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

Daniel Veillard veillard at redhat.com
Thu Oct 16 14:59:24 UTC 2008

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

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