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

[Jan Kiszka]

On 2011-10-18 09:58, Daniel P. Berrange wrote:
> 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.

That crash wouldn't be bad because removinb unmigratable without adding
proper fields is almost always a bug.

Jan

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