Some architecture need to maintain a kmem cache for thread info
structures. (next patch adds that to powerpc to fix an alignment
problem).

There is no good arch callback to use to initialize that cache
that I can find, so this adds a new one and adds an empty macro
for when it's not implemented.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

So we have the choice here between:

 - the ifdef on the func name that I did, consistent with what
I did before for iomap, which iirc Linus liked

 - add some more ARCH_HAS_* or HAVE_* (yuck)

 - add an empty definition to all archs .h (pain in the neck but I
can do it, though it will be an annoying patch to keep around)

 - do a weak function (will slightly bloat everybody for no good reason)

So unless there is strong complaints, I'd like to stick to my
current approach.

 include/linux/sched.h |    4 ++++
 init/main.c           |    1 +
 2 files changed, 5 insertions(+)

--- linux-work.orig/init/main.c	2008-04-10 13:11:06.000000000 +1000
+++ linux-work/init/main.c	2008-04-10 13:11:19.000000000 +1000

@@ -623,6 +623,7 @@ asmlinkage void __init start_kernel(void
 	if (efi_enabled)
 		efi_enter_virtual_mode();
 #endif
+	thread_info_cache_init();
 	fork_init(num_physpages);
 	proc_caches_init();
 	buffer_init();

Index: linux-work/include/linux/sched.h
===================================================================

--- linux-work.orig/include/linux/sched.h	2008-04-10 13:11:44.000000000 +1000
+++ linux-work/include/linux/sched.h	2008-04-10 13:12:05.000000000 +1000

@@ -1893,6 +1893,10 @@ static inline unsigned long *end_of_stac
 
 #endif
 
+#ifndef thread_info_cache_init
+#define thread_info_cache_init	do { } while(0)
+#endif