secret: add iscsi to possible usage types

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/formatsecret.html.in

@@ -66,6 +66,18 @@
       device</a>. <span class="since">Since 0.9.7</span>.
     </p>
 
+    <h3>Usage type "iscsi"</h3>
+
+    <p>
+      This secret is associated with an iSCSI target for CHAP authentication.
+      The <code>&lt;usage type='iscsi'&gt;</code> element must contain
+      a single <code>target</code> element that specifies a usage name
+      for the secret.  The iSCSI secret can then be used by UUID or by
+      this usage name via the <code>&lt;auth&gt;</code> element of
+      a <a href="domain.html#elementsDisks">disk
+      device</a>. <span class="since">Since 1.0.4</span>.
+    </p>
+
     <h2><a name="example">Example</a></h2>
 
     <pre>

docs/schemas/secret.rng

@@ -41,6 +41,7 @@
             <choice>
               <ref name='usagevolume'/>
               <ref name='usageceph'/>
+              <ref name='usageiscsi'/>
               <!-- More choices later -->
             </choice>
           </element>
@@ -67,4 +68,13 @@
     </element>
   </define>
 
+  <define name='usageiscsi'>
+    <attribute name='type'>
+      <value>iscsi</value>
+    </attribute>
+    <element name='target'>
+      <ref name='genericName'/>
+    </element>
+  </define>
+
 </grammar>