qemu: block: Add accessors for format layer node names

Introduce a set of accessors, which return node names based on
semantics. This will allow to us to modify how we setup the backing
chain in cases when e.g. the format driver can be omitted, without
breaking all the code.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/qemu/qemu_block.c

@@ -69,6 +69,23 @@ qemuBlockStorageSourceSetStorageNodename(virStorageSource *src,
 }
 
 
+/**
+ * qemuBlockStorageSourceSetFormatNodename:
+ * @src: virStorageSource to set the format nodename
+ * @nodename: The node name to set (stolen)
+ *
+ * Sets @nodename as the format node name of @src. Using NULL @nodename clears
+ * the nodename. @src takes ownership of @nodename.
+ */
+void
+qemuBlockStorageSourceSetFormatNodename(virStorageSource *src,
+                                        char *nodename)
+{
+    g_free(src->nodeformat);
+    src->nodeformat = nodename;
+}
+
+
 /**
  * qemuBlockStorageSourceGetEffectiveStorageNodename:
  * @src: virStorageSource to get the effective nodename of
@@ -100,6 +117,20 @@ qemuBlockStorageSourceGetStorageNodename(virStorageSource *src)
 }
 
 
+/**
+ * qemuBlockStorageSourceGetFormatNodename:
+ * @src: virStorageSource to get the effective nodename of
+ *
+ * Gets the nodename corresponding to the format layer. Useful when accessing
+ * format specific features. Returns NULL if there is no format layer.
+ */
+const char *
+qemuBlockStorageSourceGetFormatNodename(virStorageSource *src)
+{
+    return src->nodeformat;
+}
+
+
 /**
  * qemuBlockStorageSourceSupportsConcurrentAccess:
  * @src: disk storage source

src/qemu/qemu_block.h

@@ -30,12 +30,19 @@ void
 qemuBlockStorageSourceSetStorageNodename(virStorageSource *src,
                                          char *nodename);
 
+void
+qemuBlockStorageSourceSetFormatNodename(virStorageSource *src,
+                                        char *nodename);
+
 const char *
 qemuBlockStorageSourceGetEffectiveStorageNodename(virStorageSource *src);
 
 const char *
 qemuBlockStorageSourceGetStorageNodename(virStorageSource *src);
 
+const char *
+qemuBlockStorageSourceGetFormatNodename(virStorageSource *src);
+
 
 typedef struct qemuBlockNodeNameBackingChainData qemuBlockNodeNameBackingChainData;
 struct qemuBlockNodeNameBackingChainData {