On Tue, May 22, 2018 at 05:02:21PM +0200, Kevin Wolf wrote: > Am 22.05.2018 um 16:19 hat Michael S. Tsirkin geschrieben: > > On Tue, May 22, 2018 at 09:35:55AM +0200, Gerd Hoffmann wrote: > > > Hi, > > > > > > > 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. > > > > > > I think it would be pretty hard to actually build such an image. > > > > > > The more critical thing for linux guests is the storage driver which > > > must be included into the initrd so the image can mount the root > > > filesystem. And the firmware, bios vs. uefi is more critical than > > > pc vs. q35. > > > > I think we can start by finding a location to embed a string in a qcow > > image, add ability for qemu-img to set and get this string. We can > > discuss how it's formatted separately. > > If we want it, we'll find a place to store it. > > But the first thing we need is a spec for what's actually in it. Just > storing a machine type hint would be a one-off hack that wouldn't last > very long before we want to add the next thing. > > Essentially, what we need is a description of the virtual machine that > we suggest to use with this image. We can try to reuse something > existing there, like libvirt XML or OVF, or invent something new (a JSON > array describing runtime options?). One difference to existing formats > is probably that we want only frontends and no backends in the > description.
The OVF virtual hardware description might be appropriate to define what's required vs what's recommended, to support multiple machine-types, and ranges of valid values for variables. Pro: management software can reuse exactly the same logic for qcow2 machine descriptions and OVF machine descriptions. Con: OVF is a pretty complex specification. -- Eduardo