@@ -268,6 +268,62 @@ enum {
DEFAULT_PERM_UNCHANGED = BLK_PERM_ALL & ~DEFAULT_PERM_PASSTHROUGH,
};
+/*
+ * Flags that parent nodes assign to child nodes to specify what kind of
+ * role(s) they take.
+ *
+ * At least one of DATA, METADATA, FILTERED, or COW must be set for
+ * every child.
+ */
+enum BdrvChildRoleBits {
+ /*
+ * This child stores data.
+ * Any node may have an arbitrary number of such children.
+ */
+ BDRV_CHILD_DATA = (1 << 0),
+
+ /*
+ * This child stores metadata.
+ * Any node may have an arbitrary number of metadata-storing
+ * children.
+ */
+ BDRV_CHILD_METADATA = (1 << 1),
+
+ /*
+ * A child that always presents exactly the same visible data as
+ * the parent, e.g. by virtue of the parent forwarding all reads
+ * and writes.
+ * This flag is mutually exclusive with DATA, METADATA, and COW.
+ * Any node may have at most one filtered child at a time.
+ */
+ BDRV_CHILD_FILTERED = (1 << 2),
+
+ /*
+ * Child from which to read all data that isn’t allocated in the
+ * parent (i.e., the backing child); such data is copied to the
+ * parent through COW (and optionally COR).
+ * This field is mutually exclusive with DATA, METADATA, and
+ * FILTERED.
+ * Any node may have at most one such backing child at a time.
+ */
+ BDRV_CHILD_COW = (1 << 3),
+
+ /*
+ * The primary child. For most drivers, this is the child whose
+ * filename applies best to the parent node.
+ * Any node may have at most one primary child at a time.
+ */
+ BDRV_CHILD_PRIMARY = (1 << 4),
+
+ /* Useful combination of flags */
+ BDRV_CHILD_IMAGE = BDRV_CHILD_DATA
+ | BDRV_CHILD_METADATA
+ | BDRV_CHILD_PRIMARY,
+};
+
+/* Mask of BdrvChildRoleBits values */
+typedef unsigned int BdrvChildRole;
+
char *bdrv_perm_names(uint64_t perm);
uint64_t bdrv_qapi_perm_to_blk_perm(BlockPermission qapi_perm);