Re: [Qemu-devel] Re: [PATCH 08/11] QMP: Port balloon command

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

Luiz Capitulino wrote:
> On Tue, 23 Jun 2009 08:59:42 -0500
> Anthony Liguori <anthony@codemonkey.ws> wrote:
>
>   
>> How this gets output can then be conditional on control mode vs. human 
>> mode.  In human mode, we can use human-friendly units like MBs.  In 
>> control mode, we would always use bytes.
>>     
>
>  For me, this is one of the hardest aspects of the project.
>
>  It is more general than unit conversion, the problem is: how should
> commands output (specially multline) look like?
>
>  I have talked with Eduardo about this, and I have chosen the simplest
> approach, which is prefixing commands output by '='. That is, the
> protocol doesn't change commands output, just adds prefixes.
>   

I'm not saying you should change command output.  Most commands follow a 
similar format quite intentionally.  That's:

<header>: <param>=<value>[,<param>=<value>[...]]

I'm just suggesting that you codify that instead of leaving it open 
coded everywhere.  Nothing more than that.

>  This approach has the advantage of making the protocol merge very
> easy and I believe it will be less painful to maintain as well.
>   

FWIW, you could introduce monitor_printf_list() as your first patch.

>>> We also need a way to discover that the command is available:
>>>       
>> I think we want to version each command too.
>>     
>
>  making it quite complicated. :)
>
>  If we go this way (of defining an output for each command or even
> defining a version for each command) I fear we will take forever
> to get in agreement and merge the whole series.
>
>  Another related question is: should we port 100% of the command
> set up front or can we merge small sets, defining a new version of
> the protocol each time?
>
>  What I would like to do for QMP V1 is:
>
> 1. Keep what this series is doing, that is, keep commands output
> unchanged and only add prefixes (unit conversion is ok though)
>
> 2. Define a set of commands to be part of V1, and port them
>
>  We can try to port the whole set as fast as we can (say, until
> V3). Right after that, we could start improving commands output.
>   

I wanted to respond to the top level, but here's what I see as the 
potential merge plan:

1) Make all commands return a value
2) Add a mechanism to mark commands as being "structured"
3) Get the structured printfs in order.
4) Merge

I won't want QMP to be exposed as a usable interface until all commands 
are converted.  This means holding off on the last patch I think.  I 
don't think we'll get QMP for 0.11.  I think it's likely going to be a 
0.12 feature.  However, I'd like to start merging this series as soon as 
humanly possible.  I think it's already pretty close.

-- 
Regards,

Anthony Liguori