Re: [Qemu-devel] Re: Machine-readable or parseable qemu output

[Anthony Liguori <anthony@codemonkey.ws>]

Daniel P. Berrange wrote:
> On Wed, Jan 14, 2009 at 11:29:38AM +0000, Richard W.M. Jones wrote:
>   
>> On Wed, Jan 14, 2009 at 04:40:05PM +0530, Amit Shah wrote:
>>     
>>> - Have a libqemumonitor.so that will abstract out output from qemu and
>>>   provide a machine-readble output for the consumer
>>>       
>> Why do we need a C API at all?  IMHO it'd be better just to make the
>> existing qemu monitor output more machine-friendly, meaning consistent
>> delimiters so that programs can reliably resynchronize with the
>> output, and consistent guarantees on error messages.
>>     
>
> Well if we have async messages over a separate channel, we can already
> reliably resynchronize with the output, because QEMU will eventually
> produce its '(qemu) ' prompt on a new line. So if something goes wrong
> you just need to skip until you find the prompt again.  Changing QEMU
> monitor prompt will just break all existing libvirt deployments, and
> any other programs relying on currently prompt.
>
> IMHO, any libqemumonitor.so should be made to work with current monitor
> format as its starting point, and then extend from there, not change
> any existing characteristics. This provides forwards & backwards compat
> for all apps, albeit at cost of slightly more complex internals for
> the libqemumonitor.so - but this complexity will be centralized in one
> place instead of all apps using QEMU, so this is still a net win.
>   

The monitor today is *not* meant to be parsed.  I know people do it, but 
it's not intended to.  I don't want to introduce all the nutty 
complexity into QEMU to pretend like it's been a supported interface 
since 0.8.0.  Let's make it a supported, stable interface and move forward.

Regards,

Anthony Liguori

> Daniel
>