Re: [Qemu-devel] [PATCHv2 1/8] Introduce deriver_name field to DeviceInfo structure.

[Gleb Natapov <gleb@redhat.com>]

On Sat, Nov 06, 2010 at 10:01:25AM +0100, Markus Armbruster wrote:
[skip]
> > Why should Seabios match against three (or even more) different type of
> > devices to detect ata interface? Why require Seabios changes when this
> > can be avoided (if new device that provide ata is added)? OpenBIOS also
> > supports qemu BTW (this is Open Firmware implementation for pc, you can
> > run and see what kind of device paths it generates). 
> 
> I think we've finally cut through the confusion caused by the
> unfortunate choice of driver_name for this new device attribute.
> 
> The fact that you choose values of your driver_name in a way that is
> inspired by the syntactic conventions of IEEE 1275 is not its
> distinguishing characteristic.  The values of existing member name are
> inspired by that as well.  driver_name's distinguishing characteristic
> is its purpose: communication with SeaBIOS.
> 
My understanding of this name in IEEE 1275 is that it specifies what
driver in FW handles a device.

> I'm fine with you choosing its values however it's convenient for that
> purpose, as long as you give it a name reflecting that purpose.  What
> about fw_name and qdev_fw_name()?
> 
I am not attached to the name. Can "alias" be used for that purpose?

> 
> Next, I'm worried about overloading of method get_dev_path().  It's
> being used for a very specific purpose: savevm/loadvm.  
> 
This part of the patch is not completed yet. I intend to change the code
in savevm/loadvm to call qdev_get_dev_path() to get full device path
there.

> * It's currently defined only for PCI devices.  Your PATCH 7/8 changes
>   its value there, from DOMAIN:BUS:SLOT.FUNCTION to FW_NAME@SLOT.
> 
Old definition is buggy BTW. BUS part is controlled by a guest and may
be different from default value at destination.

>   - The old value identifies the qdev.  The new value does not
>     (remember, we have a separate qdev per PCI function).  Why is this
>     okay?
> 
No no. New value is FW_NAME@SLOT,FUNC. Spec says that if FUNC is zero it
can be omitted.

>   - Is the value saved with the VM?  If yes, this is an incompatible
>     change.
Don't understand that remark.

> 
> * You extend it for ISA and System bus (PATCH 5,6/8).  How does this
>   affect savevm?
> 
We should ask savevm experts. As far as I can see it affects id
creation. As long as id is unique we should be OK. We may send more info
on migration after the patches.

--
			Gleb.