Re: [Qemu-devel] [Patch] [kinda-resend] persistent real-time-clock

[Anthony Liguori <anthony@codemonkey.ws>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>>>
>>> I'm not sure I understood what you suggest here.
>>>
>>> Plainly storing the rtc state on file is not enough, as unlike with 
>>> real
>>> hardware, nothing will advance it when the power is off.
>>>   
>>
>> If you made the CMOS non-volatile, what you would store in the CMOS 
>> is the clock-offset, not the actual clock time.  Then when the VM 
>> started up again, it would Just Work.
>>
>> You would probably have to use a different location in CMOS to store 
>> the offset than what the guest relies on to read the current time.
>
> Under this, the CMOS would not be read by the guest at any time.  So 
> why store the CMOS at all?  Store the offset somewhere and avoid the 
> CMOS (gaining the ability to work on targets without nonvolatile memory).
>
> It's config file territory, not CMOS.

It's a bios parameter (just like default boot device).  It makes sense 
to allow the bios to let the user customize bios parameters and have 
that be saved.

CMOS is non-volatile in real life so making it non-volatile in QEMU 
seems like the obvious thing to do.

Regards,

Anthony Liguori