ipc: recompute msgmni on memory add / remove

Introduce the registration of a callback routine that recomputes msg_ctlmni
upon memory add / remove.

A single notifier block is registered in the hotplug memory chain for all the
ipc namespaces.

Since the ipc namespaces are not linked together, they have their own
notification chain: one notifier_block is defined per ipc namespace.

Each time an ipc namespace is created (removed) it registers (unregisters) its
notifier block in (from) the ipcns chain.  The callback routine registered in
the memory chain invokes the ipcns notifier chain with the IPCNS_LOWMEM event.
 Each callback routine registered in the ipcns namespace, in turn, recomputes
msgmni for the owning namespace.

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, 71 insertions, 0 deletions

diff --git a/ipc/ipcns_notifier.c b/ipc/ipcns_notifier.c
new file mode 100644
index 0000000..0786af6
--- /dev/null
+++ b/ipc/ipcns_notifier.c
@@ -0,0 +1,71 @@
+/*
+ * linux/ipc/ipcns_notifier.c
+ * Copyright (C) 2007 BULL SA. Nadia Derbey
+ *
+ * Notification mechanism for ipc namespaces:
+ * The callback routine registered in the memory chain invokes the ipcns
+ * notifier chain with the IPCNS_MEMCHANGED event.
+ * Each callback routine registered in the ipcns namespace recomputes msgmni
+ * for the owning namespace.
+ */
+
+#include <linux/msg.h>
+#include <linux/rcupdate.h>
+#include <linux/notifier.h>
+#include <linux/nsproxy.h>
+#include <linux/ipc_namespace.h>
+
+#include "util.h"
+
+
+
+static BLOCKING_NOTIFIER_HEAD(ipcns_chain);
+
+
+static int ipcns_callback(struct notifier_block *self,
+				unsigned long action, void *arg)
+{
+	struct ipc_namespace *ns;
+
+	switch (action) {
+	case IPCNS_MEMCHANGED:   /* amount of lowmem has changed */
+		/*
+		 * It's time to recompute msgmni
+		 */
+		ns = container_of(self, struct ipc_namespace, ipcns_nb);
+		/*
+		 * No need to get a reference on the ns: the 1st job of
+		 * free_ipc_ns() is to unregister the callback routine.
+		 * blocking_notifier_chain_unregister takes the wr lock to do
+		 * it.
+		 * When this callback routine is called the rd lock is held by
+		 * blocking_notifier_call_chain.
+		 * So the ipc ns cannot be freed while we are here.
+		 */
+		recompute_msgmni(ns);
+		break;
+	default:
+		break;
+	}
+
+	return NOTIFY_OK;
+}
+
+int 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_register(&ipcns_chain, &ns->ipcns_nb);
+}
+
+int unregister_ipcns_notifier(struct ipc_namespace *ns)
+{
+	return blocking_notifier_chain_unregister(&ipcns_chain,
+						&ns->ipcns_nb);
+}
+
+int ipcns_notify(unsigned long val)
+{
+	return blocking_notifier_call_chain(&ipcns_chain, val, NULL);
+}