kho: generalize radix tree APIs

The KHO radix tree is a data structure that can track the presence or
absence of an arbitrary key, with nothing inherently tied to KHO memory
preservation tracking. This was one of the design goals of the radix
tree. This was done to enable it to be re-used by other users of KHO.

Despite that, the radix tree APIs are very closely tied to KHO memory
preservation tracking. Adding a key is done by kho_radix_add_page(),
which encodes it as a page tracking operation and takes in PFN and
order. kho_radix_del_page() does the same. These functions encode the
key internally that goes into the radix tree. kho_radix_walk_tree() does
the same by baking the PFN and order into the callback arguments.

Generalize the APIs by taking the key directly and doing the encoding at
the callers. Rename the functions to kho_radix_add_key() and
kho_radix_del_key(). In practice, this removes a line each from the
functions and moves the encoding function call to the callers.
Similarly, update kho_radix_tree_walk_callback_t to take the key
directly.

Now that key encoding is no longer an inherent part of the radix tree
and can be decided by the user, rename kho_radix_{encode,decode}_key()
to kho_{encode,decode}_radix_key(). This moves them out of the
"kho_radix_" name space into the "kho_" namespace. This emphasizes that
this is KHO's way of encoding the key for its radix tree.

Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Link: https://patch.msgid.link/20260801084833.1897543-2-pratyush@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

1 files changed, 16 insertions, 18 deletions

diff --git a/include/linux/kho_radix_tree.h b/include/linux/kho_radix_tree.h
index 84e918b96e53..9157fe08f9ce 100644
--- a/include/linux/kho_radix_tree.h
+++ b/include/linux/kho_radix_tree.h
@@ -11,15 +11,19 @@
 /**
  * DOC: Kexec Handover Radix Tree
  *
- * This is a radix tree implementation for tracking physical memory pages
- * across kexec transitions. It was developed for the KHO mechanism but is
- * designed for broader use by any subsystem that needs to preserve pages.
+ * This is a radix tree implementation for tracking numeric keys across kexec
+ * transitions. It was developed for the KHO preserved memory map but is
+ * designed for broader use by any subsystem that needs to track keys.
+ * Conceptually speaking, the data structure is similar to a set. It tracks the
+ * presence or absence of numeric keys.
  *
  * The radix tree is a multi-level tree where leaf nodes are bitmaps
- * representing individual pages. To allow pages of different sizes (orders)
+ * representing individual keys.
+ *
+ * For the KHO preserved memory map, to allow pages of different sizes (orders)
  * to be stored efficiently in a single tree, it uses a unique key encoding
- * scheme. Each key is an unsigned long that combines a page's physical
- * address and its order.
+ * scheme. Each key is an unsigned long that combines a page's physical address
+ * and its order.
  *
  * Client code is responsible for allocating the root node of the tree,
  * initializing the mutex lock, and managing its lifecycle. It must use the
@@ -34,30 +38,24 @@ struct kho_radix_tree {
 	struct mutex lock; /* protects the tree's structure and root pointer */
 };
 
-typedef int (*kho_radix_tree_walk_callback_t)(phys_addr_t phys,
-					      unsigned int order);
+typedef int (*kho_radix_tree_walk_callback_t)(unsigned long key);
 
 #ifdef CONFIG_KEXEC_HANDOVER
 
-int kho_radix_add_page(struct kho_radix_tree *tree, unsigned long pfn,
-		       unsigned int order);
-
-void kho_radix_del_page(struct kho_radix_tree *tree, unsigned long pfn,
-			unsigned int order);
-
+int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key);
+void kho_radix_del_key(struct kho_radix_tree *tree, unsigned long key);
 int kho_radix_walk_tree(struct kho_radix_tree *tree,
 			kho_radix_tree_walk_callback_t cb);
 
 #else  /* #ifdef CONFIG_KEXEC_HANDOVER */
 
-static inline int kho_radix_add_page(struct kho_radix_tree *tree, long pfn,
-				     unsigned int order)
+static inline int kho_radix_add_key(struct kho_radix_tree *tree, unsigned long key)
 {
 	return -EOPNOTSUPP;
 }
 
-static inline void kho_radix_del_page(struct kho_radix_tree *tree,
-				      unsigned long pfn, unsigned int order) { }
+static inline void kho_radix_del_key(struct kho_radix_tree *tree,
+				     unsigned long key) { }
 
 static inline int kho_radix_walk_tree(struct kho_radix_tree *tree,
 				      kho_radix_tree_walk_callback_t cb)