ipc: re-enable msgmni automatic recomputing msgmni if set to negative

The enhancement as asked for by Yasunori: if msgmni is set to a negative
value, register it back into the ipcns notifier chain.

A new interface has been added to the notification mechanism:
notifier_chain_cond_register() registers a notifier block only if not already
registered.  With that new interface we avoid taking care of the states
changes in procfs.

Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
Cc: Yasunori Goto <y-goto@jp.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: Pierre Peiffer <pierre.peiffer@bull.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c
index c7974609defc..70ff09183f7b 100644
--- a/ipc/ipcns_notifier.c
+++ b/ipc/ipcns_notifier.c
@@ -61,6 +61,15 @@ int register_ipcns_notifier(struct ipc_namespace *ns)
         return blocking_notifier_chain_register(&ipcns_chain, &ns->ipcns_nb);
 }
 
+int cond_register_ipcns_notifier(struct ipc_namespace *ns)
+{
+        memset(&ns->ipcns_nb, 0, sizeof(ns->ipcns_nb));
+        ns->ipcns_nb.notifier_call = ipcns_callback;
+        ns->ipcns_nb.priority = IPCNS_CALLBACK_PRI;
+        return blocking_notifier_chain_cond_register(&ipcns_chain,
+                                                        &ns->ipcns_nb);
+}
+
 int unregister_ipcns_notifier(struct ipc_namespace *ns)
 {
         return blocking_notifier_chain_unregister(&ipcns_chain,