util: storage: Add helpers to parse and format relPath into privateData

This will be the first private piece of data that will need to be stored
in the XML for some drivers. Add helpers which will do it.

src/libvirt_private.syms

@@ -2734,6 +2734,8 @@ virStorageSourceParseRBDColonString;
 virStorageSourcePoolDefFree;
 virStorageSourcePoolModeTypeFromString;
 virStorageSourcePoolModeTypeToString;
+virStorageSourcePrivateDataFormatRelPath;
+virStorageSourcePrivateDataParseRelPath;
 virStorageSourceUpdateBackingSizes;
 virStorageSourceUpdateCapacity;
 virStorageSourceUpdatePhysicalSize;

src/util/virstoragefile.c

@@ -4086,3 +4086,23 @@ virStorageSourceNetworkAssignDefaultPorts(virStorageSourcePtr src)
             src->hosts[i].port = virStorageSourceNetworkDefaultPort(src->protocol);
     }
 }
+
+
+int
+virStorageSourcePrivateDataParseRelPath(xmlXPathContextPtr ctxt,
+                                        virStorageSourcePtr src)
+{
+    src->relPath = virXPathString("string(./relPath)", ctxt);
+    return 0;
+}
+
+
+int
+virStorageSourcePrivateDataFormatRelPath(virStorageSourcePtr src,
+                                         virBufferPtr buf)
+{
+    if (src->relPath)
+        virBufferEscapeString(buf, "<relPath>%s</relPath>\n", src->relPath);
+
+    return 0;
+}

src/util/virstoragefile.h

@@ -441,4 +441,12 @@ bool
 virStorageSourceHasBacking(const virStorageSource *src);
 
 
+int
+virStorageSourcePrivateDataParseRelPath(xmlXPathContextPtr ctxt,
+                                        virStorageSourcePtr src);
+int
+virStorageSourcePrivateDataFormatRelPath(virStorageSourcePtr src,
+                                         virBufferPtr buf);
+
+
 #endif /* __VIR_STORAGE_FILE_H__ */