docs: update zfs documentation

- docs/formatstorage.html.in: document 'zfs' pool type, add it
   to a list of pool types that could use source physical devices
 - docs/storage.html.in: update a ZFS pool example XML with
   source physical devices, mention that starting from 1.2.9 a
   pool could be created from this devices by libvirt and in earlier
   versions user still has to create a pool manually
 - docs/drvbhyve.html.in: add an example with ZFS pools

docs/drvbhyve.html.in

@@ -141,5 +141,21 @@ tweak them.</p>
 /usr/sbin/bhyve -c 2 -m 214 -A -I -H -P -s 0:0,hostbridge -s 3:0,virtio-net,tap0,mac=52:54:00:5d:74:e3 -s 2:0,virtio-blk,/home/user/vm1.img -s 1,lpc -l com1,/dev/nmdm0A vm1
 </pre>
 
+<h3><a name="zfsvolume">Using ZFS volumes</a></h3>
+
+<p>It's possible to use ZFS volumes as disk devices <span class="since">since 1.2.8</span>.
+An example of domain XML device entry for that will look like:</p>
+
+<pre>
+  ...
+  &lt;disk type='volume' device='disk'&gt;
+    &lt;source pool='zfspool' volume='vol1'/&gt;
+    &lt;target dev='vdb' bus='virtio'/&gt;
+  &lt;/disk&gt;
+  ...</pre>
+
+<p>Please refer to the <a href="storage.html">Storage documentation</a> for more details on storage
+management.</p>
+
   </body>
 </html>

docs/formatstorage.html.in

@@ -23,8 +23,9 @@
       (<span class="since">since 0.7.1</span>), <code>rbd</code>
       (<span class="since">since 0.9.13</span>), <code>sheepdog</code>
       (<span class="since">since 0.10.0</span>),
-      or <code>gluster</code> (<span class="since">since
-      1.2.0</span>). This corresponds to the
+      <code>gluster</code> (<span class="since">since
+      1.2.0</span>) or <code>zfs</code> (<span class="since">since
+      1.2.8</span>). This corresponds to the
       storage backend drivers listed further along in this document.
     </p>
     <h3><a name="StoragePoolFirst">General metadata</a></h3>
@@ -115,7 +116,7 @@
       <dt><code>device</code></dt>
       <dd>Provides the source for pools backed by physical devices
         (pool types <code>fs</code>, <code>logical</code>, <code>disk</code>,
-        <code>iscsi</code>).
+        <code>iscsi</code>, <code>zfs</code>).
         May be repeated multiple times depending on backend driver. Contains
         a single attribute <code>path</code> which is the fully qualified
         path to the block device node. <span class="since">Since 0.4.1</span></dd>

docs/storage.html.in

@@ -750,22 +750,28 @@
     <p>
       This provides a pool based on the ZFS filesystem. It is currently
       supported on FreeBSD only.
-
-      A pool has to be created before libvirt could start using it. That
-      could be done using <code>zpool create</code> command. Please refer to
-      the ZFS documentation for details on a pool creation.
-
-      <span class="since">Since 1.2.8</span>
     </p>
 
+    <p>A pool could either be created manually using the <code>zpool create</code>
+      command and its name specified in the source section or <span class="since">
+      since 1.2.9</span> source devices could be specified to create a pool using
+      libvirt.
+    </p>
+
+    <p>Please refer to the ZFS documentation for details on a pool creation.</p>
+
+    <p><span class="since">Since 1.2.8</span></p>.
+
     <h3>Example pool input</h3>
     <pre>
       &lt;pool type="zfs"&gt;
         &lt;name&gt;myzfspool&lt;/name&gt;
         &lt;source&gt;
           &lt;name&gt;zpoolname&lt;/name&gt;
+          &lt;device path="/dev/ada1"/&gt;
+          &lt;device path="/dev/ada2"/&gt;
         &lt;/source&gt;
-       &lt;/pool&gt;</pre>
+      &lt;/pool&gt;</pre>
 
     <h3>Valid pool format types</h3>
     <p>