1=============================
2Namespaces compatibility list
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4
5This document contains the information about the problems user
6may have when creating tasks living in different namespaces.
7
8Here's the summary. This matrix shows the known problems, that
9occur when tasks share some namespace (the columns) while living
10in different other namespaces (the rows):
11
12====	===	===	===	===	====	===
13-	UTS	IPC	VFS	PID	User	Net
14====	===	===	===	===	====	===
15UTS	 X
16IPC		 X	 1
17VFS			 X
18PID		 1	 1	 X
19User		 2	 2		 X
20Net						 X
21====	===	===	===	===	====	===
22
231. Both the IPC and the PID namespaces provide IDs to address
24   object inside the kernel. E.g. semaphore with IPCID or
25   process group with pid.
26
27   In both cases, tasks shouldn't try exposing this ID to some
28   other task living in a different namespace via a shared filesystem
29   or IPC shmem/message. The fact is that this ID is only valid
30   within the namespace it was obtained in and may refer to some
31   other object in another namespace.
32
332. Intentionally, two equal user IDs in different user namespaces
34   should not be equal from the VFS point of view. In other
35   words, user 10 in one user namespace shouldn't have the same
36   access permissions to files, belonging to user 10 in another
37   namespace.
38
39   The same is true for the IPC namespaces being shared - two users
40   from different user namespaces should not access the same IPC objects
41   even having equal UIDs.
42
43   But currently this is not so.
44