Linux compat 2.6.37, invalidate_inodes()

In the 2.6.37 kernel the function invalidate_inodes() is no longer
exported for use by modules.  This memory management functionality
is needed to invalidate the inodes attached to a super block without
unmounting the filesystem.

Because this function still exists in the kernel and the prototype
is available is a common header all we strictly need is the symbol
address.  The address is obtained using spl_kallsyms_lookup_name()
and assigned to the variable invalidate_inodes_fn.  Then a #define
is used to replace all instances of invalidate_inodes() with a
call to the acquired address.  All the complexity is hidden behind
HAVE_INVALIDATE_INODES and invalidate_inodes() can be used as usual.

Long term we should try to get this, or another, interface made
available to modules again.

include/linux/mm_compat.h

@@ -26,6 +26,7 @@
 #define _SPL_MM_COMPAT_H
 
 #include <linux/mm.h>
+#include <linux/fs.h>
 
 /*
  * Linux 2.6.31 API Change.
@@ -43,4 +44,16 @@
 #define high_wmark_pages(z)	(z->pages_high)
 #endif
 
+/*
+ * 2.6.37 API compat,
+ * The function invalidate_inodes() is no longer exported by the kernel.
+ * The prototype however is still available which means it is safe
+ * to acquire the symbol's address using spl_kallsyms_lookup_name().
+ */
+#ifndef HAVE_INVALIDATE_INODES
+typedef int (*invalidate_inodes_t)(struct super_block *sb);
+extern invalidate_inodes_t invalidate_inodes_fn;
+#define invalidate_inodes(sb)	invalidate_inodes_fn(sb)
+#endif /* HAVE_INVALIDATE_INODES */
+
 #endif /* SPL_MM_COMPAT_H */