Re: [RFC PATCH 18/18] hw/core/qdev: Display warning for devices missing migration state

[Philippe Mathieu-Daudé]

On 7/9/20 9:14 PM, Peter Maydell wrote:
> On Fri, 3 Jul 2020 at 21:19, Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>>
>> When built with --enable-qdev-debug, QEMU displays warnings
>> listing devices missing migration state:
>>
>>   $ qemu-system-arm -S -M spitz
>>   qemu-system-arm: warning: missing migration state for type: 
>> 'pxa270-c0-arm-cpu'
>>   qemu-system-arm: warning: missing migration state for type: 'serial'
>>   qemu-system-arm: warning: missing migration state for type: 'pxa2xx-pcmcia'
>>   qemu-system-arm: warning: missing migration state for type: 'pxa2xx-pcmcia'
>>   qemu-system-arm: warning: missing migration state for type: 
>> 'pxa2xx-i2c-slave'
>>   qemu-system-arm: warning: missing migration state for type: 
>> 'pxa2xx-i2c-slave'
>>   qemu-system-arm: warning: missing migration state for type: 'ads7846'
>>   qemu-system-arm: warning: missing migration state for type: 'max1111'
>>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>> RFC because there might be something simpler than --enable-qdev-debug.
> 
> I think where we'd like to get to is installing a migration
> blocker if the machine has any devices which don't have a vmsd.
> But for that we'd need to be pretty sure we'd got all the devices
> on machines where we care about migration, and we're clearly a
> fair way from that (eg we need to do something about the
> devices like the CPU which don't have a vmsd but handle their
> migration some other way so they don't trigger the condition
> for warning/migration-blocker).

Dave made a comment about it, I'd rather let him have a look.

> I don't have a strong objection to this --enable-qdev-debug, I guess.
> Another option halfway between this and a full migration-blocker
> would be do a warn_report() for the relevant devices when savevm
> tries to migrate them.

OK. The problem is vmstate_save_state() is not qdev specific, it
migrates a blob, which we can not report much about. I'll repost
using 2 warnings.

Thanks for your review,

Phil.