Re: [libvirt] [Qemu-devel] Re: Libvirt debug API

Richard W.M. Jones wrote: > On Fri, Apr 09, 2010 at 10:06:51PM +0100, Jamie Lokier wrote: > > Daniel P. Berrange wrote: > > > I think this alteration of existing args is faaaar too complex & fragile, > > > and way overkill. > > > > Would it not be simpler, for the target audience, for the config to > > contain a one-line shell script to transform particular matched > > arguments in any way that's wanted? > > I might be missing something but I thought you could already do this > in current libvirt. ie. Change the <emulator> element [1] to point to > your shell script: > > <emulator>/usr/local/bin/my-qemu-wrapper.sh</emulator> > > The wrapper should get called with the command line arguments and you > can alter them however you like. > > Isn't that right, Dan? That forces the shell script to be relatively complicated and recognise all qemu arguments (including version specific ones) to skip the ones with parameters - and to know where to look for the real target executable is. It's not a very friendly way to add or change parts of specific subsystems, for example modifying a blockdev parameter, but it can be done that way if necessary. It's not that hard to write this for trivial extra options: <emulator>/bin/sh -c 'qemu "$0" "$@" -extra-flag'</emulator> (if that works).

Parsing libvirt output and having to guess which option corresponds to what from the libvirt config sounds very fragile and also a rather large amount of effort for something which should be easy.

And then there's modifying how network tap devices are set up and other networking, outside qemu, but requested by libvirt. Doing that in <emulator> sounds like a bad idea, but script hooks are the only sane way to make networking fit every environment and requirement. Ideally without forcing the hook writer to reimplement the normal network setup from scratch just to tweak it a bit. I apologise if libvirt already provides such hooks - I haven't looked at that part of it.