Prevent internal tmpfs mount to override files in /tmp

Runsc wants to mount /tmp using internal tmpfs implementation for
performance. However, it risks hiding files that may exist under
/tmp in case it's present in the container. Now, it only mounts
over /tmp iff:
  - /tmp was not explicitly asked to be mounted
  - /tmp is empty

If any of this is not true, then /tmp maps to the container's
image /tmp.

Note: checkpoint doesn't have sentry FS mounted to check if /tmp
is empty. It simply looks for explicit mounts right now.
PiperOrigin-RevId: 229607856
Change-Id: I10b6dae7ac157ef578efc4dfceb089f3b94cde06

0 files changed, 0 insertions, 0 deletions