linux-kernel - Re: [PATCH RFC] random: Account for entropy loss due to overwrites

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Message-ID: <20121016040848.GE17446@thunk.org>
Date:	Tue, 16 Oct 2012 00:08:48 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	greg@...ah.com, w@....eu, ewust@...ch.edu, zakir@...ch.edu,
	mpm@...enic.com, nadiah@...ucsd.edu, jhalderm@...ch.edu,
	tglx@...utronix.de, davem@...emloft.net, mingo@...nel.org,
	DJ Johnston <dj.johnston@...el.com>, stable@...r.kernel.org
Subject: Re: [PATCH RFC] random: Account for entropy loss due to overwrites

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()?

				- Ted
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