3 files changed, 37 insertions, 0 deletions

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 0135c76c76c6..1689e28483e4 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -29,6 +29,7 @@ struct pid_namespace {
 
 extern struct pid_namespace init_pid_ns;
 
+#ifdef CONFIG_PID_NS
 static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
 {
         if (ns != &init_pid_ns)
@@ -45,6 +46,28 @@ static inline void put_pid_ns(struct pid_namespace *ns)
                 kref_put(&ns->kref, free_pid_ns);
 }
 
+#else /* !CONFIG_PID_NS */
+#include <linux/err.h>
+
+static inline struct pid_namespace *get_pid_ns(struct pid_namespace *ns)
+{
+        return ns;
+}
+
+static inline struct pid_namespace *
+copy_pid_ns(unsigned long flags, struct pid_namespace *ns)
+{
+        if (flags & CLONE_NEWPID)
+                ns = ERR_PTR(-EINVAL);
+        return ns;
+}
+
+static inline void put_pid_ns(struct pid_namespace *ns)
+{
+}
+
+#endif /* CONFIG_PID_NS */
+
 static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk)
 {
         return tsk->nsproxy->pid_ns;
diff --git a/init/Kconfig b/init/Kconfig
index 5b92e3aa1366..c5b354b1409e 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -215,6 +215,18 @@ config USER_NS
           vservers, to use user namespaces to provide different
           user info for different servers.  If unsure, say N.
 
+config PID_NS
+        bool "PID Namespaces (EXPERIMENTAL)"
+        default n
+        depends on EXPERIMENTAL
+        help
+          Suport process id namespaces.  This allows having multiple
+          process with the same pid as long as they are in different
+          pid namespaces.  This is a building block of containers.
+
+          Unless you want to work with an experimental feature
+          say N here.
+
 config AUDIT
         bool "Auditing support"
         depends on NET
diff --git a/kernel/pid.c b/kernel/pid.c
index d1db36b94674..f815455431bf 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -537,6 +537,7 @@ err_alloc:
         return NULL;
 }
 
+#ifdef CONFIG_PID_NS
 static struct pid_namespace *create_pid_namespace(int level)
 {
         struct pid_namespace *ns;
@@ -621,6 +622,7 @@ void free_pid_ns(struct kref *kref)
         if (parent != NULL)
                 put_pid_ns(parent);
 }
+#endif /* CONFIG_PID_NS */
 
 void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 {