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Re: [Qemu-devel] [PATCH v2] rng-builtin: add an RNG backend that uses qe

From: Laurent Vivier
Subject: Re: [Qemu-devel] [PATCH v2] rng-builtin: add an RNG backend that uses qemu_guest_getrandom()
Date: Fri, 10 May 2019 17:56:29 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 10/05/2019 17:32, Daniel P. Berrangé wrote:
On Fri, May 10, 2019 at 02:37:41PM +0200, Laurent Vivier wrote:
On 10/05/2019 14:27, Markus Armbruster wrote:
Laurent Vivier <address@hidden> writes:
The new rng-builtin is considerably simpler than both rng-random and
rng-egd.  Moreover, it just works, whereas rng-random is limited to
CONFIG_POSIX, and rng-egd needs egd running (which I suspect basically
nobody does).  Have we considered deprecating these two backends in
favor of rng-builtin?

I have several bugzilla involving these backends: as there are blocking, the
virtio-rng device in the guest can hang, or crash during hot-unplug. From my
point of view, life would be easier without them...

Are you sure about that ?

The EGD impl looks like it is requesting entropy in an async manner.

The virtio-rng driver waits until it receives enough entropy from the RNG backend while a mutex is taken.

If the EGD daemon doesn't provide enough data to the RNG backend, virtio-rng driver can hang.

It's easy to have if we start EGD backend with a socket in server,nowait mode and no EGD daemon connects to the port.


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