From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Daniel P. Berrange" Subject: Re: RFC: Making QEMU honour 'readonly' flag for disks Date: Thu, 31 Jul 2008 12:45:11 +0100 Message-ID: <20080731114511.GA18548@redhat.com> References: <20080724113627.GU1138@redhat.com> <18568.34189.57005.491667@mariner.uk.xensource.com> <18576.11753.2777.902201@mariner.uk.xensource.com> <20080730091608.GI30193@redhat.com> Reply-To: "Daniel P. Berrange" Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20080730091608.GI30193@redhat.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Ian Jackson Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Wed, Jul 30, 2008 at 10:16:08AM +0100, Daniel P. Berrange wrote: > On Wed, Jul 30, 2008 at 10:01:29AM +0100, Ian Jackson wrote: > > Daniel P. Berrange writes ("[Xen-devel] RFC: Making QEMU honour 'readonly' flag for disks"): > > > The Xen disk configuration syntax allows a block device to be marked as > > > readonly, exclusive writable or shared writeable. The xen hotplug scripts > > > will clash for clashing configs between domains, but it is upto the > > > backend drivers to actually enforce the readonly flag on I/O operations. > > > The paravirt backend disk driver does this fine, but QEMU's emulated > > > backend driver does not. > > > > I still think this is a fix we should have but your patch is very > > intrusive. Is there some reason why you didn't just invent > > BDRV_O_RDONLY_NO__ACTUALLY__READONLY ? A new parameter to bdrv_new > > seems quite wrong. > > > > (It's a shame that the existing BDRV_O_RDONLY does something strange > > and probably wrong, but we probably don't want to fix that in our > > branch.) > > Yeah, I'm actually attempting to fix that craziness, which is why > I've not posted an update yet. I think it may actually be easier > to fix that it appears.... Take a look at my patch on qemu-devel subject of "PATCH: Control over drive open modes for backing file" If that gets into QEMU, the xen specific bit will merely involve changing the xenstore.c file to pass correct flags to bdrv_open() instead of using the default '0'. Regards, Daniel -- |: Red Hat, Engineering, London -o- http://people.redhat.com/berrange/ :| |: http://libvirt.org -o- http://virt-manager.org -o- http://ovirt.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: GnuPG: 7D3B9505 -o- F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|