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Date: Tue, 14 Jul 2009 10:06:07 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: Re: [Qemu-devel] [PATCH] monitor: Add port write command
References: <4A5C3FBB.10306@siemens.com>
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, qemu-devel <qemu-devel@nongnu.org>

Jan Kiszka wrote:
> Useful for testing hardware emulations or manipulating its state to
> stress guest drivers.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>   

Patch looks good.

Makes me think of an idea I had a while ago.  It's a rather radical 
change but I think we could target it for 0.12.  Today, the vast 
majority of our save/restore code looks like:

save:
// version checks
qemu_put_type(f, &field);
...

load:
// version checks
qemu_get_type(f, &field);
...
// optional depending on version
qemu_get_type(f, &field);

device_reset(s);

We could convert this to something this to be largely data drive.  For 
instance,

SaveVMFields fields[] = {
 { offsetof(DeviceState, field), "field", TYPE, VERSION },
 {},
};

SaveVMDescription desc = {
  .fields = fields,
  .version = CURRENT_VERSION,
  .reset = device_reset,
};

What would be really cool about this change is that we could introduce a 
new set of commands to manipulate device state.  We could save/restore 
individual device state and that would allow us to dump device state via 
the monitor and to manipulate individual fields of the device state.  I 
think this could be pretty useful for debugging.

I'm curious if anyone else is interested in this sort of change.

Regards,

Anthony Liguori