linux-kernel - Re: [PATCH 2/2] lguest: virtio-rng support

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Date:	Fri, 16 May 2008 13:25:09 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Johannes Berg <johannes@...solutions.net>
CC:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	Jeff Garzik <jeff@...zik.org>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] lguest: virtio-rng support

Johannes Berg wrote:
>> +
>> +/* Our random number generator device reads from /dev/urandom into the Guest's
>> + * input buffers.  The usual case is that the Guest doesn't want random numbers
>> + * and so has no buffers although /dev/urandom is still readable, whereas
>> + * console is the reverse.
> 
> Is it really a good idea to use the hosts /dev/urandom to fill the
> guests /dev/random?

Only if you have an entropy estimate to go with it.  It's still dubious, 
though: the guests own pool will do its own mixing, so you might as well 
pull from /dev/random in the host as being a genuine entropy source and 
only add what entropy is available.

	-hpa
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