[Qemu-devel] Re: [RFC] New API for asynchronous monitor commands

[Anthony Liguori <anthony@codemonkey.ws>]

On 01/22/2010 01:03 PM, Adam Litke wrote:
> Qemu has a number of commands that can operate asynchronously (savevm, migrate,
> etc) and it will be getting more.  For these commands, the user monitor needs
> to be suspended, but QMP monitors could continue to to accept other commands.
> This patch introduces a new command API that isolates the details of handling
> different monitor types from the actual command execution.
>
> A monitor command can use this API by implementing the mhandler.cmd_async
> handler (or info_async if appropriate).  This function is responsible for
> submitting the command and does not return any data although it may raise
> errors.  When the command completes, the QMPCompletion callback should be
> invoked with its opaque data and the command result.
>
> The process for submitting and completing an asynchronous command is different
> for QMP and user monitors.  A user monitor must be suspended at submit time and
> resumed at completion time.  The user_print() function must be passed to the
> QMPCompletion callback so the result can be displayed properly.  QMP monitors
> are simpler.  No submit time setup is required.  When the command completes,
> monitor_protocol_emitter() writes the result in JSON format.
>
> This API can also be used to implement synchronous commands.  In this case, the
> cmd_async handler should immediately call the QMPCompletion callback.  It is my
> hope that this new interface will work for all commands, leading to a
> drastically simplified monitor.c once all commands are ported.
>
> Thanks to Anthony for helping me out with the initial design.
>
> Signed-off-by: Adam Litke<agl@us.ibm.com>
> To: Anthony Liguori<anthony@codemonkey.ws>
> cc: Luiz Capitulino<lcapitulino@redhat.com>
> Cc: qemu-devel@nongnu.org
>    

I like this a lot and I'd like to see us remove cmd_new in place of 
cmd_async. The conversion is pretty easy since we just have to add a 
cb(ret_data) to the end of synchronous functions.

Luiz/Markus/Avi, what do ya'll think?

Regards,

Anthony Liguori