[Qemu-devel] Re: Live migration broken when under heavy IO

[Avi Kivity]

On 06/16/2009 03:57 PM, Anthony Liguori wrote:
> > > The tricky bit is that this has to happen at the device layer 
> > > because the opaques cannot be saved in a meaningful way.
> >
> > Do you mean the device has to record all cancelled requests and 
> > replay them?  I think we can do it at the block layer (though we have 
> > to avoid it for nested requests).
>
> In order to complete the requests, you have to call a callback and 
> pass an opaque with the results.  The callback/opaque cannot be saved 
> in the block layer in a meaningful way.

You're right, of course.  I guess we'll have to cancel any near term 
cancellation plans.

We could change the opaque to be something pre-registered (e.g. the 
device state object, which we don't need to save/restore) and pass in 
addition an integer request tag.  These would be migratable.  The device 
would be responsible for saving tags and their associated information 
(perhaps through a common API).

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