Authors:

avatar of Jakub Niedermertl

Jakub Niedermertl

Feature pages are design documents that developers have created while collaborating on oVirt.

Most of them are outdated, but provide historical design context.

They are not user documentation and should not be treated as such.

Documentation is available here.

Virtio RNG Enhancements

Owner

urandom replaces random

Summary

/dev/urandom random number generator (RNG) source replace /dev/random for VMs with effective compatibility version >= 4.1. urandom presents a non-blocking (“unlimited”) rng source as opposed to random.

Related bug.

Engine

Each time VM effective compatibility level is changed (by change of cluster compatibility level or VM custom compatibility level) source of rng generator device is checked and updated if necessary.

Non-cluster Entities

For non-cluster-aware entities (Blank template and instance types) urandom and random rng sources are united to one rng source labeled “urandom or random” in UI and urandom in REST api. Such rng source will be differentiated to either urandom or random (depending of effective compatibility level) when Blank template or instance type will be applied to a new VM.

Compatibility

Host machines require libvirt version >= 1.3.4. (i.e. RHEL/CentOS >= 7.3) to support urandom rng source.

urandom or random rng enable by default

Summary

  • All clusters in engine v4.1 requires that their hosts provide /dev/urandom or /dev/random rng device for cluster compatibility level 4.1+ or 4.0- respectively.
  • Blank template and predefined instance types now contains “urandom or random” based rng device. Thus new VMs based on these entities will contain such rng device.

Related bug.

REST Api

List of rng sources that cluster requires for all its hosts is available in cluster/required_rng_sources. Source urandom or random is always present and can’t be removed.

GET ovirt-engine/api/clusters/{clusterId}

<cluster>
    ...
    <required_rng_sources>
        <required_rng_source>urandom</required_rng_source>
    </required_rng_sources>
</cluster>