[Qemu-devel] [PATCH 0/8] add paravirtualization hwrng support (v3)

[Anthony Liguori <aliguori@us.ibm.com>]

Hi,

This series implements the backend and frontend infrastructure for virtio-rng.
This is similar to previous series sent out by both Amit and myself although
it has been trimmed down considerably.

In terms of backends, a file and EGD backend are supported.  The file defaults
to /dev/random based on the feedback from Peter.  It's still possible to
support /dev/urandom though as an entropy source by overriding the file name.

v1 -> v2:
 - Include default backend patch from separate series
 - Add a rate limiting patch
v2 -> v3:
 - Small bug fix spotted by Paolo

My take away from all of the various discussions on what the Right Way to
use virtio-rng is:

 1) /dev/random should always be used as the entropy source (I've left it
    configurable though)

 2) I think the Right Way to configure virtio-rng is to figure out what the
    available entropy is on the host, and then decide how to allocate that
    to each guest.  As such, I've implemented rate limiting.

    I think QEMU is the right place to do this because this is a property of
    specific virtual machines.  I can imagine a cloud provider wanting to
    guarantee a certain level of entropy for different classes of VMs.  Even
    if rngd could be used to do this, configuring it differently for different
    guests would be cumbersome.

 3) `qemu -device virtio-rng-pci` will Just Work but risks exhausting host
    entropy.  This means we can't make it the default for machines.  But for
    most command line users, I think this is the behavior they want.