4:27 p.m.
On 01/11/2013 10:00 AM, Peter Krempa wrote:
This patch documments XML elements used for (basic) support of
virtual
s/documments/documents/
RNG devices.
In the devices section in the domain XML users may specify:
<devices>
<rng model='none'/>
Do we need model='none'? Historically, we have added it for devices
where the device used to be always-on by default, but we didn't have XML
for the device, then later on the device became optional so we had to
have a way to express the absence of the device without breaking
back-compat of old XML that gets the default for free. But in the case
of rng, I don't think we currently have any device for free, so
model='none' doesn't seem to add anything.
</devices>
and the more useful variant:
<devices>
<rng model='virtio'>
<source type='random'>/dev/urandom</source>
</rng>
</devices>
This part, however, seems reasonable.
---
docs/formatdomain.html.in | 54 +++++++++++++++++++++++++++++++++++++++++++
docs/schemas/domaincommon.rng | 31 +++++++++++++++++++++++++
2 files changed, 85 insertions(+)
diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index bb0b199..7a5f267 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -4260,6 +4260,60 @@ qemu-kvm -net nic,model=? /dev/null
</ul>
</dd>
</dl>
+ <h4><a name="elementsRng">Random number generator
device</a></h4>
+
+ <p>
+ The virtual random number generator device allows the host to pass
+ through entropy to guest operating systems.
+ <span class="since">Since 1.0.2</span>
Yikes - our delay in reviewing this means that it might not make 1.0.2
after all. It's probably a good sign that the list is now getting so
many patches, but at the same time it points out that everyone needs to
help more with reviews.
+ <dt><code>model</code></dt>
+ <dd>
+ <p>
+ The required <code>model</code> attribute specifies what type
+ of RNG device is provided. Valid values are specific to
+ the virtualization platform:
+ </p>
+ <ul>
+ <li>'none' — disable the rng device</li>
Again, isn't omitting the <rng> element sufficient for this task?
+ <li>'virtio' — supported by qemu
and virtio-rng kernel module</li>
+ </ul>
+ </dd>
+ <dt><code>source</code></dt>
+ <dd>
+ <p>
+ The <code>source</code> element specifies the source of entropy
+ to be used for the doimain. The source type is configured using the
s/doimain/domain/
+ <code>type</code> attribute. Supported source
types are:
+ </p>
+ <ul>
+ <li>'none' — no source was configured</li>
+ <li>'random' — /dev/random or similar device as
source</li>
Here, it _does_ make sense to expose both a type='none' and
type='random'; assuming that qemu has a default source of entropy that
it uses when libvirt doesn't specify one.
+ </ul>
+ </dd>
+ <dt><code>source type='random'</code></dt>
+ <dd>
+ <p>
+ This source type expects a non-blocking character device as input.
+ Examples of such devices are /dev/random and /dev/urandom. The file
+ name is specified as contents of the <code>source</code> element.
Side question - is it also possible to pass a (large) regular file, so
that you can experiment with reproducible random replays? At least with
coreutil's 'shuf --random-source', it is indeed possible to replay a
particular byte stream (obviously, on reply, the element of true
randomness is gone, but for analysis purposes, it can still be a useful
thing to do).
I guess what this means for libvirt is that we should allow whatever
file name the user passes, rather than actually stat()ing the file and
enforcing that it be a char device.
+ <define name="rng">
+ <element name="rng">
+ <attribute name="model">
+ <choice>
+ <value>none</value>
+ <value>virtio</value>
+ </choice>
Again, not sure we need this level of <choice>.
+ </attribute>
+ </element>
+ </define>
+
+ <define name="rng-source">
+ <element name="source">
+ <choice>
+ <group>
+ <attribute name="type">
+ <value>none</value>
+ </attribute>
+ <empty/>
+ </group>
+ <group>
+ <attribute name="type">
+ <value>random</value>
+ </attribute>
+ <ref name="filePath"/>
+ </group>
+ </choice>
+ </element>
+ </define>
This part looks fine.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org