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The kernel automounter is mostly broken wrt to containers. Most notably if you start a new filesystem namespace and then attempt to unmount any autofs filesystem, it will typically fail with a weird error message like Failed to unmount '/.oldroot/sys/kernel/security':Too many levels of symbolic links Attempting to detach the autofs mount using umount2(MNT_DETACH) will also fail with the same error. Therefore if we get any error on unmount()ing a filesystem from the old root FS when starting a container, we must immediately break out and detach the entire old root filesystem (ignoring any mounts below it). This has the effect of making the old root filesystem inaccessible to anything inside the container, but at the cost that the mounts live on in the kernel until the container exits. Given that SystemD uses autofs by default, we need LXC to be robust this scenario and thus this tradeoff is worthwhile. * src/lxc/lxc_container.c: Detach root filesystem if any umount operation fails.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>