dm persistent data: add btree_walk

Add dm_btree_walk to iterate through the contents of a btree.
This will be used by the dm cache target.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/persistent-data/dm-btree-internal.h

@@ -64,6 +64,7 @@ struct ro_spine {
 void init_ro_spine(struct ro_spine *s, struct dm_btree_info *info);
 int exit_ro_spine(struct ro_spine *s);
 int ro_step(struct ro_spine *s, dm_block_t new_child);
+void ro_pop(struct ro_spine *s);
 struct btree_node *ro_node(struct ro_spine *s);
 
 struct shadow_spine {

drivers/md/persistent-data/dm-btree-spine.c

@@ -164,6 +164,13 @@ int ro_step(struct ro_spine *s, dm_block_t new_child)
 	return r;
 }
 
+void ro_pop(struct ro_spine *s)
+{
+	BUG_ON(!s->count);
+	--s->count;
+	unlock_block(s->info, s->nodes[s->count]);
+}
+
 struct btree_node *ro_node(struct ro_spine *s)
 {
 	struct dm_block *block;

drivers/md/persistent-data/dm-btree.c

@@ -807,3 +807,55 @@ int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
 	return r ? r : count;
 }
 EXPORT_SYMBOL_GPL(dm_btree_find_highest_key);
+
+/*
+ * FIXME: We shouldn't use a recursive algorithm when we have limited stack
+ * space.  Also this only works for single level trees.
+ */
+static int walk_node(struct ro_spine *s, dm_block_t block,
+		     int (*fn)(void *context, uint64_t *keys, void *leaf),
+		     void *context)
+{
+	int r;
+	unsigned i, nr;
+	struct btree_node *n;
+	uint64_t keys;
+
+	r = ro_step(s, block);
+	n = ro_node(s);
+
+	nr = le32_to_cpu(n->header.nr_entries);
+	for (i = 0; i < nr; i++) {
+		if (le32_to_cpu(n->header.flags) & INTERNAL_NODE) {
+			r = walk_node(s, value64(n, i), fn, context);
+			if (r)
+				goto out;
+		} else {
+			keys = le64_to_cpu(*key_ptr(n, i));
+			r = fn(context, &keys, value_ptr(n, i));
+			if (r)
+				goto out;
+		}
+	}
+
+out:
+	ro_pop(s);
+	return r;
+}
+
+int dm_btree_walk(struct dm_btree_info *info, dm_block_t root,
+		  int (*fn)(void *context, uint64_t *keys, void *leaf),
+		  void *context)
+{
+	int r;
+	struct ro_spine spine;
+
+	BUG_ON(info->levels > 1);
+
+	init_ro_spine(&spine, info);
+	r = walk_node(&spine, root, fn, context);
+	exit_ro_spine(&spine);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(dm_btree_walk);

drivers/md/persistent-data/dm-btree.h

@@ -142,4 +142,13 @@ int dm_btree_remove(struct dm_btree_info *info, dm_block_t root,
 int dm_btree_find_highest_key(struct dm_btree_info *info, dm_block_t root,
 			      uint64_t *result_keys);
 
+/*
+ * Iterate through the a btree, calling fn() on each entry.
+ * It only works for single level trees and is internally recursive, so
+ * monitor stack usage carefully.
+ */
+int dm_btree_walk(struct dm_btree_info *info, dm_block_t root,
+		  int (*fn)(void *context, uint64_t *keys, void *leaf),
+		  void *context);
+
 #endif	/* _LINUX_DM_BTREE_H */