[Qemu-devel] Re: [PATCH v5 4/5] Inter-VM shared memory PCI device

[Avi Kivity <avi@redhat.com>]

On 05/10/2010 07:48 PM, Cam Macdonell wrote:
> On Mon, May 10, 2010 at 10:40 AM, Avi Kivity<avi@redhat.com>  wrote:
>    
>> On 05/10/2010 06:41 PM, Cam Macdonell wrote:
>>      
>>>        
>>>> What would happen to any data written to the BAR before the the handshake
>>>> completed?  I think it would disappear.
>>>>
>>>>          
>>> But, the BAR isn't there until the handshake is completed.  Only after
>>> receiving the shared memory fd does my device call pci_register_bar()
>>> in the callback function.  So there may be a case with BAR2 (the
>>> shared memory BAR) missing during initialization.  FWIW, I haven't
>>> encountered this.
>>>
>>>        
>> Well, that violates PCI.  You can't have a PCI device with no BAR, then have
>> a BAR appear.  It may work since the BAR is registered a lot faster than the
>> BIOS is able to peek at it, but it's a race nevertheless.
>>      
> Agreed.  I'll get Anthony's idea up and running.  It seems that is the
> way forward.
>    

What, with the separate allocation and memcpy?  Or another one?

Why can't we complete initialization before exposing the card and BAR?  
Seems to be the simplest solution.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.