[Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config breakage

[Anthony Liguori <anthony@codemonkey.ws>]

Michael S. Tsirkin wrote:
> On Tue, Sep 29, 2009 at 09:22:53AM +0200, Avi Kivity wrote:
>   
>> On 09/29/2009 08:58 AM, Michael S. Tsirkin wrote:
>>     
>>> Using bar per feature we'll quickly run out of BARs.
>>> We already use a BAR for MSI-X - let's add
>>> ATA identity there?
>>>    
>>>       
>> Mixing unrelated features will quickly cause confusion.
>>     
>
> Note if we ever switch to 64 bit BARs, we'll only have 3 of these
> available, so the ID would be using the last free one.
> We can just as well plan ahead for when we'll add another feature?
>
> I agree fixed offsets are messy though.  I previously proposed storing
> the offset to the identity data in an i/o register. This will let each
> implementation lay out this data in an optimal manner, without
> confusion.
>   

1) There's no need to make the identity page separate from the config 
space.  The real problem is the config space is too small.  We can fix 
that without making any changes to virtio-blk by putting the config 
space in a separate BAR.

2) Passing an ATA identity page is goofy.  We should just pass the 
serial number and let Linux generate the identity page.  Just because 
Linux requires this as it's user space interface, that doesn't mean that 
other guests will (like Windows).  Instead of exposing an opaque blob, 
we should expose the information we need in a structured way.

Regards,

Anthony Liguori