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

[Jan Kiszka]

Jan Kiszka wrote:
> 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 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.
>>
> 
> Hmm, the refactoring of the old command line switches to -rtc is, if I
> understand qdev and -set correctly, widely orthogonal. Or is the policy
> now to freeze all command line switches in favor of the -device and
> -set?. However, I will look into qdev conversion of the PC RTC.

Thinking further: Is there a way to discover the available qdev device
parameters via the command line?

Jan

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