Re: [Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_iterate()

[Thomas Huth <thuth@redhat.com>]

On 09.11.2016 16:13, Dr. David Alan Gilbert wrote:
> * Thomas Huth (thuth@redhat.com) wrote:
>> On 09.11.2016 08:18, Amit Shah wrote:
>>> On (Fri) 04 Nov 2016 [14:10:17], Thomas Huth wrote:
>>>> qemu_savevm_state_iterate() expects the iterators to return 1
>>>> when they are done, and 0 if there is still something left to do.
>>>> However, ram_save_iterate() does not obey this rule and returns
>>>> the number of saved pages instead. This causes a fatal hang with
>>>> ppc64 guests when you run QEMU like this (also works with TCG):
>>>
>>> "works with" -- does that mean reproduces with?
>>
>> Yes, that's what I've meant: You can reproduce it with TCG (e.g. running
>> on a x86 system), too, there's no need for a real POWER machine with KVM
>> here.
> 
> How did you trigger it on x86?

As described below - qemu-img + qemu-system-ppc64 + savevm is enough to
trigger it on a x86 host.

> 
>>>>  qemu-img create -f qcow2  /tmp/test.qcow2 1M
>>>>  qemu-system-ppc64 -nographic -nodefaults -m 256 \
>>>>                    -hda /tmp/test.qcow2 -serial mon:stdio
>>>>
>>>> ... then switch to the monitor by pressing CTRL-a c and try to
>>>> save a snapshot with "savevm test1" for example.

 Thomas