cgroups: implement namespace tracking subsystem

When a task enters a new namespace via a clone() or unshare(), a new cgroup
is created and the task moves into it.

This version names cgroups which are automatically created using
cgroup_clone() as "node_<pid>" where pid is the pid of the unsharing or
cloned process.  (Thanks Pavel for the idea) This is safe because if the
process unshares again, it will create

	/cgroups/(...)/node_<pid>/node_<pid>

The only possibilities (AFAICT) for a -EEXIST on unshare are

	1. pid wraparound
	2. a process fails an unshare, then tries again.

Case 1 is unlikely enough that I ignore it (at least for now).  In case 2, the
node_<pid> will be empty and can be rmdir'ed to make the subsequent unshare()
succeed.

Changelog:
	Name cloned cgroups as "node_<pid>".

[clg@fr.ibm.com: fix order of cgroup subsystems in init/Kconfig]
Signed-off-by: Serge E. Hallyn <serue@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Cedric Le Goater <clg@fr.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 7 deletions

diff --git a/init/Kconfig b/init/Kconfig
index 6687f805b38d..0007d1b5e867 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -288,6 +288,22 @@ config CGROUP_DEBUG
 
           Say N if unsure
 
+config CGROUP_NS
+        bool "Namespace cgroup subsystem"
+        depends on CGROUPS
+        help
+          Provides a simple namespace cgroup subsystem to
+          provide hierarchical naming of sets of namespaces,
+          for instance virtual servers and checkpoint/restart
+          jobs.
+
+config CGROUP_CPUACCT
+        bool "Simple CPU accounting cgroup subsystem"
+        depends on CGROUPS
+        help
+          Provides a simple Resource Controller for monitoring the
+          total CPU consumed by the tasks in a cgroup
+
 config CPUSETS
         bool "Cpuset support"
         depends on SMP && CGROUPS
@@ -345,13 +361,6 @@ config PROC_PID_CPUSET
         depends on CPUSETS
         default y
 
-config CGROUP_CPUACCT
-        bool "Simple CPU accounting cgroup subsystem"
-        depends on CGROUPS
-        help
-          Provides a simple Resource Controller for monitoring the
-          total CPU consumed by the tasks in a cgroup
-
 config RELAY
         bool "Kernel->user space relay support (formerly relayfs)"
         help