Re: [Qemu-devel] [PATCH][RESEND] Add monitor command for system_reboot

[Anthony Liguori <aliguori@us.ibm.com>]

Ryan Harper wrote:
>> It's a different class of non-determinism though.  With 
>> system_powerdown, you make a request to the guest.  You don't know 
>> whether the guest will comply with the request.  The same level of 
>> non-determinism exists with ballooning.
>>
>> With system_reboot, you're taking an action (system_reset) and what's 
>> not deterministic is whether you're taking that action based on what 
>> someone requested on the monitor (system_reboot) verses whether you're 
>> taking that action based on something the user did (shutdown).  In the 
>> later case, you're action is functionally incorrect.
>>     
>
> Only if the shutdown from the user occurs in timeout period.  So, yes,
> it's still present, but the window of the behavior can be much
> smaller.
>
> I still think this is a reasonable approach even with that window.
>   

It's still a policy decision and the question is whether QEMU is the 
right place to implement that policy.  QEMU provides a mechanism today 
to implement this policy (system_powerdown followed by polling via info 
status followed by system_reset).

I tend to agree with Avi that we don't want to implement these sort of 
policies in QEMU and that we instead want to take a PV approach that can 
let us eliminate the nastier non-determinism.

-- 
Regards,

Anthony Liguori