c/r: introduce CHECKPOINT_RESTORE symbol

For checkpoint/restore we need auxilary features being compiled into the
kernel, such as additional prctl codes, /proc/<pid>/map_files and etc...
but same time these features are not mandatory for a regular kernel so
CHECKPOINT_RESTORE config symbol should bring a way to disable them all at
once if one wish to get rid of additional functionality.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Andrew Vagin <avagin@openvz.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Vasiliy Kulikov <segoon@openwall.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/Kconfig

@@ -783,6 +783,17 @@ config DEBUG_BLK_CGROUP
 
 endif # CGROUPS
 
+config CHECKPOINT_RESTORE
+	bool "Checkpoint/restore support" if EXPERT
+	default n
+	help
+	  Enables additional kernel features in a sake of checkpoint/restore.
+	  In particular it adds auxiliary prctl codes to setup process text,
+	  data and heap segment sizes, and a few additional /proc filesystem
+	  entries.
+
+	  If unsure, say N here.
+
 menuconfig NAMESPACES
 	bool "Namespaces support" if EXPERT
 	default !EXPERT