domain.rng vs. formatdomain.html#elementsUSB

The Relax-NG schema for domains regarding <hostdev> doesn't match what's
implemented in src/conf/domain_conf.c#virDomainHostdevDefFormat(): The
implementation only requires @type, but the schema currently either
required none or all three attributes (@mode, @type, and @managed) to be
defined together, because they are declared in the same
<optional)-section. (@managed is currently even undocumented on
<http://libvirt.org/formatdomain.html#elementsUSB>).

Thus the following minimal <hostdev>-example fails to validate:
<domain type='test'>
        <name>N</name>
        <memory>4096</memory>
        <bootloader>/bin/false</bootloader>
        <os>
                <type arch='x86_64' machine='xenpv'>linux</type>
        </os>
        <devices>
                <hostdev type='pci'>
                        <source>
                                <address bus='0x06' slot='0x00' function='0x0'/>
                        </source>
                </hostdev>
        </devices>
</domain>

The schema is changed to match the current implementation:
1. @mode is optional (which defaults to 'subsystem')
2. @type is required
3. @managed is optional (which defaults to 'no')

The documentation is updated to mention @managed.
Signed-off-by: NPhilipp Hahn <hahn@univention.de>

docs/formatdomain.html.in

@@ -954,7 +954,7 @@
 <pre>
   ...
   &lt;devices&gt;
-    &lt;hostdev mode='subsystem' type='pci'&gt;
+    &lt;hostdev mode='subsystem' type='pci' managed='yes'&gt;
       &lt;source&gt;
         &lt;address bus='0x06' slot='0x02' function='0x0'/&gt;
       &lt;/source&gt;
@@ -966,9 +966,11 @@
     <dl>
       <dt><code>hostdev</code></dt>
       <dd>The <code>hostdev</code> element is the main container for describing
-      host devices. For usb device passthrough <code>mode</code> is always
-      "subsystem" and <code>type</code> is "usb" for an USB device and "pci"
-      for a PCI device..
+        host devices. For usb device passthrough <code>mode</code> is always
+        "subsystem" and <code>type</code> is "usb" for a USB device and "pci"
+        for a PCI device. When <code>managed</code> is "yes" for a PIC
+        device, it is detached from the host before being passed on to
+        the guest.</dd>
       <dt><code>source</code></dt>
       <dd>The source element describes the device as seen from the host.
       The USB device can either be addressed by vendor / product id using the

docs/schemas/domain.rng

@@ -1731,12 +1731,14 @@
             <value>capabilities</value>
           </choice>
         </attribute>
-        <attribute name="type">
-          <choice>
-            <value>usb</value>
-            <value>pci</value>
-          </choice>
-        </attribute>
+      </optional>
+      <attribute name="type">
+        <choice>
+          <value>usb</value>
+          <value>pci</value>
+        </choice>
+      </attribute>
+      <optional>
         <attribute name="managed">
           <choice>
             <value>yes</value>