Re: [libvirt] PATCH: Experimental User Mode Linux driver for libvirt

On Thu, Oct 16, 2008 at 12:42:17PM +0100, Daniel P. Berrange wrote: [...] > Like QEMU, UML has an admin monitor console. It is a little different > though, using a UNIX domain socket, in datagram mode, sending command > strings back & forth. This actaully makes it a little easier to deal > with in libvirt. User mode linux has a uml_mconsole command line tool > to interact with it, but I directly implement the socket support in > libvirt instead, so this driver does not (yet) have any dependancy on > the UML utilities. > > The driver is largely a clone of the QEMU driver, replacing the bit which > builds the command line argv, and all code dealing with the QEMU monitor. > Since the monitor socket is datagram based, we can't make use of it for > detecting VM shutdown as we do with QEMU/LXC. So instead, I make use of > inotify, to monitor $HOME/.uml which is populated witha directory for > each VM. When we see a directory created, libvirt marks the corresponding > VM as running, finds it PID & probes the monitor for the PTY config. When > we see a directory deleted, libvirt makes the VM as shutoff and frees any > resources its holding. This actually works very nicely & simply. Seems then that this driver could be made restarteable easilly in case of libvirtd shutdown/restart, right ? Since everything is available from the filesystem and there is no tight coupling between libvirtd and the uml process, it even seems a starting libvirtd would be able to discover and manage uml instances which were not started with libvirt, right ?