pidns: add the struct bsd_acct_struct pointer on pid_namespace struct

All the bsdacct-related info will be stored in the area, pointer by this
one.

It will be NULL automatically for all new namespaces.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/pid_namespace.h

@@ -14,6 +14,8 @@ struct pidmap {
 
 #define PIDMAP_ENTRIES         ((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
 
+struct bsd_acct_struct;
+
 struct pid_namespace {
 	struct kref kref;
 	struct pidmap pidmap[PIDMAP_ENTRIES];
@@ -25,6 +27,9 @@ struct pid_namespace {
 #ifdef CONFIG_PROC_FS
 	struct vfsmount *proc_mnt;
 #endif
+#ifdef CONFIG_BSD_PROCESS_ACCT
+	struct bsd_acct_struct *bacct;
+#endif
 };
 
 extern struct pid_namespace init_pid_ns;