xmlbuilder: Support clear()ing an object in place

This gives friendly XML output via virt-xml for clearxml=yes +
extra options: the XML block is editted in place, rather than removed
and with the newchanges appended

tests/cli-test-xml/compare/virt-xml-edit-clear-clock.xml

@@ -1,20 +1,12 @@
-     <feature policy="require" name="xtpr"/>
      <feature policy="require" name="acpi"/>
    </cpu>
--  <clock offset="utc">
+   <clock offset="utc">
 -    <timer name="rtc" tickpolicy="catchup"/>
 -    <timer name="pit" tickpolicy="delay"/>
 -    <timer name="hpet" present="no"/>
--  </clock>
+   </clock>
    <on_poweroff>destroy</on_poweroff>
    <on_reboot>restart</on_reboot>
-   <on_crash>restart</on_crash>
-@@
-     </panic>
-   </devices>
-   <seclabel type="dynamic" model="selinux" relabel="yes"/>
-+  <clock offset="utc"/>
- </domain>
 
 Domain 'test-for-virtxml' defined successfully.
 Changes will take effect after the next domain shutdown.

tests/cli-test-xml/compare/virt-xml-edit-clear-cpu.xml

@@ -17,16 +17,10 @@
 -    <feature policy="require" name="ds_cpl"/>
 -    <feature policy="require" name="xtpr"/>
 -    <feature policy="require" name="acpi"/>
--  </cpu>
++  <cpu mode="host-passthrough">
+   </cpu>
    <clock offset="utc">
      <timer name="rtc" tickpolicy="catchup"/>
-     <timer name="pit" tickpolicy="delay"/>
-@@
-     </panic>
-   </devices>
-   <seclabel type="dynamic" model="selinux" relabel="yes"/>
-+  <cpu mode="host-passthrough"/>
- </domain>
 
 Domain 'test-for-virtxml' defined successfully.
 Changes will take effect after the next domain shutdown.

virtinst/cli.py

@@ -1028,17 +1028,27 @@ class VirtCLIParser(object):
 
     def __init_global_params(self):
         def set_clearxml_cb(opts, inst, cliname, val):
-            ignore = opts = cliname
+            ignore = opts
+            ignore = cliname
             if not self.objclass and not self.clear_attr:
                 raise RuntimeError("Don't know how to clearxml --%s" %
                                    self.cli_arg_name)
             if val is not True:
                 return
 
+            clear_inst = inst
             if self.clear_attr:
-                getattr(inst, self.clear_attr).clear()
+                clear_inst = getattr(inst, self.clear_attr)
-            else:
+
-                inst.clear()
+            # If there's any opts remaining, leave the root stub element
+            # in place, so virt-xml updates are done in place.
+            #
+            # So --edit --cpu clearxml=yes  should remove the entire <cpu>
+            # block. But --edit --cpu clearxml=yes,model=foo should leave
+            # a <cpu> stub in place, so that it gets model=foo in place,
+            # otherwise the newly created cpu block gets appened to the
+            # end of the domain XML, which gives an ugly diff
+            clear_inst.clear(leave_stub=bool(opts.opts))
 
         self.set_param(None, "clearxml",
                        setter_cb=set_clearxml_cb, is_onoff=True)

virtinst/support.py

@@ -312,9 +312,9 @@ SUPPORT_CONN_MEM_STATS_PERIOD = _make(
     function="virDomain.setMemoryStatsPeriod",
     version="1.1.1", hv_version={"qemu": 0})
 SUPPORT_CONN_SPICE_GL = _make(version="1.3.3",
-    hv_version={"qemu": "2.5.92", "test": 0})
+    hv_version={"qemu": "2.7.92", "test": 0})
 SUPPORT_CONN_VIDEO_VIRTIO_ACCEL3D = _make(version="1.3.0",
-    hv_version={"qemu": "2.5.0", "test": 0})
+    hv_version={"qemu": "2.7.0", "test": 0})
 
 
 # This is for disk <driver name=qemu>. xen supports this, but it's

virtinst/xmlbuilder.py

@@ -38,6 +38,10 @@ _trackprops = bool("VIRTINST_TEST_SUITE" in os.environ)
 _allprops = []
 _seenprops = []
 
+# Convenience global to prevent _remove_xpath_node from unlinking the
+# top relavtive node in certain cases
+_top_node = None
+
 
 class _DocCleanupWrapper(object):
     def __init__(self, doc):
@@ -224,17 +228,17 @@ def _remove_xpath_node(ctx, xpath, dofree=True):
             if not is_orig:
                 continue
 
+        if node == root_node or node == _top_node:
+            # Don't unlink the root node, since it's spread out to all
+            # child objects and it ends up wreaking havoc.
+            break
+
         # Look for preceding whitespace and remove it
         white = node.get_prev()
         if white and white.type == "text" and not white.content.count("<"):
             white.unlinkNode()
             white.freeNode()
 
-        if node == root_node:
-            # Don't unlink the root node, since it's spread out to all
-            # child objects and it ends up wreaking havoc.
-            break
-
         node.unlinkNode()
         if dofree:
             node.freeNode()
@@ -836,17 +840,28 @@ class XMLBuilder(object):
         finally:
             self._finish_get_xml(data)
 
-    def clear(self):
+    def clear(self, leave_stub=False):
         """
         Wipe out all properties of the object
+
+        :param leave_stub: if True, don't unlink the top stub node,
+            see virtinst/cli usage for an explanation
         """
+        global _top_node
+        old_top_node = _top_node
+        try:
+            if leave_stub:
+                _top_node = _get_xpath_node(self._xmlstate.xml_ctx,
+                                            self.get_root_xpath())
             props = self._all_xml_props().values()
             props += self._all_child_props().values()
             for prop in props:
                 prop.clear(self)
+        finally:
+            _top_node = old_top_node
 
         is_child = bool(re.match("^.*\[\d+\]$", self.get_root_xpath()))
-        if is_child:
+        if is_child or leave_stub:
             # User requested to clear an object that is the child of
             # another object (xpath ends in [1] etc). We can't fully remove
             # the node in that case, since then the xmlbuilder object is
@@ -855,6 +870,7 @@ class XMLBuilder(object):
             node = _get_xpath_node(self._xmlstate.xml_ctx,
                                    self.get_root_xpath())
             indent = 2 * self.get_root_xpath().count("/")
+            if node:
                 node.setContent("\n" + (indent * " "))
         else:
             _remove_xpath_node(self._xmlstate.xml_ctx,