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Re: [Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_
Re: [Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_iterate()
Tue, 8 Nov 2016 07:57:52 +0100
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On 08.11.2016 02:14, David Gibson wrote:
> On Fri, Nov 04, 2016 at 02:10:17PM +0100, 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):
>> 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.
>> After the first iteration, ram_save_iterate() always returns 0 here,
>> so that qemu_savevm_state_iterate() hangs in an endless loop and you
>> can only "kill -9" the QEMU process.
>> Fix it by using proper return values in ram_save_iterate().
>> Signed-off-by: Thomas Huth <address@hidden>
> Hmm. I think the change is technically correct, but I'm uneasy with
> this approach to the solution. The whole reason this wasn't caught
> earlier is that almost nothing looks at the return value. Without
> changing that I think it's very likely someone will mess this up
> I think it would be preferable to change the return type to void to
> make it explicit that this function is not directly returning the
> "completion" status, but instead that's calculated from the other
> progress variables it updates.
Not sure how such a patch should finally look like. Could you propose a
Anyway, we're in soft freeze already ... do we still want such a major
change of the logic at this point in time? If not, we should maybe go
with fixing the return type only for 2.8, and do the major change for
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Re: [Qemu-devel] [PATCH for-2.8] migration: Fix return code of ram_save_iterate(), Juan Quintela, 2016/11/14