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Re: [Qemu-devel] [RFC] QEMU Dbus support - a proposal management API

From: Anthony Liguori
Subject: Re: [Qemu-devel] [RFC] QEMU Dbus support - a proposal management API
Date: Tue, 11 Dec 2007 09:48:22 -0600
User-agent: Thunderbird (X11/20071022)

Richard W.M. Jones wrote:
Anthony Liguori wrote:
Daniel P. Berrange wrote:
Or have 2 monitor interaction modes. One mode uses the command line style suitable for people / scripting languages. The other umode ses a binary XDR
protocol for serializing the args & returns values for formal control
APIs to use in a easy manner. It ought to be reasonably straightforward to
add a binary serialization format for all existing commands

I don't think binary is inherently easier to parse than text provided that some thought is put into the format of the textual output.

XDR (aka RFC 1014 & RFC 4506) does let you generate complex interfaces with relative ease. For example, here's the description of the remote protocol used by libvirt:


"Parsing" is done for you by stubs that are generated from the above file.

On the downside it turns out that it's not very well supported under Windows. For libvirt I had to basically port an XDR implementation by hand to MinGW and add extra functions from glibc to it.

I think we just want to levels of verbosity.

This would work too.

On the point of controlling multiple qemu instances on a machine from a single place: Easiest way to do this would be to direct all the monitor sockets into a single known directory. Something along the lines of:

  qemu -monitor unix:/var/lib/qemu-monitors/`uuidgen`,nowait

A control process can then just keep an eye on entries under that directory, and (unlike libvirtd) it's robust against the control process restarting.

Actually, this was the original intention of the -name parameter. What a management tool would want to do is:

1) if -name is specified by user, generate one with uuidgen
2) pass -name <name> and -pidfile /path/to/well/known/location/name.pid

This will ensure uniqueness of name without requiring the creation tool to maintain any state (so no daemon is required). Right now, you would also have to store a monitor socket in that well known path. However, I'm working on a VNC tunnels patch right now that would allow the monitor to be tunneled through a VNC session. The idea here is that a management tool could just store a hint about the VNC location and then you can get at the rest of the character devices through the VNC session.

Otherwise, you end up with a bunch of temporary sockets for things like the monitor, serial devices, parallel devices, etc.


Anthony Liguori


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