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Re: [libvirt] [PATCH] Workaround for broken kernel autofs mounts



On 11/01/2011 07:00 AM, Daniel P. Berrange wrote:
From: "Daniel P. Berrange"<berrange redhat com>

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
wierd error message like

s/wierd/weird/


   Failed to unmount '/.oldroot/sys/kernel/security':Too many levels of symbolic links

Atttempting to detach the autofs mount mount using umount2(MNT_DETACH)

s/Atttempting/Attempting/
s/mount mount/mount/

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.

Agree to that analysis.

ACK.

--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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