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>

2 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/ipc_namespace.h b/include/linux/ipc_namespace.h
index c3b1da9e5feb..ea6c18a8b0d4 100644
--- a/include/linux/ipc_namespace.h
+++ b/include/linux/ipc_namespace.h
@@ -52,6 +52,7 @@ extern atomic_t nr_ipc_ns;
 #define INIT_IPC_NS(ns)         .ns             = &init_ipc_ns,
 
 extern int register_ipcns_notifier(struct ipc_namespace *);
+extern int cond_register_ipcns_notifier(struct ipc_namespace *);
 extern int unregister_ipcns_notifier(struct ipc_namespace *);
 extern int ipcns_notify(unsigned long);
 
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index 20dfed590183..0ff6224d172a 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -121,6 +121,10 @@ extern int raw_notifier_chain_register(struct raw_notifier_head *nh,
 extern int srcu_notifier_chain_register(struct srcu_notifier_head *nh,
                 struct notifier_block *nb);
 
+extern int blocking_notifier_chain_cond_register(
+                struct blocking_notifier_head *nh,
+                struct notifier_block *nb);
+
 extern int atomic_notifier_chain_unregister(struct atomic_notifier_head *nh,
                 struct notifier_block *nb);
 extern int blocking_notifier_chain_unregister(struct blocking_notifier_head *nh,