Re: [Qemu-devel] Re: [PATCH 0/5] Refactor and enhance RTC configuration

[Gerd Hoffmann <kraxel@redhat.com>]

On 09/09/09 17:40, Anthony Liguori wrote:
> Jan Kiszka wrote:
>> The aim of this series is to allow using the emulated PC RTC (MC146818)
>> as a reliable time source for guests. This is particularly useful if the
>> host runs NTP or has otherwise access to an accurate clock while the
>> guest has not (no network, impossible to add an NTP implementation
>> etc.).
>>
>> To achieve this, the command line switch -rtc is introduced. It takes
>> the option 'clock' to switch between the currently used base ('vm') and
>> the new QEMU_CLOCK_HOST ('host'). At this chance, -rtc is also used to
>> deprecate all the other RTC-related stand-alone switches.
>>
>> First tests indicate that this approach works as expected and could
>> increase the usefulness of the virtual RTC enormously. However, there
>> might be pitfalls I've missed so far. Feedback would be welcome!
>
> You get most of this pretty cheaply with qdev conversion. If you give
> the rtc a default id, you can tweak all of the properties with the -set
> command line option.

It isn't that simple.  -set device.$id.$property=$value works only for 
devices actually created via -device.

cheers,
   Gerd