From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755001AbXLFQK7 (ORCPT ); Thu, 6 Dec 2007 11:10:59 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752635AbXLFQKv (ORCPT ); Thu, 6 Dec 2007 11:10:51 -0500 Received: from waste.org ([66.93.16.53]:60107 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752998AbXLFQKu (ORCPT ); Thu, 6 Dec 2007 11:10:50 -0500 Date: Thu, 6 Dec 2007 10:09:50 -0600 From: Matt Mackall To: Eric Dumazet Cc: Alan Cox , Adrian Bunk , Marc Haber , linux-kernel@vger.kernel.org, "David S. Miller" Subject: Re: Why does reading from /dev/urandom deplete entropy so much? Message-ID: <20071206160950.GX19691@waste.org> References: <20071204114125.GA17310@torres.zugschlus.de> <20071204161811.GB15974@stusta.de> <20071204164720.6e4dc2c4@the-village.bc.nu> <475599D6.4030008@cosmosbay.com> <20071205212646.GP17536@waste.org> <47579E89.6080802@cosmosbay.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <47579E89.6080802@cosmosbay.com> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 06, 2007 at 08:02:33AM +0100, Eric Dumazet wrote: > Matt Mackall a ?crit : > >On Tue, Dec 04, 2007 at 07:17:58PM +0100, Eric Dumazet wrote: > >>Alan Cox a ?crit : > >>>>No matter what you consider as being better, changing a 12 years old > >>>>and widely used userspace interface like /dev/urandom is simply not an > >>>>option. > >>>> > >>>Fixing it to be more efficient in its use of entropy and also fixing the > >>>fact its not actually a good random number source would be worth looking > >>>at however. > >>> > >>Yes, since current behavior on network irq is very pessimistic. > > > >No, it's very optimistic. The network should not be trusted. > > You keep saying that. I am refering to your previous attempts last year to > remove net drivers from sources of entropy. No real changes were done. Dave and I are both a bit stubborn on this point. I've been meaning to respin those patches.. > If the network should not be trusted, then a patch should make sure network > interrupts feed /dev/urandom but not /dev/random at all. (ie not calling > credit_entropy_store() at all) Yes. My plan is to change the interface from SA_SAMPLE_RANDOM to add_network_entropy. The SA_SAMPLE_RANDOM interface sucks because it doesn't tell the core what kind of source it's dealing with. > There is a big difference on get_cycles() and jiffies. You should try to > measure it on a typical x86_64 platform. I'm well aware of that. We'd use get_cycles() exclusively, but it returns zero on lots of platforms. We used to use sched_clock(), I can't remember why that got changed. > >Also, for future reference, patches for /dev/random go through me, not > >through Dave. > > Why ? David is the network maintainer, and he was the one who rejected your > previous patches. Because I'm the /dev/random maintainer and it's considered the polite thing to do, damnit. -- Mathematics is the supreme nostalgia of our time.