[Qemu-devel] Re: RFC qdev path semantics

[Paul Brook]

> > Bus names are chosen by the system as follows:
> > 
> > * If the driver of the parent device model provides a name, use that.
> > 
> > * Else, if the parent device has id ID, use ID.NUM, where NUM is the bus
> > 
> >   number, counting from zero in creation order.
> > 
> > * Else, use TYPE.NUM, where TYPE is derived from the bus type, and NUM
> > 
> >   is the bus number, as above.
> > 
> > ### Paul proposes to drop ID.NUM.
> 
> ABI change: "-device lsi,id=my-scsi -device scsi-disk,bus=my-scsi.0" no
> longer works.

IMO this is a fundamentally broken ABI, so I don't care.
 
> > ### Paul proposes to either drop TYPE.NUM (and require drivers to
> >     provide bus names), or make NUM count separately for each bus type.
> 
> Likewise.

I'd be surprised if anyone actually uses absolute device paths at this time, 
and they're probably going to be broken by other changes.

Using these default bus names as global identifiers is fixable using aliases
(e.g. -device lsi,bus=pci.0).  I'd expect this to cover most interesting uses.
See http://lists.nongnu.org/archive/html/qemu-devel/2010-06/msg02149.html

Paul