[PATCH RFC 06/25] net: Add pernet sys and registration functions

[Kirill Tkhai <ktkhai@virtuozzo.com>]

This is a new sublist of pernet_list, which will live ahead
of already existing:

sys, subsys, device.

It's aimed for subsystems, which pernet_operations may execute
in parallel with any other's pernet_operations. In further,
step-by-step we will move all subsys there, adding necessary
small synchronization locks, where it's need. After all subsys
are moved to sys, we'll kill subsys list and we'll have
all current subsys not requiring net_mutex and to be able
to init and exit in parallel with others.

Then we'll add dev sublist ahead of device, and will repeat
the cycle.

Suggested-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 include/net/net_namespace.h |    2 +
 net/core/net_namespace.c    |   75 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 75 insertions(+), 2 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 10f99dafd5ac..2cde5f766ec6 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -324,6 +324,8 @@ struct pernet_operations {
  * device which caused kernel oops, and panics during network
  * namespace cleanup.   So please don't get this wrong.
  */
+int register_pernet_sys(struct pernet_operations *);
+void unregister_pernet_sys(struct pernet_operations *);
 int register_pernet_subsys(struct pernet_operations *);
 void unregister_pernet_subsys(struct pernet_operations *);
 int register_pernet_device(struct pernet_operations *);
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 1d9712973695..f4f4aaa5ce1f 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -24,10 +24,24 @@
 #include <net/netns/generic.h>
 
 /*
- *	Our network namespace constructor/destructor lists
+ * Our network namespace constructor/destructor lists
+ * one by one linked in pernet_list. They are (in order
+ * of linking): sys, subsys, device.
+ *
+ * The methods from sys for a network namespace may be
+ * called in parallel with any method from any list
+ * for another net namespace.
+ *
+ * The methods from subsys and device can't be called
+ * in parallel with a method from subsys or device.
+ *
+ * When all subsys pernet_operations are moved to sys
+ * sublist, we'll kill subsys sublist, and create dev
+ * ahead of device sublist, and repeat the cycle.
  */
 
 static LIST_HEAD(pernet_list);
+static struct list_head *first_subsys = &pernet_list;
 static struct list_head *first_device = &pernet_list;
 DEFINE_MUTEX(net_mutex);
 
@@ -987,6 +1001,57 @@ static void unregister_pernet_operations(struct pernet_operations *ops)
 		ida_remove(&net_generic_ids, *ops->id);
 }
 
+/**
+ *      register_pernet_sys - register a network namespace system
+ *	@ops:  pernet operations structure for the system
+ *
+ *	Register a subsystem which has init and exit functions
+ *	that are called when network namespaces are created and
+ *	destroyed respectively.
+ *
+ *	When registered all network namespace init functions are
+ *	called for every existing network namespace.  Allowing kernel
+ *	modules to have a race free view of the set of network namespaces.
+ *
+ *	When a new network namespace is created all of the init
+ *	methods are called in the order in which they were registered.
+ *
+ *	When a network namespace is destroyed all of the exit methods
+ *	are called in the reverse of the order with which they were
+ *	registered.
+ */
+int register_pernet_sys(struct pernet_operations *ops)
+{
+	int error;
+	down_write(&net_sem);
+	if (first_subsys != first_device) {
+		panic("Pernet %ps registered out of order.\n"
+		      "There is already %ps.\n", ops,
+		      list_entry(first_subsys, struct pernet_operations, list));
+	}
+	error =  register_pernet_operations(first_subsys, ops);
+	up_write(&net_sem);
+	return error;
+}
+EXPORT_SYMBOL_GPL(register_pernet_sys);
+
+/**
+ *      unregister_pernet_sys - unregister a network namespace system
+ *	@ops: pernet operations structure to manipulate
+ *
+ *	Remove the pernet operations structure from the list to be
+ *	used when network namespaces are created or destroyed.  In
+ *	addition run the exit method for all existing network
+ *	namespaces.
+ */
+void unregister_pernet_sys(struct pernet_operations *ops)
+{
+	down_write(&net_sem);
+	unregister_pernet_operations(ops);
+	up_write(&net_sem);
+}
+EXPORT_SYMBOL_GPL(unregister_pernet_sys);
+
 /**
  *      register_pernet_subsys - register a network namespace subsystem
  *	@ops:  pernet operations structure for the subsystem
@@ -1011,6 +1076,8 @@ int register_pernet_subsys(struct pernet_operations *ops)
 	int error;
 	down_write(&net_sem);
 	error =  register_pernet_operations(first_device, ops);
+	if (!error)
+		update_first_on_add(first_subsys, first_device, &ops->list);
 	up_write(&net_sem);
 	return error;
 }
@@ -1028,6 +1095,7 @@ EXPORT_SYMBOL_GPL(register_pernet_subsys);
 void unregister_pernet_subsys(struct pernet_operations *ops)
 {
 	down_write(&net_sem);
+	update_first_on_del(first_subsys, &ops->list);
 	unregister_pernet_operations(ops);
 	up_write(&net_sem);
 }
@@ -1057,8 +1125,10 @@ int register_pernet_device(struct pernet_operations *ops)
 	int error;
 	down_write(&net_sem);
 	error = register_pernet_operations(&pernet_list, ops);
-	if (!error)
+	if (!error) {
+		update_first_on_add(first_subsys, &pernet_list, &ops->list);
 		update_first_on_add(first_device, &pernet_list, &ops->list);
+	}
 	up_write(&net_sem);
 	return error;
 }
@@ -1076,6 +1146,7 @@ EXPORT_SYMBOL_GPL(register_pernet_device);
 void unregister_pernet_device(struct pernet_operations *ops)
 {
 	down_write(&net_sem);
+	update_first_on_del(first_subsys, &ops->list);
 	update_first_on_del(first_device, &ops->list);
 	unregister_pernet_operations(ops);
 	up_write(&net_sem);