[PATCH] pidns: Place under CONFIG_EXPERIMENTAL (take 2)

[ebiederm@xmission.com (Eric W. Biederman)]

This is my trivial patch to swat innumerable little bugs
with a single blow.

After some intensive review (my apologies for not having
gotten to this sooner) what we have looks like a good
base to build on with the current pid namespace code but
it is not complete, and it is still much to simple to find
issues where the kernel does the wrong thing outside of
the initial pid namespace.

Until the dust settles and we are certain we have the ABI and
the implementation is as correct as humanly possible let's keep
process ID namespaces behind CONFIG_EXPERIMENTAL. 

Allowing us the option of fixing any ABI or other bugs
we find as long as they are minor.

Allowing users of the kernel to avoid those bugs simply
by ensuring their kernel does not have support for multiple
pid namespaces.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 include/linux/pid_namespace.h |   22 ++++++++++++++++++++++
 init/Kconfig                  |   12 ++++++++++++
 kernel/pid.c                  |    2 ++
 3 files changed, 36 insertions(+), 0 deletions(-)

diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 0135c76..0227e68 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 +46,27 @@ 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 8b88d0b..72e37c0 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 d1db36b..f815455 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)
 {
-- 
1.5.3.rc6.17.g1911