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[Seth Forshee <seth.forshee+lp@xxxxxxxxxxxxx>]

Note that it's also possible to do this without namespaces at all, and
it definitely seems to be force unmount which makes it happen.

$ fuseext2 ext2.img /tmp/d
$ sudo mount --bind /tmp/d mount
$ sudo umount -f mount
$ ls /tmp/d
ls: cannot access /tmp/d: Transport endpoint is not connected

Other filesystems which implement umount_begin such as nfs also seem to
start tearing down their connections in the callback, so I suspect they
might behave similarly in this scenario. I'm going to test with nfs to
verify.

I don't really think that fuse can detect this situation. It seems like
do_umount potentially needs to handle this differently in the case of a
bind mount, but I'm not actually sure whether or not the behavior here
is actually what's expected to happen.

The other question is whether or not lxc acutally needs to use MNT_FORCE
when unmounting. What's the reason for doing so?

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https://bugs.launchpad.net/bugs/1402834

Title:
  fuse filesystems get disconnected on container exit

Status in linux package in Ubuntu:
  Confirmed

Bug description:
  When bind-mounting a directory from a fuse filesytems into a container,
  then when the container is shut down, the userspace process serving the
  fuse fs is terminated.  The original fuse mountpoint remains busy until it
  is manually unmounted.

  I've tested this with sshfs, git://github.com/stgraber/cgmanagerfs,
  the bbfs example fs from http://www.cs.nmsu.edu/~pfeiffer/fuse-tutorial/,
  or git://github.com/lxc/lxcfs.

  To reproduce:

  Mount a fusefs - say sshfs - with -o allow_other, let's say onto
  /tmp/d.

  sshfs -f -d -o allow_other somehost:$HOME /tmp/d

  Bind that into a container by adding

  lxc.mount.entry = /tmp/d freezer none bind,create=dir 0 0

  to the container's config.

  start the container, stop it.

  the fuse program stops (exits 0 in fact)

  the mount is not cleaned up - ls /tmp/d on the host henceforth
  complains:

  	ls: cannot access /tmp/d Transport endpoint is not connected"
  	
  (sudo umount /tmp/d cleans it up)

  I don't know for sure whether this is a kernel or libfuse bug.

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