vfs: uninline full_name_hash()

.. and also use it in lookup_one_len() rather than open-coding it.

There aren't any performance-critical users, so inlining it is silly.
But it wouldn't matter if it wasn't for the fact that the word-at-a-time
dentry name patches want to conditionally replace the function, and
uninlining it sets the stage for that.

So again, this is a preparatory patch that doesn't change any semantics,
and only prepares for a much cleaner and testable word-at-a-time dentry
name accessor patch.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 61b2426..f1c7eb8 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -89,14 +89,7 @@
 }
 
 /* Compute the hash for a name string. */
-static inline unsigned int
-full_name_hash(const unsigned char *name, unsigned int len)
-{
-	unsigned long hash = init_name_hash();
-	while (len--)
-		hash = partial_name_hash(*name++, hash);
-	return end_name_hash(hash);
-}
+extern unsigned int full_name_hash(const unsigned char *, unsigned int);
 
 /*
  * Try to keep struct dentry aligned on 64 byte cachelines (this will