[RFC PATCH 4/4] namespace containers: implement enter into existing container

[Serge E. Hallyn]

From: "Serge E. Hallyn" <serue at us.ibm.com>
Subject: [RFC PATCH 4/4] namespace containers: implement enter into existing container

Implement ns container subsys.can_attach().  Remove the constraint
in can_attach() that the destination container must be unpopulated.

When entering a container, if the container's nsproxy has not been
set, set it to the parent container's.  This will eventually support
more complicated creation by composing namespaces from several
nsproxies.

Finally set the task's nsproxy to the container's to effect the
namespace transition.

Signed-off-by: Serge E. Hallyn <serue at us.ibm.com>

---

 kernel/ns_container.c |   30 ++++++++++++++++++++++++++----
 1 files changed, 26 insertions(+), 4 deletions(-)

202011cdde1669d8a7c4f6941ec8c57ea3e19cee
diff --git a/kernel/ns_container.c b/kernel/ns_container.c
index 2d5c578..f13c9ee 100644
--- a/kernel/ns_container.c
+++ b/kernel/ns_container.c
@@ -51,9 +51,6 @@ int ns_can_attach(struct container_subsy
 			return -EPERM;
 	}
 
-	if (atomic_read(&cont->count) != 0)
-		return -EPERM;
-
 	c = task_container(tsk, &ns_subsys);
 	if (c && c != cont->parent)
 		return -EPERM;
@@ -82,6 +79,17 @@ static int ns_create(struct container_su
 	return 0;
 }
 
+/* for now we just take the parnet container nsproxy.
+ * eventually we will construct them based on file link activity */
+static void ns_create_nsproxy(struct nscont *ns, struct container *cont)
+{
+	struct container *parent = cont->parent;
+	struct nscont *parentns;
+	parentns = container_nscont(parent);
+	ns->nsproxy = parentns->nsproxy;
+	get_nsproxy(ns->nsproxy);
+}
+
 /* called from container_clone */
 void ns_set_nsproxy_from_task(struct container *cont, struct task_struct *tsk)
 {
@@ -90,6 +98,20 @@ void ns_set_nsproxy_from_task(struct con
 	get_nsproxy(ns->nsproxy);
 }
 
+void ns_attach(struct container_subsys *ss, struct container *cont,
+		   struct container *old_cont, struct task_struct *tsk)
+{
+	struct nscont *ns = container_nscont(cont);
+	if (!ns->nsproxy) {
+		spin_lock(&ns->lock);
+		if (!ns->nsproxy)
+			ns_create_nsproxy(ns, cont);
+		spin_unlock(&ns->lock);
+	}
+	if (tsk->nsproxy != ns->nsproxy)
+		swap_nsproxies(tsk, ns->nsproxy);
+}
+
 static void ns_destroy(struct container_subsys *ss,
 		       struct container *cont)
 {
@@ -104,7 +126,7 @@ static struct container_subsys ns_subsys
 	.create = ns_create,
 	.destroy  = ns_destroy,
 	.can_attach = ns_can_attach,
-	//.attach = ns_attach,
+	.attach = ns_attach,
 	//.post_attach = ns_post_attach,
 	//.populate = ns_populate,
 	.subsys_id = -1,
-- 
1.1.6