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Date: Fri, 26 Oct 2012 20:59:54 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 2/4] virtio-rng-pci: create a default
 backend if none exists
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: Amit Shah <amit.shah@redhat.com>, qemu-devel@nongnu.org, Andreas Faerber <afaerber@suse.de>

Il 26/10/2012 19:21, Anthony Liguori ha scritto:
> This allows you to specify:
> 
>   $ qemu -device virtio-rng-pci
> 
> And things will Just Work with a reasonable default.
> 
> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
> ---
>  hw/virtio-pci.c | 13 +++++++++++++
>  hw/virtio-rng.h |  2 ++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index 0dc2a06..cfdb779 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -885,6 +885,19 @@ static int virtio_rng_init_pci(PCIDevice *pci_dev)
>      VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
>      VirtIODevice *vdev;
>  
> +    if (proxy->rng.rng == NULL) {
> +        proxy->rng.default_backend = RNG_RANDOM(object_new(TYPE_RNG_RANDOM));
> +
> +        object_property_add_child(OBJECT(pci_dev),
> +                                  "default-backend",
> +                                  OBJECT(proxy->rng.default_backend),
> +                                  NULL);
> +
> +        object_property_set_link(OBJECT(pci_dev),
> +                                 OBJECT(proxy->rng.default_backend),
> +                                 "rng", NULL);
> +    }
> +
>      vdev = virtio_rng_init(&pci_dev->qdev, &proxy->rng);
>      if (!vdev) {
>          return -1;
> diff --git a/hw/virtio-rng.h b/hw/virtio-rng.h
> index fbb0104..63ddb96 100644
> --- a/hw/virtio-rng.h
> +++ b/hw/virtio-rng.h
> @@ -13,12 +13,14 @@
>  #define _QEMU_VIRTIO_RNG_H
>  
>  #include "qemu/rng.h"
> +#include "qemu/rng-random.h"
>  
>  /* The Virtio ID for the virtio rng device */
>  #define VIRTIO_ID_RNG    4
>  
>  struct VirtIORNGConf {
>      RngBackend *rng;
> +    RndRandom *default_backend;
>  };
>  
>  #endif
> 

NACK.  Starting a guest that runs rngd (or just a malicious guest) will
completely deprive the host of entropy.

If you make the default /dev/hwrng, however, that would be ok.

Paolo