Re: [libvirt] [Xen-devel] [PATCH] libxl: allow an <emulator> to be selected in the domain config XML

Hi, [added xen-devel: FYI this is about how to properly set the libxl device_model_version when the user has provided a manual device_model override (aka a path to a qemu) in the libvirt domain XML.] On 30/04/13 16:10, Jim Fehlig wrote: > David Scott wrote: >> The emulator path supplied can be any valid path on the system. >> >> Note that when setting a device_model, libxl needs us to set the >> device_model_version too. The device_model_version can be either >> >> ...QEMU_XEN: meaning "upstream qemu", the default in xen-4.3 onwards >> ...QEMU_XEN_TRADITIONAL: the old xen-specific fork >> >> We detect the device_model_version by examining the qemu filename: >> if it is "qemu-dm" then it's the old xen-specific fork. If anything >> else then we assume "upstream qemu" (whose filename may change >> in future). Note that if you are using a wrapper script to (eg) >> adjust the arguments of the old qemu during development, you will >> have to ensure the wrapper script also has the name "qemu-dm", by >> placing it in a separate directory. >> > > That is unfortunate. Users could have existing config with > <emulator>/usr/bin/my-qemu-dm</emulator> which works with the legacy > stack but not with libxl right? Is it possible to safely query the > binary to determine if it is qemu-dm? From my reading of libxl, it doesn't seem to have any way to detect the type of a given qemu binary (or at least I couldn't spot it). I think that if we were to write some detection code we should probably add it to libxl rather than libvirt -- what do you think?

The other options I can think of are: 1. weaken the test so we interpret any filename containing the substring "qemu-dm" as traditional-- this would catch your case at least

2. flip the default around so that if an <emulator> is provided we assume traditional unless the filename is "qemu-system-i386" (or maybe just "contains qemu-system-i386" or "contains qemu-system")

3. add libxl driver-specific XML (is that possible?) to allow the user to override a libvirt default. It would be a shame to expose the complexity to the libvirt client though.