Re: [Qemu-devel] [Question] dump memory when host pci device is used by guest

[Daniel P. Berrange]

On Tue, Oct 18, 2011 at 03:15:29PM +0800, Wen Congyang wrote:
> Hi, Jan Kiszka
> 
> At 10/10/2011 05:34 PM, Jan Kiszka Write:
> > On 2011-10-10 11:02, Daniel P. Berrange wrote:
> >> On Mon, Oct 10, 2011 at 08:52:08AM +0200, Jan Kiszka wrote:
> 
> > 
> > Run gdb with "set debug remote 1" and watch the communication, it is not
> > that complex. But a dump command is probably simpler for those
> > scenarios, I agree.
> 
> I have implemented the command dump and reuse migration's code. But I meet a 
> problem
> when I test it.
> 
> My qemu-kvm's tree is not updated about 2 months ago, because kernel.org is 
> down, and
> I forgot to pull from github.
> 
> After I pull it from github, I find the following changes:
> @@ -1523,9 +1523,7 @@ static void 
> assigned_dev_unregister_msix_mmio(AssignedDevice *dev)
>  
>  static const VMStateDescription vmstate_assigned_device = {
>      .name = "pci-assign",
> -    .fields = (VMStateField []) {
> -        VMSTATE_END_OF_LIST()
> -    }
> +    .unmigratable = 1,
>  };
>  
>  static void reset_assigned_device(DeviceState *dev)
> 
> Why do you remove fields from vmstate_assigned_device?
> It is useful for dump because it does not check unmigratable. If 
> vmstate_assigned_device
> does not contain .fields, qemu will crash in vmstate_save_state().

Given that '.fields' is allowed to be NULL for some devices, I'd say
even for normal migration, QEMU should be checking for NULL in the
vmstate_save_state() code. This would prevent QEMU crashes in the case
where someone removed the .unmigratable member, but forgot to add back
a .fields member.

Daniel
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