conf: Introduce <shareable> for hostdev

Unlike disk device, the scsi-generic always writethrough the data,
so no need to introduce a "cache" tag, and set "cache=off".

docs/formatdomain.html.in

@@ -2506,6 +2506,12 @@
       <dd>Indicates that the device is readonly, only supported by SCSI host
         device now. <span class="since">Since 1.0.6 (QEMU and KVM only)</span>
       </dd>
+      <dt><code>shareable</code></dt>
+      <dd>If present, this indicates the device is expected to be shared
+        between domains (assuming the hypervisor and OS support this).
+        Only supported by SCSI host device.
+        <span class="since">Since 1.0.6</span>
+      </dd>
     </dl>
 
 

docs/schemas/domaincommon.rng

@@ -3135,6 +3135,11 @@
             <empty/>
           </element>
         </optional>
+        <optional>
+          <element name="shareable">
+            <empty/>
+          </element>
+        </optional>
       </interleave>
     </element>
   </define>