From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752009AbZHHPZN (ORCPT ); Sat, 8 Aug 2009 11:25:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751873AbZHHPZM (ORCPT ); Sat, 8 Aug 2009 11:25:12 -0400 Received: from atrey.karlin.mff.cuni.cz ([195.113.26.193]:42749 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751678AbZHHPZL (ORCPT ); Sat, 8 Aug 2009 11:25:11 -0400 Date: Fri, 7 Aug 2009 20:08:42 +0200 From: Pavel Machek To: Zachary Amsden Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, axboe@kernel.dk, hch@infradead.org, akpm@linux-foundation.org, Paul.Clements@steeleye.com, tytso@mit.edu Subject: Re: [PATCH] Allow userspace block device implementation Message-ID: <20090807180841.GC1728@ucw.cz> References: <4A6D79F6.3050509@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A6D79F6.3050509@redhat.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi! > Well, it may be a good, bad, idiotic or brilliant idea depending on your > personal philosophy. I went down this route out of pragmatism. > Hopefully I have not fully re-invented the wheel. I did, long ago. I called it nbd... aha and you know about it (from following mails in thread). > accidental deadlock. There may of course be some hidden deep deadlock > potential in such a device, especially if one decided to use it as a > swap device, but again, this is a philosophical issue. What's philosophical about 'it does not work for swap or dirty mmap'? (last time I checked, dirty mmap data behaved very much like swap). (And yes, nbd has same problem. It should be safe for r/o access to localhost, but may deadlock when it is mounted locally...) And yes, I believe that's show stopper. OTOH if you _can_ solve that... then you have some rather significant advantage over nbd. (But guaranteeing progress for dirty writeout will be tricky even with mlocked userland, AFAICT...) -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html