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. Berrangé 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. > > > > > > 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. > > > > You must /sometimes/ supply the correct machine type. > > > > 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 > > > > 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. > > All I'm suggesting here is just adding extra hints that OpenStack > can use. > > 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. > > 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=scsi \ --property hw_vif_model=e1000e Or if they're using libosinfo to set preferred devices openstack image set \ --property os_distro=fedora26 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=q35 --property os_distro=fedora26 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. > > > > 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. > > There's nothing preventing OVF from supporting the same kind of > hints. > > 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. > > 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 > > > > > > Thoughts? > > > > I tend to think we'd be better looking at what we can do in the context > > of an existing standard like OVF rather than inventing something that > > only works with qcow2. I think it would need to be more expressive than > > just a single list of key,value pairs for each item. > > 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. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|