Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754289Ab3ILMPh (ORCPT ); Thu, 12 Sep 2013 08:15:37 -0400 Received: from mail-pa0-f47.google.com ([209.85.220.47]:33315 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752312Ab3ILMPf (ORCPT ); Thu, 12 Sep 2013 08:15:35 -0400 MIME-Version: 1.0 In-Reply-To: <5896310.H6rEVunj63@tauon> References: <10005394.BRCyBMYWy3@tauon> <2947789.S63SVUbC3N@tauon> <5896310.H6rEVunj63@tauon> Date: Thu, 12 Sep 2013 14:15:35 +0200 X-Google-Sender-Auth: RE9yCy6bH5Fvz275GAWAOSegLoI Message-ID: Subject: Re: [PATCH] /dev/random: Insufficient of entropy on many architectures From: Geert Uytterhoeven To: Stephan Mueller Cc: "Theodore Ts'o" , LKML , dave.taht@bufferbloat.net Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1508 Lines: 36 On Thu, Sep 12, 2013 at 2:08 PM, Stephan Mueller wrote: >>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. Well, in my specific case (m68k/Amiga) I can use: - a 24-bit counter running at only ca. 15 or 31 kHz (actual frequency may vary), - a 16-bit counter running at ca. 700 kHz. That is, if they have to be monotonic cycle counters. If not, I can mix the two (e.g. "a << 8 | (b & 0xff)") to get a 32-bit value. That result would be fine for /dev/random, I guess, but it's not really "get_cycles()". 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 -- 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/