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