Re: [Qemu-devel] [PATCH 3/3 v2] Add a pc-0-10 machine type for compatibility with 0.10.x

[Gerd Hoffmann <kraxel@redhat.com>]

On 07/08/09 23:45, Anthony Liguori wrote:
> Gerd Hoffmann wrote:
>> On 07/08/09 17:08, Mark McLoughlin wrote:
>>> On Wed, 2009-07-08 at 16:09 +0200, Gerd Hoffmann wrote:
>>>>> /usr/share/qemu/configs/pc-0-10.dts
>>>>> /usr/share/qemu/configs/pc-0-11.dts
>>>>> /usr/share/qemu/configs/pc -> /usr/share/qemu/configs/pc-0-11.dts
>>>> Doesn't work. Your virtio blk device isn't in there.
>>>
>>> Right - I had assumed Anthony meant that such a config file would also
>>> have details on the defaults used for devices which can be added to that
>>> machine.
>>
>> Could probably be done that way, but that wouldn't be different from a
>> global compat variable where the virtio-block-pci driver looks at.
>> We have different versions of devices.
>
> We have options that we can tweak for devices. That doesn't mean they're
> versioned. What the default set of options that is turned on for any
> given device is determined by the machine type (since the machine init
> is what creates the devices to start with).

The machine init doesn't create all devices.  USB devices are created 
outside machine init today, and that will become more and more common.

I expect long-term we will end up with one of these two models:

   (1) - machine init creates just the bare devices, i.e. what is there
         when you specify just '-M pc'.  Either hardcoded or from
         machine config file.
       - generic code adds devices added by cmd line switches.

   (2) - command line switches insert additional devices into the bare
         (-M pc) device tree.
       - The virtual machine is created from that modified device tree.

I both cases it is not clear how the machine init / machine config will 
handle the versioning of the devices added by command line switches.

We could have each machine type register a list of default options. 
Using qdev properties that should be doable in a fairly generic way, 
like this:

virtio-blk-pci and virtio-console-pci get a "class" property. 
virtio-net-pci gets a "msi" property.  ide-disk+cdrom gets a 
"fw-version" property (well, not yet, when being converted to qdev).

pc-0.10 could then register a list of default properties, i.e. something 
like

   "virtio-blk-pci"     => "class=0x??"
   "virtio-console-pci" => "class=0x??"
   "virtio-net-pci      => "msi=0"
   "ide-disk"           => "fw-version=0.10.0"

When creating devices qdev would apply them.

I can prototype that.

comments?

   Gerd