ceph: add dir_layout to inode

Add a ceph_dir_layout to the inode, and calculate dentry hash values based
on the parent directory's specified dir_hash function.  This is needed
because the old default Linux dcache hash function is extremely week and
leads to a poor distribution of files among dir fragments.

Signed-off-by: Sage Weil <sage@newdream.net>

net/ceph/ceph_hash.c

@@ -1,5 +1,6 @@
 
 #include <linux/ceph/types.h>
+#include <linux/module.h>
 
 /*
  * Robert Jenkin's hash function.
@@ -104,6 +105,7 @@ unsigned ceph_str_hash(int type, const char *s, unsigned len)
 		return -1;
 	}
 }
+EXPORT_SYMBOL(ceph_str_hash);
 
 const char *ceph_str_hash_name(int type)
 {
@@ -116,3 +118,4 @@ const char *ceph_str_hash_name(int type)
 		return "unknown";
 	}
 }
+EXPORT_SYMBOL(ceph_str_hash_name);