Hi Amos,

I'm a libvirt QE, and I can not understand the setting on libvirt.org for rng device.

Could you please help to explain a little?

(The xml in https://libvirt.org/formatdomain.html#elementsRng)

<backend model='random'>/dev/random</backend>

<source mode='bind' service='1234'/>

<source mode='connect' host='1.2.3.4' service='1234'/>

</backend>

</rng>

</devices>

How did it work with source mode='bind' and source mode='connect' together?

which process on guest or host will act as server part, which for client part?

One detail example:

start a vm with below device, and no egd running on host:

</backend>

</rng>

qemu command line:

-chardev udp,id=charrng0,host=127.0.0.1,port=1234,localaddr=,localport=1234 -object rng-egd,id=objrng0,chardev=charrng0 -device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x9

In my understanding the purpose of the rng device on guest is to provide guest a hardware RNG device /dev/hwrng which obtain seeds from the host.

The source can be /dev/random on host, then the xml will be:

<backend model='random'>/dev/random</backend>

</rng>

can be hardware on host:

<backend model='random'>/dev/hwrng</backend>

</rng>

can be edg daemon running on host:

</backend>

</rng>

(on host, there should be a egd daemon running on tcp 127.0.0.1:1234

# egd.pl --debug-client --nofork localhost:1234)

Thank you very much and look forward for your response!

-------
Best Regards,
Yalan Zhang
IRC: yalzhang
Internal phone: 8389413