From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756036Ab1KHP2V (ORCPT ); Tue, 8 Nov 2011 10:28:21 -0500 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:54403 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751648Ab1KHP2U (ORCPT ); Tue, 8 Nov 2011 10:28:20 -0500 Date: Tue, 8 Nov 2011 10:28:14 -0500 From: Christoph Hellwig To: Pekka Enberg Cc: Christoph Hellwig , Avi Kivity , Alexander Graf , Linus Torvalds , Ingo Molnar , "linux-kernel@vger.kernel.org List" , "kvm@vger.kernel.org list" , qemu-devel Developers , Am?rico Wang , Blue Swirl Subject: Re: [PATCH] KVM: Add wrapper script around QEMU to test kernels Message-ID: <20111108152814.GA8188@infradead.org> References: <1320543320-32728-1-git-send-email-agraf@suse.de> <4EB93FA4.8020800@redhat.com> <20111108145257.GA10846@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 08, 2011 at 05:26:03PM +0200, Pekka Enberg wrote: > On Tue, Nov 8, 2011 at 4:52 PM, Christoph Hellwig wrote: > > Nevermind that running virtfs as a rootfs is a really dumb idea. ?You > > do now want to run a VM that has a rootfs that gets changed all the > > time behind your back. > > It's rootfs binaries that are shared, not configuration. It's > unfortunate but works OK for the single user use case it's meant for. > It's obviously not a proper solution for the generic case. We were > hoping that we could use something like overlayfs to hide the issue > under the rug. Do you think that's also a really dumb thing to do? It doesn't hide your issues. Any kind of unioning will have massive consistency issues (as in will corrupt your fs if you do stupid things) if the underlying layer is allowed to be written to. Thus all the fuzz about making sure the underlying fs can never be mounted writeable in the union mount patches. From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:40012) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RNnb6-0005s6-CO for qemu-devel@nongnu.org; Tue, 08 Nov 2011 10:28:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RNnb4-00014t-SU for qemu-devel@nongnu.org; Tue, 08 Nov 2011 10:28:24 -0500 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:37914 helo=bombadil.infradead.org) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RNnb4-00014K-Q2 for qemu-devel@nongnu.org; Tue, 08 Nov 2011 10:28:22 -0500 Date: Tue, 8 Nov 2011 10:28:14 -0500 From: Christoph Hellwig Message-ID: <20111108152814.GA8188@infradead.org> References: <1320543320-32728-1-git-send-email-agraf@suse.de> <4EB93FA4.8020800@redhat.com> <20111108145257.GA10846@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] [PATCH] KVM: Add wrapper script around QEMU to test kernels List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Pekka Enberg Cc: Blue Swirl , "kvm@vger.kernel.org list" , qemu-devel Developers , "linux-kernel@vger.kernel.org List" , Alexander Graf , Christoph Hellwig , Avi Kivity , Am?rico Wang , Ingo Molnar , Linus Torvalds On Tue, Nov 08, 2011 at 05:26:03PM +0200, Pekka Enberg wrote: > On Tue, Nov 8, 2011 at 4:52 PM, Christoph Hellwig wrote: > > Nevermind that running virtfs as a rootfs is a really dumb idea. ?You > > do now want to run a VM that has a rootfs that gets changed all the > > time behind your back. > > It's rootfs binaries that are shared, not configuration. It's > unfortunate but works OK for the single user use case it's meant for. > It's obviously not a proper solution for the generic case. We were > hoping that we could use something like overlayfs to hide the issue > under the rug. Do you think that's also a really dumb thing to do? It doesn't hide your issues. Any kind of unioning will have massive consistency issues (as in will corrupt your fs if you do stupid things) if the underlying layer is allowed to be written to. Thus all the fuzz about making sure the underlying fs can never be mounted writeable in the union mount patches.