[CRIU] support for dumping containers with an external master mount

[Tycho Andersen]

Hi all,

Here's a patch that allows c/r of containers who have external sharing. I tried
today to write a test for it (you can see a draft at [1]), but I couldn't get
it working successfully. After I pivot_root in the test, criu fails to dump:

(00.002741) Error (files-reg.c:821): Unable to look up the 19 mount
(00.002755) Error (cr-dump.c:1616): Dump files (pid: 5912) failed with -1
(00.002988) Error (cr-dump.c:1979): Dumping FAILED.

Mount id 19 is /dev in this case; so I suppose I have to re-create most of the
fs inside the pivot_root in order to c/r? Is there an easier way to test this?

I've tested this with LXC and it seems to restore things ok:
http://paste.ubuntu.com/10726229/

Thoughts are appreciated.

Tycho

[1]: https://github.com/tych0/criu/commit/351adbe2ea01b70600e6a131a8e064b57a188ba2