs->backing_hd, backing_filename, back_flags, back_drv);
+    if (ret < 0) {
+        bdrv_close(bs);
+        bdrv_delete(bs->backing_hd);
+        bs->backing_hd = NULL;
+        return ret;
+    }
+    if (bs->is_temporary) {
+        bs->backing_hd->keep_read_only = !(bs->open_flags & BDRV_O_RDWR);
+    } else {
+        /* base images use the same setting as leaf */
+        bs->backing_hd->keep_read_only = bs->keep_read_only;
+    }
+    return 0;
+}
+
 /*
  * Opens a disk image (raw, qcow2, vmdk, ...)
  */
@@ -813,34 +855,11 @@ int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
     }
 
     /* If there is a backing file, use it */
-    if ((flags & BDRV_O_NO_BACKING) == 0 && bs->backing_file[0] != '\0') {
-        char backing_filename[PATH_MAX];
-        int back_flags;
-        BlockDriver *back_drv = NULL;
-
-        bs->backing_hd = bdrv_new("");
-        bdrv_get_full_backing_filename(bs, backing_filename,
-                                       sizeof(backing_filename));
-
-        if (bs->backing_format[0] != '\0') {
-            back_drv = bdrv_find_format(bs->backing_format);
-        }
-
-        /* backing files always opened read-only */
-        back_flags =
-            flags & ~(BDRV_O_RDWR | BDRV_O_SNAPSHOT | BDRV_O_NO_BACKING);
-
-        ret = bdrv_open(bs->backing_hd, backing_filename, back_flags, back_drv);
+    if ((flags & BDRV_O_NO_BACKING) == 0) {
+        ret = bdrv_ensure_backing_file(bs);
         if (ret < 0) {
-            bdrv_close(bs);
             return ret;
         }
-        if (bs->is_temporary) {
-            bs->backing_hd->keep_read_only = !(flags & BDRV_O_RDWR);
-        } else {
-            /* base image inherits from "parent" */
-            bs->backing_hd->keep_read_only = bs->keep_read_only;
-        }
     }
 
     if (!bdrv_key_required(bs)) {
diff --git a/block.h b/block.h
index 9bff842..8aeb7a9 100644
--- a/block.h
+++ b/block.h
@@ -122,6 +122,7 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top);
 void bdrv_delete(BlockDriverState *bs);
 int bdrv_parse_cache_flags(const char *mode, int *flags);
 int bdrv_file_open(BlockDriverState **pbs, const char *filename, int flags);
+int bdrv_ensure_backing_file(BlockDriverState *bs);
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv);
 void bdrv_close(BlockDriverState *bs);