linux-kernel - Re: [PATCH] drivers/net: remove network drivers' last few uses of IRQF_SAMPLE

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Message-ID: <20080515222741.GQ18825@mit.edu>
Date:	Thu, 15 May 2008 18:27:41 -0400
From:	Theodore Tso <tytso@....edu>
To:	Jeff Garzik <jeff@...zik.org>
Cc:	Adrian Bunk <bunk@...nel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Chris Peterson <cpeterso@...terso.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mpm@...enic.com
Subject: Re: [PATCH] drivers/net: remove network drivers' last few uses of
	IRQF_SAMPLE_RANDOM

On Thu, May 15, 2008 at 06:04:04PM -0400, Jeff Garzik wrote:
>> I have seen embedded systems with zero entropy, and dubious entropy might 
>> there be better than no entropy at all.
>> Or am I wrong on the latter?
>
> It's also relevant to the discussion to note that input data to kernel 
> devrandom is mixed, and we can control the amount of "credit" applied to 
> incoming entropy.

Sure, and one possible thing to do is to simply always input the
interrupt information to the random number generator, but give it a
"entropy credit" of 0.  That has the net result of potentially
improving the entropy found in /dev/random and /dev/urandom, but not
necessarily compromising /dev/random, since /dev/random's output is
throttled by the entropy estimate.

The only cost of doing this would be the overhead in sending the
information into the entropy pool.

						- Ted
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