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). But for things like modifications to particular devices, wouldn't it be better to associate "add cache=special option" to a section about one of the blockdevs which libvirt knows about, rather than the awful prospect of parsing libvirt's output to guess which of three -device arguments corresponds with the second SCSI drive mentioned in the libvirt config - which might not necessarily be the second on the command line, even.