Using virtio_random

Bryan Venteicher bryanv at
Tue Sep 16 21:26:28 UTC 2014

On Mon, Sep 15, 2014 at 6:17 PM, John Nielsen <lists at> wrote:

> Hi all-
> I am happy to see that virtio_random(4) will be included in FreeBSD 10.1.
> To try it out, I loaded up BETA1 in a virtual machine with entropy
> passthrough enabled. After booting it with the virtio_random module loaded
> I see this in dmesg:
> virtio_pci3: <VirtIO PCI Entropy adapter> port 0xc0a0-0xc0bf irq 10 at
> device 6.0 on pci0
> vtrnd0: <VirtIO Entropy Adapter> on virtio_pci3
> virtio_pci3: host features: 0x71000000
> <EventIdx,RingIndirect,NotifyOnEmpty>
> virtio_pci3: negotiated features: 0
> So far, so good. (I think? The 'negotiated features: 0' gives me pause..)
The VirtIO random device is simple enough that's there is no benefit of the
offered features.

> Now how do I use the driver as an entropy source (or verify that it's
> being used)? I don't see any difference in the output of "sysctl
> kern.random" with or without the driver loaded. Is something missing?
The driver periodically (IIRC every 5 seconds) feeds random_harvest(9) with
random data from the host.

> Thanks,
> JN

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