From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50749) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fKrGH-0001bo-22 for qemu-devel@nongnu.org; Mon, 21 May 2018 16:18:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fKrGF-0006sM-Kv for qemu-devel@nongnu.org; Mon, 21 May 2018 16:18:29 -0400 Date: Mon, 21 May 2018 21:18:17 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20180521201817.GA10382@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20180518180440-mutt-send-email-mst@kernel.org> <20180518170956.GI8615@redhat.com> <20180518174133.GC25013@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180518174133.GC25013@localhost.localdomain> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] storing machine data in qcow images? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: "Michael S. Tsirkin" , stefanha@redhat.com, kwolf@redhat.com, mreitz@redhat.com, qemu-devel@nongnu.org, qemu-block@nongnu.org On Fri, May 18, 2018 at 02:41:33PM -0300, Eduardo Habkost wrote: > On Fri, May 18, 2018 at 06:09:56PM +0100, Daniel P. Berrang=C3=A9 wrote= : > > On Fri, May 18, 2018 at 06:30:38PM +0300, Michael S. Tsirkin wrote: > > > Hi! > > > Right now, QEMU supports multiple machine types within > > > a given architecture. This was the case for many architectures > > > (like ARM) for a while, somewhat more recently this is the case > > > for x86 with I440FX and Q35 options. > > >=20 > > > Unfortunately this means that it's no longer possible > > > to more or less reliably boot a VM just given a disk image, > > > even if you select the correct QEMU binary: > > > you must supply the correct machine type. > >=20 > > You must /sometimes/ supply the correct machine type. > >=20 > > It is quite dependent on the guest OS you have installed, and even > > just how the guest OS is configured. In general Linux is very > > flexible and can adapt to a wide range of hardware, automatically > > detecting things as needed. It is possible for a sysadmin to build > > a Linux image in a way that would only work with I440FX, but I > > don't think it would be common to see that. Many distros build > > and distribute disk images that can work across VMWare, KVM, > > and VirtualBox which all have very quite different hardware. > > Non-x86 archs may be more fussy but I don't have personal > > experiance with them > >=20 > > Windows is probably where things get more tricky, as it is not > > happy with disks moving between different controller types > > for example, and you might trigger license activation again. >=20 > All I'm suggesting here is just adding extra hints that OpenStack > can use. >=20 > I have very specific goal here: the goal is to make it less > painful to users when OpenStack+libvirt+QEMU switch to using a > different machine-type by default (q35), and/or when guest OSes > stop supporting pc-i440fx. I assume this is a goal for OpenStack > as well. >=20 > We can make the solution to be more extensible and solve other > problems as well, but my original goal is the one above. Configuring the machine type is just one thing that users would do with OpenStack though. A simple example might be openstack image set \ --property hw_disk_bus=3Dscsi \ --property hw_vif_model=3De1000e Or if they're using libosinfo to set preferred devices=20 openstack image set \ --property os_distro=3Dfedora26 which will identify virtio-blk & virtio-net as disk+nic respectively. Using libosinfo is more flexible than setting the hw_disk_bus & hw_vif_model explicitly, because libosinfo will report multiple devices that can be used, and the virt driver can then pick one which best suits the particular host or hypervisor. Setting a non-default machine type is one extra prop openstack image set \ --property hw_machine_type=3Dq35 --property os_distro=3Dfedora26 So while your immediate motivation is only considering the machine type, from the Openstack POV thats only one property out of many that users might be setting. > > That said I'm not really convinced that using the qcow2 headers is > > a good plan. We have many disk image formats in common use, qcow2 > > is just one. Even if the user provides the image in qcow2 format, > > that doesn't mean that mgmt apps actually store the qcow2 file. > >=20 >=20 > Why this OpenStack implementation detail matters? Once the hints > are included in the input, it's up to OpenStack to choose how to > deal with it. Well openstack aims to support multiple hypervisors - if there's a choice between implementing something that is a cross-vendor standard like OVF, or implementing something that only works with qcow2, the latter is not very appealing to support. > > The closest to a cross-hypervisor standard is OVF which can store > > metadata about required hardware for a VM. I'm pretty sure it does > > not have the concept of machine types, but maybe it has a way for > > people to define metadata extensions. Since it is just XML at the > > end of the day, even if there was nothing official in OVF, it would > > be possible to just define a custom XML namespace and declare a > > schema for that to follow. >=20 > There's nothing preventing OVF from supporting the same kind of > hints. >=20 > I just don't think we should require people to migrate to OVF if > all they need is to tell OpenStack what's the recommended > machine-type for a guest image. >=20 > Requiring a different image format seems very likely to not > fulfill the goal I stated above: it will require using different > tools to create the guest images, and we can't force everybody > publishing guest images to stop using qcow2. It doesn't have to require different tools - existing tools could create a OVF/OVA file for the disk image as part of an "export" process. > > > - We most likely shouldn't get backend parameters from the image > > >=20 > > > Thoughts? > >=20 > > I tend to think we'd be better looking at what we can do in the conte= xt > > of an existing standard like OVF rather than inventing something that > > only works with qcow2. I think it would need to be more expressive th= an > > just a single list of key,value pairs for each item. >=20 > Why you claim we are inventing something that only works with > qcow2? It works with a disk image format that has ability to record extra metadata. With raw files you would have to have a separate file to record it, likewise for any other vendor disk formats that are not extended.=20 Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|