include/linux/memory.h: implement register_hotmemory_notifier()

When CONFIG_MEMORY_HOTPLUG=n, we don't want the memory-hotplug notifier
handlers to be included in the .o files, for space reasons.

The existing hotplug_memory_notifier() tries to handle this but testing
with gcc-4.4.4 shows that it doesn't work - the hotplug functions are
still present in the .o files.

So implement a new register_hotmemory_notifier() which is a copy of
register_hotcpu_notifier(), and which actually works as desired.
hotplug_memory_notifier() and register_memory_notifier() callsites
should be converted to use this new register_hotmemory_notifier().

While we're there, let's repair the existing hotplug_memory_notifier():
it simply stomps on the register_memory_notifier() return value, so
well-behaved code cannot check for errors.  Apparently non of the
existing callers were well-behaved :(

Cc: Andrew Shewmaker <agshew@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index d65746efc954..d14a4c362465 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -47,8 +47,11 @@
  * runtime initialization.
  */
 
+typedef	int (*notifier_fn_t)(struct notifier_block *nb,
+			unsigned long action, void *data);
+
 struct notifier_block {
-	int (*notifier_call)(struct notifier_block *, unsigned long, void *);
+	notifier_fn_t notifier_call;
 	struct notifier_block __rcu *next;
 	int priority;
 };