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Re: [Qemu-devel] Proposal for extensions of block job commands in QEMU 1

From: Anthony Liguori
Subject: Re: [Qemu-devel] Proposal for extensions of block job commands in QEMU 1.2
Date: Mon, 21 May 2012 09:19:05 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:11.0) Gecko/20120329 Thunderbird/11.0.1

On 05/21/2012 09:16 AM, Luiz Capitulino wrote:
On Mon, 21 May 2012 09:10:40 -0500
Anthony Liguori<address@hidden>  wrote:

On 05/21/2012 08:59 AM, Luiz Capitulino wrote:
On Fri, 18 May 2012 19:08:42 +0200
Paolo Bonzini<address@hidden>   wrote:

Modified QMP commands

As we have discussed on the ML, we're not going to extend QMP commands.

I understand your reasoning, and since the beginning I thought this was
something useful to do, but we've already settled for not doing this.

I also think that we shouldn't have exceptions, as in practice this means
we're extending commands anyway. So either, we do it or we don't.

Well, I think we should ask ourselves the following question:

How would a client figure out if the new options are available?

This is the primary reason for not extending existing commands.

Yes, I know. But if Paolo implements schema introspection, would you
agree on extending commands.

You seemed to be against even if we had schema introspection.

I'm not against it in principle, just in practice. Today, checking whether a command exists is:

commands = qmp.query_commands()

if 'block-stream' in commands:
    # has block-stream

I have a hard time envisioning how schema introspection can be reasonably implemented in a client.

If we really feel it's important to extend commands, I'd prefer something like per-command capabilities.


Anthony Liguori

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