[PATCH RFC 05/25] net: Add primitives to update heads of pernet_list sublists

[Kirill Tkhai]

Currently we have first_device, and device and subsys
sublists. Next patches introduce one more sublist.
So, move the functionality, which will be repeating,
to the primitives.

Signed-off-by: Kirill Tkhai <ktk...@virtuozzo.com>
---
 net/core/net_namespace.c |   19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index a8ea580885d9..1d9712973695 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -939,6 +939,18 @@ static void __unregister_pernet_operations(struct 
pernet_operations *ops)
 
 static DEFINE_IDA(net_generic_ids);
 
+#define update_first_on_add(first, delim, added)       \
+       do {                                            \
+               if (first == delim)                     \
+                       first = added;                  \
+       } while (0)
+
+#define update_first_on_del(first, to_delete)          \
+       do {                                            \
+               if (first == to_delete)                 \
+                       first = (to_delete)->next;      \
+       } while (0)
+
 static int register_pernet_operations(struct list_head *list,
                                      struct pernet_operations *ops)
 {
@@ -1045,8 +1057,8 @@ int register_pernet_device(struct pernet_operations *ops)
        int error;
        down_write(&net_sem);
        error = register_pernet_operations(&pernet_list, ops);
-       if (!error && (first_device == &pernet_list))
-               first_device = &ops->list;
+       if (!error)
+               update_first_on_add(first_device, &pernet_list, &ops->list);
        up_write(&net_sem);
        return error;
 }
@@ -1064,8 +1076,7 @@ EXPORT_SYMBOL_GPL(register_pernet_device);
 void unregister_pernet_device(struct pernet_operations *ops)
 {
        down_write(&net_sem);
-       if (&ops->list == first_device)
-               first_device = first_device->next;
+       update_first_on_del(first_device, &ops->list);
        unregister_pernet_operations(ops);
        up_write(&net_sem);
 }