Re: [Qemu-devel] [RFC] Plan for moving forward with QOM

[Anthony Liguori]

On 09/15/2011 01:31 AM, Gleb Natapov wrote:
> On Wed, Sep 14, 2011 at 01:04:00PM -0500, Anthony Liguori wrote:
> > All device relationships are identified as named properties.  A QOM
> > path name
> > consists of a named device, followed by a series of properties which
> > may or may
> > not refer to other devices.  For instance, all of the following are
> > valid paths:
> >
> >   /i440fx/piix3/i8042/aux
> >   /i440fx/slot[1.0]/i8042/aux
> >   /i440fx/slot[1.0]/bus/piix3/i8042/aux
> Have you looked at device paths generated by get_fw_dev_path() in qdev?
> This function generates Open Firmware device path. The difference
> between OF device path and the examples above is that OF device path has
> a meaning outside of QEMU and can be used by firmware to find a device
> a path refers too. Will QOM be able to generate them?
>
> The paths look like:
> /address@hidden/address@hidden,1/address@hidden/address@hidden
> /address@hidden/address@hidden/address@hidden/address@hidden
> /address@hidden/address@hidden/address@hidden/address@hidden
> /address@hidden/address@hidden,1/address@hidden/address@hidden
> /address@hidden/address@hidden,1/address@hidden/address@hidden
> /address@hidden/address@hidden/address@hidden,0
> /address@hidden/address@hidden/address@hidden
> /address@hidden/address@hidden/address@hidden
> /address@hidden/address@hidden,1/address@hidden/address@hidden
> /address@hidden/address@hidden/address@hidden/address@hidden/address@hidden
> /address@hidden/address@hidden,2/address@hidden/address@hidden
> /address@hidden/address@hidden,2/address@hidden/address@hidden/address@hidden
> /address@hidden/linuxboot.bin
>
> For isa machines:
> /isa/address@hidden/address@hidden/address@hidden
> /isa/address@hidden/address@hidden
> /isa/address@hidden/address@hidden
> /isa/address@hidden/address@hidden/address@hidden

A critical point that I neglected to previously mention is that while qdev has a 
canonical path (only one path, really) to address a device, QOM does not.  That 
means a different approach is needed to make the graph look like a tree as OF 
requires.

You need something like this:

void generate_tree(Device *node)
{
   if (IS_PCI_BUS(node)) {
      for (i = 0; i < 32; i++) {
         generate_tree(lookup_device(get_property(node, "slot[%d]", i)));
      }
   } else if (IS_ISA_BUS(node)) {
      ....
   } else {
      // leaf node, generate path segment
   }
}

There are certainly ways to walk the graph generically (by coloring or following 
the composition paths) but that won't give you the desired ordering.

Regards,

Anthony Liguori
}

> --
>                         Gleb.