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

[Dan Kenigsberg]

On Sun, Apr 27, 2008 at 11:58:17AM -0500, Anthony Liguori wrote:
> Dan Kenigsberg wrote:
>> Real PC lets its user set the real-time-clock and store it on CMOS,
>> which advances the clock even when the PC is offline.
>>
>> These patches will allow doing the same with VM:
>> - Before shutting a VM down, use the monitor's info timeoffset to see
>>   how much (in seconds) does the rtc differ from the host clock.
>> - Store this offset somewhere.
>> - Use it next time with -startdate now+offset.
>>
>> Please tell me what do you think of it.
>>   
>
> I think a more general mechanism that stored nvram in a file would be 
> interesting.  Something like like -nvram file.ram.  This also allows a 
> guest to determine it's initial boot device and for that setting to 
> persist.

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.

Do you suggest to set up a mechanism (in parallel to savevm/loadvm)
where each device with non-volatile memory could register to? Probably,
in most devices the SaveStateHandler could play the role of
SaveNVStateHandler, but some would have to do something else. This would
make the file.ram different than a memory dump.

Regards,

    Dan