virt-xml: Disable clearxml= for devices

It doesn't work in the general case, and users can just --remove and
--add devices as needed for the same effect

man/virt-xml.pod

@@ -62,7 +62,7 @@ Edit the specified XML block. EDIT-OPTIONS tell B<virt-xml> which block to edit.
 
 Certain XML options only ever map to a single XML block, like --cpu, --security, --boot, --clock, and a few others. In those cases, B<virt-xml> will not complain if a corresponding XML block does not already exist, it will create it for you.
 
-Every XML option has a special value 'clearxml=yes'. When combined with --edit, it will completely blank out the XML block being edited before applying the requested changes. This allows completely rebuilding an XML block. See EXAMPLES for some usage.
+Some XML option support a special value 'clearxml=yes'. When combined with --edit, it will completely blank out the XML block being edited before applying the requested changes. This allows completely rebuilding an XML block. See EXAMPLES for some usage.
 
 EDIT-OPTIONS examples:
 
@@ -230,8 +230,6 @@ Generally these options map pretty straightforwardly to the libvirt XML, documen
 
 Option strings are in the format of: --option opt=val,opt2=val2,...  example: --disk path=/tmp/foo,shareable=on. Properties can be used with '--option opt=,', so to clear a disks cache setting you could use '--disk cache=,'
 
-Every XML option has a special value 'clearxml=yes'. When combined with --edit, it will completely blank out the XML block being edited before applying the requested changes. This allows completely rebuilding an XML block. See EXAMPLES for some usage.
-
 For any option, use --option=? to see a list of all available sub options, example: --disk=?  or  --boot=?
 
 --help output also lists a few general examples. See the EXAMPLES section below for some common examples.

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

@@ -1,16 +0,0 @@
-   </pm>
-   <devices>
-     <emulator>/usr/lib/xen/bin/qemu-dm</emulator>
--    <disk type="block" device="floppy">
--      <source dev="/dev/null"/>
-+    <disk device="floppy">
-       <target dev="fda" bus="fdc"/>
--      <boot order="5"/>
--      <address type="drive" controller="0" bus="0" target="0" unit="0"/>
-+      <source file="/foo/bar"/>
-     </disk>
-     <disk type="dir" device="floppy">
-       <source dir="/tmp"/>
-
-Domain 'test-many-devices' defined successfully.
-Changes will take effect after the next domain shutdown.

tests/clitest.py

@@ -844,9 +844,9 @@ c.add_compare("--edit mac=00:11:7f:33:44:55 --network target=nic55", "edit-selec
 
 c = vixml.add_category("edit clear", "test-many-devices --print-diff --define", compare_check=support.SUPPORT_CONN_INPUT_KEYBOARD)
 c.add_invalid("--edit --memory 200,clearxml=yes")  # clear isn't wired up for memory
+c.add_invalid("--edit --disk /foo/bar,target=fda,bus=fdc,device=floppy,clearxml=yes")  # clearxml isn't supported for devices
 c.add_compare("--edit --cpu host-passthrough,clearxml=yes", "edit-clear-cpu")
 c.add_compare("--edit --clock offset=utc,clearxml=yes", "edit-clear-clock")
-c.add_compare("--edit --disk /foo/bar,target=fda,bus=fdc,device=floppy,clearxml=yes", "edit-clear-disk")
 
 c = vixml.add_category("add/rm devices", "test-many-devices --print-diff --define", compare_check=support.SUPPORT_CONN_INPUT_KEYBOARD)
 c.add_invalid("--add-device --security foo")  # --add-device without a device

virtinst/cli.py

@@ -948,16 +948,12 @@ class VirtCLIParser(object):
     def __init_global_params(self):
         def set_clearxml_cb(opts, inst, cliname, val):
             ignore = opts = cliname
-            if not self.clear_attr and not self.devclass:
+            if not self.clear_attr:
                 raise RuntimeError("Don't know how to clearxml --%s" %
                                    self.cli_arg_name)
-
-            clearobj = inst
-            if self.clear_attr:
-                clearobj = getattr(inst, self.clear_attr)
             if val is not True:
                 return
-            clearobj.clear()
+            getattr(inst, self.clear_attr).clear()
 
         self.set_param(None, "clearxml",
                        setter_cb=set_clearxml_cb, is_onoff=True)