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

[Anthony Liguori <anthony@codemonkey.ws>]

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:
> /pci@i0cf8/ide@1,1/drive@1/disk@0
> /pci@i0cf8/isa@1/fdc@03f1/floppy@1
> /pci@i0cf8/isa@1/fdc@03f1/floppy@0
> /pci@i0cf8/ide@1,1/drive@1/disk@1
> /pci@i0cf8/ide@1,1/drive@0/disk@0
> /pci@i0cf8/scsi@3/disk@0,0
> /pci@i0cf8/ethernet@4/ethernet-phy@0
> /pci@i0cf8/ethernet@5/ethernet-phy@0
> /pci@i0cf8/ide@1,1/drive@0/disk@1
> /pci@i0cf8/isa@1/ide@01e8/drive@0/disk@0
> /pci@i0cf8/usb@1,2/network@0/ethernet@0
> /pci@i0cf8/usb@1,2/hub@1/network@0/ethernet@0
> /rom@genroms/linuxboot.bin
>
> For isa machines:
> /isa/ide@0170/drive@0/disk@0
> /isa/fdc@03f1/floppy@1
> /isa/fdc@03f1/floppy@0
> /isa/ide@0170/drive@0/disk@1

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.
>