[10/12] block: learn to open a driver with a given opaque

diff --git a/block.c b/block.c
index b421083..bdffb42 100644
--- a/block.c
+++ b/block.c
@@ -295,7 +295,7 @@  void bdrv_register(BlockDriver *bdrv)
 
 /* create a new block device (by default it is empty) */
 static BlockDriverState *bdrv_new_int(const char *device_name,
-    BlockDriverState *child)
+    BlockDriverState *child, void *opaque)
 {
     BlockDriverState *bs;
 
@@ -307,13 +307,14 @@  static BlockDriverState *bdrv_new_int(const char *device_name,
     bdrv_iostatus_disable(bs);
     notifier_list_init(&bs->close_notifiers);
     bs->child = child;
+    bs->opaque = opaque;
 
     return bs;
 }
 
 BlockDriverState *bdrv_new(const char *device_name)
 {
-    return bdrv_new_int(device_name, NULL);
+    return bdrv_new_int(device_name, NULL, NULL);
 }
 
 void bdrv_add_close_notifier(BlockDriverState *bs, Notifier *notify)
@@ -729,7 +730,9 @@  static int bdrv_open_common(BlockDriverState *bs, BlockDriverState *file,
     }
 
     bs->drv = drv;
-    bs->opaque = g_malloc0(drv->instance_size);
+    if (bs->opaque == NULL) {
+        bs->opaque = g_malloc0(drv->instance_size);
+    }
 
     bs->enable_write_cache = !!(flags & BDRV_O_CACHE_WB);
 
@@ -777,7 +780,7 @@  free_and_fail:
 }
 
 static int bdrv_file_open_int(BlockDriverState **pbs, const char *filename,
-    QDict *options, int flags, BlockDriverState *child)
+    QDict *options, int flags, BlockDriverState *child, void *opaque)
 {
     BlockDriverState *bs;
     BlockDriver *drv;
@@ -789,7 +792,7 @@  static int bdrv_file_open_int(BlockDriverState **pbs, const char *filename,
         options = qdict_new();
     }
 
-    bs = bdrv_new_int("", child);
+    bs = bdrv_new_int("", child, opaque);
     bs->options = options;
     options = qdict_clone_shallow(options);
 
@@ -882,18 +885,11 @@  fail:
 int bdrv_file_open(BlockDriverState **pbs, const char *filename,
                    QDict *options, int flags)
 {
-    return bdrv_file_open_int(pbs, filename, options, flags, NULL);
+    return bdrv_file_open_int(pbs, filename, options, flags, NULL, NULL);
 }
 
-/*
- * Opens the backing file for a BlockDriverState if not yet open
- *
- * options is a QDict of options to pass to the block drivers, or NULL for an
- * empty set of options. The reference to the QDict is transferred to this
- * function (even on failure), so if the caller intends to reuse the dictionary,
- * it needs to use QINCREF() before calling bdrv_file_open.
- */
-int bdrv_open_backing_file(BlockDriverState *bs, QDict *options)
+static int bdrv_open_backing_file_int(BlockDriverState *bs,
+    QDict *options, void *opaque)
 {
     char backing_filename[PATH_MAX];
     int back_flags, ret;
@@ -917,7 +913,7 @@  int bdrv_open_backing_file(BlockDriverState *bs, QDict *options)
         return 0;
     }
 
-    bs->backing_hd = bdrv_new_int("", bs);
+    bs->backing_hd = bdrv_new_int("", bs, opaque);
     bdrv_get_full_backing_filename(bs, backing_filename,
                                    sizeof(backing_filename));
 
@@ -940,6 +936,19 @@  int bdrv_open_backing_file(BlockDriverState *bs, QDict *options)
     return 0;
 }
 
+/*
+ * Opens the backing file for a BlockDriverState if not yet open
+ *
+ * options is a QDict of options to pass to the block drivers, or NULL for an
+ * empty set of options. The reference to the QDict is transferred to this
+ * function (even on failure), so if the caller intends to reuse the dictionary,
+ * it needs to use QINCREF() before calling bdrv_file_open.
+ */
+int bdrv_open_backing_file(BlockDriverState *bs, QDict *options)
+{
+    return bdrv_open_backing_file_int(bs, options, NULL);
+}
+
 static void extract_subqdict(QDict *src, QDict **dst, const char *start)
 {
     const QDictEntry *entry, *next;
@@ -1056,7 +1065,7 @@  int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
         }
 
         if (total_size == -1) {
-            bs1 = bdrv_new_int("", NULL);
+            bs1 = bdrv_new_int("", NULL, NULL);
             ret = bdrv_open(bs1, filename, NULL, 0, drv);
             if (ret < 0) {
                 bdrv_delete(bs1);
@@ -1079,7 +1088,7 @@  int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
 
     extract_subqdict(options, &file_options, "file.");
     ret = bdrv_file_open_int(&file, filename, file_options,
-                             bdrv_open_flags(bs, flags), bs);
+                             bdrv_open_flags(bs, flags), bs, NULL);
     if (ret < 0) {
         goto fail;
     }
@@ -1109,7 +1118,7 @@  int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
         QDict *backing_options;
 
         extract_subqdict(options, &backing_options, "backing.");
-        ret = bdrv_open_backing_file(bs, backing_options);
+        ret = bdrv_open_backing_file_int(bs, backing_options, NULL);
         if (ret < 0) {
             goto close_and_fail;
         }