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

[Avi Kivity]

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.

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