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 ? Daniel -- Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/ daniel@veillard.com | Rpmfind RPM search engine http://rpmfind.net/ http://veillard.com/ | virtualization library http://libvirt.org/