ima: allocating iint improvements

With IMA-appraisal's removal of the iint mutex and taking the i_mutex
instead, allocating the iint becomes a lot simplier, as we don't need
to be concerned with two processes racing to allocate the iint. This
patch cleans up and improves performance for allocating the iint.

- removed redundant double i_mutex locking
- combined iint allocation with tree search

Changelog v2:
- removed the rwlock/read_lock changes from this patch

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
diff --git a/include/linux/integrity.h b/include/linux/integrity.h
index a0c4125..66c5fe9 100644
--- a/include/linux/integrity.h
+++ b/include/linux/integrity.h
@@ -22,13 +22,14 @@
 
 /* List of EVM protected security xattrs */
 #ifdef CONFIG_INTEGRITY
-extern int integrity_inode_alloc(struct inode *inode);
+extern struct integrity_iint_cache *integrity_inode_get(struct inode *inode);
 extern void integrity_inode_free(struct inode *inode);
 
 #else
-static inline int integrity_inode_alloc(struct inode *inode)
+static inline struct integrity_iint_cache *
+				integrity_inode_get(struct inode *inode)
 {
-	return 0;
+	return NULL;
 }
 
 static inline void integrity_inode_free(struct inode *inode)