From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762258AbYDPK1r (ORCPT ); Wed, 16 Apr 2008 06:27:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756960AbYDPK1j (ORCPT ); Wed, 16 Apr 2008 06:27:39 -0400 Received: from yw-out-2122.google.com ([74.125.46.25]:63187 "EHLO yw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755586AbYDPK1j (ORCPT ); Wed, 16 Apr 2008 06:27:39 -0400 MIME-Version: 1.0 Message-ID: Date: Wed, 16 Apr 2008 03:27:26 -0700 (PDT) In-Reply-To: X-IP: 86.53.68.233 References: User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (X11; U; x86_64 Linux; en_GB; rv:1.8.0.4) Gecko/20060508 Firefox/1.5.0.4,gzip(gfe),gzip(gfe) Subject: Re: RFC: Self-snapshotting in Linux From: Alan Jenkins To: Ben Nizette Cc: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ben Nizette wrote: > On Wed, 2008-04-16 at 16:44 +0800, Peter Teoh wrote: > > Essentially, to reiterate the key idea: able to snapshot the current > > kernel+userspace permanent.....restore from another snapshot....and > > then switch back again if needed etc.....will the implementation be > > difficult...if not impossible???? > > > > As I see it the main thing is that VMWare doesn't have to worry about > trying to put hardware in to (and pull out of) low power modes. VMWare > hardware is never left in an undefined state by poorly written drivers > etc. > > I think hibernation is about what you want; snapshotting as you describe > it should fall down for about the same reasons I guess there is the hardware / drivers issue. I would like to claim I've found hibernation to be reliable but unfortunately that's not 100% true. As you say, that's inherent to snapshotting on unvirtualised hardware - calling it snapshotting instead of hibernation wouldn't change anything. I think VMware's real advantages are more about management and convenience. 1) Disk virtualisation. It's much more convenient to create a VMware image than a new linux partition. Linux will let you use disk images on a filesystem using the loopback driver, but that tends not to be well supported by installers. wubi[1] is the obvious counterexample here. 2) Linux hibernation does the in-memory snapshot OK, but the *filesystem* obviouslly isn't a part of that snapshot. In some unfortunate circumstances, you can end up resuming a memory image which is not consistent with the filesystem and corrupting it. IMHO filesystems need to include a "last modified" timestamp and check it on resume. [1] http://wubi-installer.org/