Re: [libvirt] [PATCH 09/10] libxl: Stubdom emulator type

On Thu, Feb 19, 2015 at 10:19:22PM +0100, Marek Marczykowski-Górecki wrote: > On Thu, Feb 19, 2015 at 01:45:52PM -0700, Jim Fehlig wrote: > > Marek Marczykowski-Górecki wrote: > > > Xen have feature of having device model in separate domain (called stub > > > domain). Add a 'type' attribute to 'emulator' element to allow selecting > > > such a configuration. > > > > Or maybe 'mode', describing the mode in which the emulator runs: as a > > process or as a VM. > > > > > Emulator path is still used for qemu running in dom0 (if > > > any). Libxl currently do not allow to select stubdomain path. > > > > > > > That seems to overload a single <emulator>. Would it be better to have > > multiple <emulators>? E.g. > > > > <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator> > > <emulator mode='stubdomain'>/usr/lib/xen/bin/stubdom-dm</emulator> > > So the existence of <emulator mode='stubdomain'/> would enable this feature? > What if someday the default will be to run stubdomain emulator - how > the user can disable it in such case? This suggests to me we need to have two separate controls. First an attribute / element somewhere saying what device mode is used, and the second (optionally) saying what the path to the stubdom emulator is. eg no stubdomain: <devices> <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator> ... </devices> Stubdomain with default path <devices> <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator> <stubdomain enabled="yes|no"/> </devices> Stubdomain with custom path <devices> <emulator>/usr/lib/xen/bin/qemu-system-i386</emulator> <stubdomain enabled="yes|no"> <emulator>/usr/lib/xen/bin/stubdom-dm</emulator> </stubdomain> </devices>

We can of course not worry about this 3rd option until libxl actually supports this. So, just implement <stubdomain enabled="yes|no"/> for now. If <stubdomain> is not listed in the XML from the application, the XML post-parse callback can be used by the hypervisor to fill in the default either <stubdomain enabled="yes"/> or <stubdomain enabled="no"/> as appropriate. So that copes with xen changing its default in the future