On Mon, May 21, 2018 at 09:18:17PM +0100, Daniel P. Berrangé wrote: > 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
Nice. Are these just hypothetical examples, or something that already works? > > 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. Agreed. > > > 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. I still don't understand why you claim this would only work with qcow2. If somebody wants to implement the same functionality in OVF, it's also possible. > > > 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. Requiring a new "export" step that wasn't required before is requiring a different tool, isn't it? > > > > - 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. So this could work with both qcow2 and OVF (and maybe other formats if others want to extend them), wouldn't it? -- Eduardo