[Qemu-devel] Re: [PATCH] monitor: Add port write command

[Anthony Liguori <anthony@codemonkey.ws>]

Juan Quintela wrote:
> We were thinking about that functionality some time ago.  We were
> looking at an apic bug during migration, and it was not trivial to dump
> apic state before and after migration.
>
> I took a look at it, and basically decided that I would have to
> replicate the savevm method.  Your apprearch mean that doing the command
> is trivial, and we have "meaningful" labels for it.
>
> Will take a look at using that in some driver.
>   

Great.  I think an incremental conversion is the right approach.  If we 
tie this into qdev correctly, then we could also do some nice things 
with migration.  We could dump out a file that describes any given 
migration protocol version.  We could then use this to automatically 
check whether we broke the migration format between versions but just 
doing a diff.

I think there's also an opportunity to adjust the migration protocol.  
One change I had to make to the savevm format was removing all of the 
size parameters.  This is because the nature of QEMUFile makes it such 
that you don't know what the size was until you actually wrote data.  
The old savevm format used to rely on seeking to update the size 
parameter.  If we know the size of the section (based on the 
description), we can reintroduce this to the protocol.

What's more, we can probably get rid of QEMUFile all together and 
introduce a more useful abstraction that doesn't have such complex 
buffering.

This refactoring is definitely high on my 0.12 wish list :-)

Regards,

Anthony Liguori