Message-ID: <507CE663.2060502@linux.intel.com>
Date: Mon, 15 Oct 2012 21:45:23 -0700
From: "H. Peter Anvin" <hpa@linux.intel.com>
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To: "Theodore Ts'o" <tytso@mit.edu>, "H. Peter Anvin" <hpa@zytor.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        greg@kroah.com, w@1wt.eu, ewust@umich.edu, zakir@umich.edu,
        mpm@selenic.com, nadiah@cs.ucsd.edu, jhalderm@umich.edu,
        tglx@linutronix.de, davem@davemloft.net, mingo@kernel.org,
        DJ Johnston <dj.johnston@intel.com>, stable@vger.kernel.org
Subject: Re: [PATCH RFC] random: Account for entropy loss due to overwrites
References: <1344878779-10700-1-git-send-email-hpa@linux.intel.com> <50675038.9000108@zytor.com> <20121016040848.GE17446@thunk.org>
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On 10/15/2012 09:08 PM, Theodore Ts'o wrote:
> On Sat, Sep 29, 2012 at 12:47:04PM -0700, H. Peter Anvin wrote:
>>> -static struct poolinfo {
>>> +static const struct poolinfo {
>>> +	int poolshift;		/* log2(POOLBITS) */
>>>  	int poolwords;
>>>  	int tap1, tap2, tap3, tap4, tap5;
> 
> Poolshift is duplicated information; it's just log2(poolwords) + 5
> (since POOLBITS is poolwords*32).
> 
> Granted you don't want to recalculate it every single time you need to
> use it, but perhaps it would be better to add poolshift to struct
> entropy_store, and set it in init_std_data()?
> 

Or we could compute poolwords (and poolbits, and poolbytes) from it,
since shifts generally are cheap.  I don't strongly care, whatever your
preference is.

	-hpa


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