Re: [Qemu-devel] Re: [PATCH 0/22] Refactor machine support

[Anthony Liguori <anthony@codemonkey.ws>]

On 06/09/2010 03:47 PM, Blue Swirl wrote:
> On Wed, Jun 9, 2010 at 2:30 PM, Paul Brook<paul@codesourcery.com>  wrote:
>    
>>>>> Because at some point the base tree will have to be written in C.
>>>>>            
>>>> No. You can start with a completely empty machine.
>>>> We don't/shouldn't need any machine specific C code.
>>>>          
>>> I think you're missing the argument.  I should be possible to create a
>>> machine entirely from a FDT or via -device options.
>>>
>>> However, to continue to support the interfaces that we support today, it
>>> will be necessary to have C code that manipulates a base device tree.
>>>
>>> When a user specifies '-M pc -hda foo.img'  verses '-M versatilepb -hda
>>> foo.img', the equivalent are two very different operations on a device
>>> tree.  The former adds an ide disk to the default controller and the
>>> later potentially creates a new scsi bus and then adds a disk to a
>>> specific bus.
>>>        
>> AFAICS the current commandline options only result in simple addition of
>> devices. They might add slightly different devices in slightly different
>> places, but that's easy to accommodate by having the machine define a few
>> standard device/bus IDs.
>>
>> IMO it's even more lame if -hda shops working when you supply a device tree.
>>      
> The tree supplied by the user should label a bus node with a property
> 'QEMU,hda'. The C version (called by the board) would be something
> like setprop("/i440fx/pci.0/ide.0", "QEMU,hda"). QEMU should search
> the device tree for such labels at startup.
>    

That works for the very simple case of -hda, but what do you do for:

-drive file=foo.img,bus=0,index=2

I think it's possible to come up with some form of solution once you 
start adding synthetic properties or dummy devices but ultimately I 
think it pollutes the device tree.  I think the easiest way to support 
the interfaces we provide now is to just code the device tree 
manipulation in C.

Regards,

Anthony Liguori