Re: [Qemu-devel] Re: [PATCH] qemu: make virtio-blk PCI compliant by default

[Anthony Liguori <anthony@codemonkey.ws>]

john cooper wrote:
> Avi Kivity wrote:
>   
>> On 09/22/2009 05:21 PM, john cooper wrote:
>>     
>>>> Can we just read this page as a virtqueue command instead of having it
>>>> mapped permanently?
>>>>      
>>>>         
>>> Probably although I hadn't looked specifically
>>> at doing so.   Mapping the data via an unused
>>> pci bar is pretty trivial and seemed minimally
>>> intrusive to the existing driver.
>>>    
>>>       
>> We'll run out of bars if we expend them like that.
>>     
>
> Agreed.  However my motivation here was to use a
> single additional bar specifically to compensate
> for the PCI spec imposed 256 byte size limitation
> of the config space mapping.  As we're defining the
> content/size of this area, future use to accommodate
> additional data should be unrestricted.
>   

Why expose the whole ATAPI page instead of just the serial number?

I think the proper solution is to move the config to a separate bar 
that's MMIO instead of PIO.  config access is never performance 
sensitive and an MMIO bar has less restrictions on size.

Regards,

Anthony Liguori