Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754772Ab3ILMIk (ORCPT ); Thu, 12 Sep 2013 08:08:40 -0400 Received: from mail.eperm.de ([89.247.134.16]:36439 "EHLO mail.eperm.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752670Ab3ILMIi (ORCPT ); Thu, 12 Sep 2013 08:08:38 -0400 From: Stephan Mueller To: Geert Uytterhoeven Cc: "Theodore Ts'o" , LKML , dave.taht@bufferbloat.net Subject: Re: [PATCH] /dev/random: Insufficient of entropy on many architectures Date: Thu, 12 Sep 2013 14:08:28 +0200 Message-ID: <5896310.H6rEVunj63@tauon> User-Agent: KMail/4.10.5 (Linux/3.10.10-200.fc19.x86_64; KDE/4.10.5; x86_64; ; ) In-Reply-To: References: <10005394.BRCyBMYWy3@tauon> <2947789.S63SVUbC3N@tauon> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1409 Lines: 47 Am Donnerstag, 12. September 2013, 13:59:04 schrieb Geert Uytterhoeven: Hi Geert, >On Wed, Sep 11, 2013 at 8:49 AM, Stephan Mueller wrote: >> __u64 tmp = random_get_fast_cycles() - random_get_fast_cycles(); >> if(0 == tmp) >> >> return fail; >> >> return pass; > >That will fail if the cycle counter runs at less than say 4 times the >CPU clock... Well... > >BTW, I prefer a different name than "random_get_fast_cycles()", as it's >better to have something that returns different and unpredictable >numbers than an actual monotonic cycle counter. A monotonic counter is fully ok. Note, for /dev/random, the occurrence of events delivers entropy. Thus, we have to be able to precisely measure that occurrence. The timer itself does not need to deliver any entropy as long as it is fast. > >Gr{oetje,eeting}s, > > Geert > >-- >Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- >geert@linux-m68k.org > >In personal conversations with technical people, I call myself a >hacker. But when I'm talking to journalists I just say "programmer" or >something like that. -- Linus Torvalds Ciao Stephan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/