Namespaces compatibility list
  
  This document contains the information about the problems user
  may have when creating tasks living in different namespaces.
  
  Here's the summary. This matrix shows the known problems, that
  occur when tasks share some namespace (the columns) while living
  in different other namespaces (the rows):
  
  	UTS	IPC	VFS	PID	User	Net
  UTS	 X
  IPC		 X	 1
  VFS			 X
  PID		 1	 1	 X
  User		 2	 2		 X
  Net						 X
  
  1. Both the IPC and the PID namespaces provide IDs to address
     object inside the kernel. E.g. semaphore with IPCID or
     process group with pid.
  
     In both cases, tasks shouldn't try exposing this ID to some
     other task living in a different namespace via a shared filesystem
     or IPC shmem/message. The fact is that this ID is only valid
     within the namespace it was obtained in and may refer to some
     other object in another namespace.
  
  2. Intentionally, two equal user IDs in different user namespaces
     should not be equal from the VFS point of view. In other
     words, user 10 in one user namespace shouldn't have the same
     access permissions to files, belonging to user 10 in another
     namespace.
  
     The same is true for the IPC namespaces being shared - two users
     from different user namespaces should not access the same IPC objects
     even having equal UIDs.
  
     But currently this is not so.