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

[Avi Kivity]

On 05/10/2010 07:48 PM, Cam Macdonell wrote:
> On Mon, May 10, 2010 at 10:40 AM, Avi Kivity<address@hidden>  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.