From: Mark Brown Subject: Re: [PATCH] random: add blocking facility to urandom Date: Mon, 12 Sep 2011 18:06:57 +0100 Message-ID: <20110912170657.GA10452@sirena.org.uk> References: <1314974248-1511-1-git-send-email-jarod@redhat.com> <1315417137-12093-1-git-send-email-jarod@redhat.com> <1315419179.3576.6.camel@lappy> <4E67B75B.8010500@redhat.com> <20110907192737.GD20571@thunk.org> <4E6E1103.2000408@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ted Ts'o , Sasha Levin , linux-crypto@vger.kernel.org, Matt Mackall , Neil Horman , Herbert Xu , Steve Grubb , Stephan Mueller , lkml To: Jarod Wilson Return-path: Received: from cassiel.sirena.org.uk ([80.68.93.111]:40989 "EHLO cassiel.sirena.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751206Ab1ILRHH (ORCPT ); Mon, 12 Sep 2011 13:07:07 -0400 Content-Disposition: inline In-Reply-To: <4E6E1103.2000408@redhat.com> Sender: linux-crypto-owner@vger.kernel.org List-ID: On Mon, Sep 12, 2011 at 10:02:43AM -0400, Jarod Wilson wrote: > Ted Ts'o wrote: > >Yeah, but there are userspace programs that depend on urandom not > >blocking... so your proposed change would break them. > I'm already consigned to the fact this isn't going to fly, but I'm > still curious to know examples of programs that are going to break > here, for my own education. Its already possible for urandom reads > to fail as the code is now (-ERESTARTSYS and -EFAULT are possible), > so a sane program ought to already be handling error cases, though > not -EAGAIN, which this would add. It's not just a question of error handling existing, it's also about the expectations the system has for the behaviour of the file - if urandom is expected to always be able to return data an application is likely to rely on the fact that it's effectively non-blocking anyway and not bother setting non-blocking mode at all and so have no graceful handling for this.