Re: [PATCHv2 2/8] doc: schema: Add basic documentation for the virtual RNG device support

Peter Krempa <pkrempa@xxxxxxxxxx> · Mon, 25 Feb 2013 10:08:50 +0100

On 02/22/13 19:20, Eric Blake wrote:
On 02/21/2013 07:47 AM, Peter Krempa wrote:
This patch documents XML elements used for (basic) support of virtual
RNG devices.

In the devices section in the domain XML users may specify:

For the default 'random' backend:
   <devices>
     <rng model='virtio'>
       <backend model='random'>/dev/urandom</backend>
     </rng>
   </devices>

For the slightly more advanced EGD backend:
   <devices>
     <rng model='virtio'>
       <backend model='egd' type='udp'>
         <!-- this is a definition of a character device -->
         <source mode='bind' service='1234'/>
         <source mode='connect' host='1.2.3.4' service='1234'/>
         <!-- or other valid character device configuration -->

You don't really allow two <source>; maybe a better layout would be a
strategic comment, such as:

       <backend model='egd' type='udp'>
         <!-- this is a definition of a character device -->
         <source mode='bind' service='1234'/>
         <!-- or other valid character device configuration, such as
         <source mode='connect' host='1.2.3.4' service='1234'/>
         -->

       </backend>
     </rng>
   </devices>

For the planned random daemon/pool:
   <devices>
     <rng model='virtio'>
       <backend model='pool' pool='poolname'>class</backend>

Missing </rng>

   </devices>

to enable the RNG device for guests.
---

Notes:
     Version 2:
     - ACKed, no change, unfortunately doesn't make sense to push alone

Still some nits to fix before pushing:

+<pre>
+  ...
+  &lt;devices&gt;
+    &lt;rng model='virtio'&gt;
+      &lt;backend model='random'&gt;/dev/random&lt;/backend&gt;
+      &lt;!-- OR --&gt;
+      &lt;backend model='egd' type='udp'&gt;
+        &lt;source mode='bind' service='1234'&gt;
+        &lt;source mode='connect' host='1.2.3.4' service='1234'&gt;
+      &lt;/backend&gt;
+    &lt;/rng&gt;
+  &lt;/devices&gt;
+  ...

Do we really want two <source> in a single <backend> in the example, or
would it be easier to show multiple <rng> devices, one for each type of
backend?

That actually is valid for the character device backends. The UDP 
backend has to use two separate sources for bi-directional 
communication. The definition of that source type is declared as a type 
in our RNG schema an I merely reused that.

+      <dd>
+        <p>
+          The <code>backend</code> element specifies the source of entropy
+          to be used for the doimain. The source model is configured using the

s/doimain/domain/

+          <code>model</code> attribute. Supported source models are:
+        </p>
+        <ul>
+          <li>'random' &mdash; /dev/random (default) or similar device as source</li>
+          <li>'egd' &mdash; a EGD protocol backend. </li>

not consistent on whether your <li> end with '.'

Peter

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