dm persistent data: fix nested btree deletion

When deleting nested btrees, the code forgets to delete the innermost
btree.  The thin-metadata code serendipitously compensates for this by
claiming there is one extra layer in the tree.

This patch corrects both problems.
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-thin-metadata.c

@@ -408,7 +408,7 @@ static void __setup_btree_details(struct dm_pool_metadata *pmd)
 
 	pmd->tl_info.tm = pmd->tm;
 	pmd->tl_info.levels = 1;
-	pmd->tl_info.value_type.context = &pmd->info;
+	pmd->tl_info.value_type.context = &pmd->bl_info;
 	pmd->tl_info.value_type.size = sizeof(__le64);
 	pmd->tl_info.value_type.inc = subtree_inc;
 	pmd->tl_info.value_type.dec = subtree_dec;

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

@@ -230,6 +230,11 @@ static void pop_frame(struct del_stack *s)
 	dm_tm_unlock(s->tm, f->b);
 }
 
+static bool is_internal_level(struct dm_btree_info *info, struct frame *f)
+{
+	return f->level < (info->levels - 1);
+}
+
 int dm_btree_del(struct dm_btree_info *info, dm_block_t root)
 {
 	int r;
@@ -241,7 +246,7 @@ int dm_btree_del(struct dm_btree_info *info, dm_block_t root)
 	s->tm = info->tm;
 	s->top = -1;
 
-	r = push_frame(s, root, 1);
+	r = push_frame(s, root, 0);
 	if (r)
 		goto out;
 
@@ -267,7 +272,7 @@ int dm_btree_del(struct dm_btree_info *info, dm_block_t root)
 			if (r)
 				goto out;
 
-		} else if (f->level != (info->levels - 1)) {
+		} else if (is_internal_level(info, f)) {
 			b = value64(f->n, f->current_child);
 			f->current_child++;
 			r = push_frame(s, b, f->level + 1);