virt-xml: Abide domain name for --build-xml

https://bugzilla.redhat.com/show_bug.cgi?id=1648939

man/virt-xml.pod

@@ -17,7 +17,7 @@ Each B<virt-xml> invocation requires 3 things: name of an existing domain to alt
 --add-device: Append a new device definition to the XML
 --remove-device: Remove an existing device definition
 --edit: Edit an existing XML block
---build-xml: Just build the requested XML block and print it (no domain or input XML are required here).
+--build-xml: Just build the requested XML block and print it. No domain or input are required here, but it's recommended to provide them, so virt-xml can fill in optimal defaults.
 
 An XML change is one instance of any of the XML options provided by virt-xml, for example --disk or --boot.
 
@@ -118,6 +118,8 @@ This option will error if specified with a non-device XML option (see --edit sec
 
 Just build the specified XML, and print it to stdout. No input domain or input XML is required. Example: '--build-xml --disk DISK-OPTIONS' will just print the new <disk> device.
 
+However if the generated XML is targeted for a specific domain, it's recommended to pass it to virt-xml, so the tool can set optimal defaults.
+
 This option will error if specified with an XML option that does not map cleanly to a specific XML block, like --vcpus or --memory.
 
 =back

tests/cli-test-xml/compare/virt-xml-build-disk-domain.xml

@@ -0,0 +1,5 @@
+<disk type="file" device="disk">
+  <driver name="qemu" type="qcow2"/>
+  <source file="/dev/default-pool/testvol1.img"/>
+  <target dev="vdaf" bus="virtio"/>
+</disk>

tests/cli-test-xml/compare/virt-xml-build-disk-plain.xml

@@ -0,0 +1,5 @@
+<disk type="file" device="disk">
+  <driver name="qemu" type="qcow2"/>
+  <source file="/dev/default-pool/testvol1.img"/>
+  <target dev="hda" bus="ide"/>
+</disk>

tests/clitest.py

@@ -1119,6 +1119,8 @@ c.add_compare("--build-xml --cpu pentium3,+x2apic", "build-cpu")
 c.add_compare("--build-xml --tpm path=/dev/tpm", "build-tpm")
 c.add_compare("--build-xml --blkiotune weight=100,device0.path=/dev/sdf,device.weight=200", "build-blkiotune")
 c.add_compare("--build-xml --idmap uid.start=0,uid.target=1000,uid.count=10,gid.start=0,gid.target=1000,gid.count=10", "build-idmap")
+c.add_compare("--connect %(URI-KVM)s --build-xml --disk %(EXISTIMG1)s", "build-disk-plain")
+c.add_compare("--connect %(URI-KVM)s test-many-devices --build-xml --disk %(EXISTIMG1)s", "build-disk-domain")
 c.add_compare("4a64cc71-19c4-2fd0-2323-3050941ea3c3 --edit --boot network,cdrom", "edit-bootorder")  # basic bootorder test, also using UUID lookup
 c.add_compare("--confirm 1 --edit --cpu host-passthrough", "prompt-response", input_text="yes")  # prompt response, also using domid lookup
 c.add_compare("--edit --print-diff --qemu-commandline clearxml=yes", "edit-clearxml-qemu-commandline", input_file=(XMLDIR + "/virtxml-qemu-commandline-clear.xml"))

virt-xml

@@ -217,14 +217,13 @@ def action_remove_device(guest, options, parserclass):
     return devs
 
 
-def action_build_xml(conn, options, parserclass):
+def action_build_xml(conn, options, parserclass, guest):
     if not parserclass.guest_propname:
         fail(_("--build-xml not supported for --%s") %
              parserclass.cli_arg_name)
     if options.os_variant is not None:
         fail(_("--os-variant is not supported with --build-xml"))
 
-    guest = virtinst.Guest(conn)
     inst = parserclass.lookup_prop(guest)
     if parserclass.prop_is_list(guest):
         inst = inst.new()
@@ -374,7 +373,8 @@ def parse_args():
         help=_("Add specified device. Example:\n"
         "--add-device --disk ..."))
     actg.add_argument("--build-xml", action="store_true",
-        help=_("Just output the built device XML, no domain required."))
+        help=_("Output built device XML. Domain is optional but "
+               "recommended to ensure optimal defaults."))
 
     outg = parser.add_argument_group(_("Output options"))
     outg.add_argument("--update", action="store_true",
@@ -467,8 +467,9 @@ def main(conn=None):
     if options.domain:
         domain, inactive_xmlobj, active_xmlobj = get_domain_and_guest(
             conn, options.domain)
-    elif not options.build_xml:
-        inactive_xmlobj = virtinst.Guest(conn, options.stdinxml)
+    else:
+        inactive_xmlobj = virtinst.Guest(conn,
+                parsexml=options.stdinxml)
 
     check_action_collision(options)
     parserclass = check_xmlopt_collision(options)
@@ -478,7 +479,7 @@ def main(conn=None):
              (parserclass.cli_arg_name))
 
     if options.build_xml:
-        devs = action_build_xml(conn, options, parserclass)
+        devs = action_build_xml(conn, options, parserclass, inactive_xmlobj)
         for dev in devs:
             # pylint: disable=no-member
             print_stdout(dev.get_xml())