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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] Re: [PATCH v3 2/3] qerror: Add a new MACHINE_STOPPED error message |
Date: | Fri, 27 Aug 2010 14:37:54 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.11) Gecko/20100713 Lightning/1.0b1 Thunderbird/3.0.6 |
On 08/27/2010 02:24 PM, Luiz Capitulino wrote:
I don't see how 0.13.0 is going to get releases with anything but the current behavior. It's unfortunate but we're too delayed and can't afford a change like this this late in the game. In terms of the stable branch, the least disruptive thing would be a timeout.Okay.I think we have agreed on the internal interfaces approach. My only concern is whether this will conflict when extending the wire protocol (eg. adding new arguments to existing commands). Not a problem if the C API is not stable, of course.We don't do that. It's a recipe for disaster. QEMU isn't written in Python and if we try to module our interfaces are if we were a Python library, we're destined to fail.You mean we don't do simple protocol extensions? So, if we need an new argument to an existing command, we add a new command instead? Just because QEMU is not written in Python?
Because it's too easy to get it wrong in QEMU. Here's the rationale.If I can't trivially call a QMP function in C, then I'm not going to use QMP functions within QEMU. I'm not going to create an embedded JSON string just to call a function with three integer arguments.
Yes, if we need to do that, we can create a C API that both the QMP interface uses and we also use internally but why? All that does is introduce the chance that the C API will have more features than the QMP interface.
If we don't use these functions in QEMU, then how do we know that these functions have reasonable semantics? This is exactly the problem we suffer today. We have internal APIs that do reasonable things but everything that deals with QMP is a special case. That creates too many opportunities to get things wrong.
I think it's a vitally important requirement that all future QMP functions have direct mappings to a C interface. The long term goal should be for that interface to be used by all of the command line arguments, SDL, and the human monitor. If those things only relied on a single API and we exposed that API via QMP, than we would have an extremely useful interface.
Regards, Anthony Liguori
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