linuxkpi: Take const root in read-only radix tree functions

This is a preparation step for a future addition to this file. This is
also closer to what Linux does.

Reviewed by:	emaste
Sponsored by:	The FreeBSD Foundation

sys/compat/linuxkpi/common/include/linux/radix-tree.h

@@ -74,11 +74,11 @@ radix_tree_exception(void *arg)
 	return ((uintptr_t)arg & RADIX_TREE_ENTRY_MASK);
 }
 
-void	*radix_tree_lookup(struct radix_tree_root *, unsigned long);
+void	*radix_tree_lookup(const struct radix_tree_root *, unsigned long);
 void	*radix_tree_delete(struct radix_tree_root *, unsigned long);
 int	radix_tree_insert(struct radix_tree_root *, unsigned long, void *);
 int	radix_tree_store(struct radix_tree_root *, unsigned long, void **);
-bool	radix_tree_iter_find(struct radix_tree_root *, struct radix_tree_iter *, void ***);
+bool	radix_tree_iter_find(const struct radix_tree_root *, struct radix_tree_iter *, void ***);
 void	radix_tree_iter_delete(struct radix_tree_root *, struct radix_tree_iter *, void **);
 
 #endif	/* _LINUXKPI_LINUX_RADIX_TREE_H_ */

sys/compat/linuxkpi/common/src/linux_radix.c

@@ -41,7 +41,7 @@
 static MALLOC_DEFINE(M_RADIX, "radix", "Linux radix compat");
 
 static inline unsigned long
-radix_max(struct radix_tree_root *root)
+radix_max(const struct radix_tree_root *root)
 {
 	return ((1UL << (root->height * RADIX_TREE_MAP_SHIFT)) - 1UL);
 }
@@ -64,7 +64,7 @@ radix_tree_clean_root_node(struct radix_tree_root *root)
 }
 
 void *
-radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
+radix_tree_lookup(const struct radix_tree_root *root, unsigned long index)
 {
 	struct radix_tree_node *node;
 	void *item;
@@ -85,8 +85,8 @@ radix_tree_lookup(struct radix_tree_root *root, unsigned long index)
 }
 
 bool
-radix_tree_iter_find(struct radix_tree_root *root, struct radix_tree_iter *iter,
-    void ***pppslot)
+radix_tree_iter_find(const struct radix_tree_root *root,
+    struct radix_tree_iter *iter, void ***pppslot)
 {
 	struct radix_tree_node *node;
 	unsigned long index = iter->index;