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

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

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 also provides a mechanism to change the default 
properties between machine types/versions which is ideal as we can 
introduce a kvm-specific machine type where we enable some of these 
things by default.

-- 
Regards,

Anthony Liguori