From 44d0b1903f6d2a6f409d8c83a2f2468d290618cf Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt@redhat.com>
Date: Tue, 7 May 2013 15:22:13 +0100
Subject: [PATCH] [btree] allow visitors to trap node access failures such as
 checksum error.

---
 persistent-data/data-structures/btree.h   | 15 +++++++++++++++
 persistent-data/data-structures/btree.tcc | 20 ++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/persistent-data/data-structures/btree.h b/persistent-data/data-structures/btree.h
index 0e54d3f..be64f24 100644
--- a/persistent-data/data-structures/btree.h
+++ b/persistent-data/data-structures/btree.h
@@ -331,6 +331,17 @@ namespace persistent_data {
 						leaf_node const &n) = 0;
 
 			virtual void visit_complete() {}
+
+
+			enum error_outcome {
+				EXCEPTION_HANDLED,
+				RETHROW_EXCEPTION
+			};
+
+			virtual error_outcome error_accessing_node(node_location const &l, block_address b,
+							  std::string const &what) {
+				return RETHROW_EXCEPTION;
+			}
 		};
 
 		// Walks the tree in depth first order
@@ -366,6 +377,10 @@ namespace persistent_data {
 			       btree_detail::node_location const &loc,
 			       block_address b) const;
 
+		void walk_tree_internal(visitor &visitor,
+					btree_detail::node_location const &loc,
+					block_address b) const;
+
 		typename persistent_data::transaction_manager::ptr tm_;
 		bool destroy_;
 		block_address root_;
diff --git a/persistent-data/data-structures/btree.tcc b/persistent-data/data-structures/btree.tcc
index d491700..e91670f 100644
--- a/persistent-data/data-structures/btree.tcc
+++ b/persistent-data/data-structures/btree.tcc
@@ -760,6 +760,26 @@ void
 btree<Levels, ValueTraits>::walk_tree(visitor &v,
 				      node_location const &loc,
 				      block_address b) const
+{
+	try {
+		walk_tree_internal(v, loc, b);
+
+	} catch (std::runtime_error const &e) {
+		switch (v.error_accessing_node(loc, b, e.what())) {
+		case visitor::EXCEPTION_HANDLED:
+			break;
+
+		case visitor::RETHROW_EXCEPTION:
+			throw;
+		}
+	}
+}
+
+template <unsigned Levels, typename ValueTraits>
+void
+btree<Levels, ValueTraits>::walk_tree_internal(visitor &v,
+					       node_location const &loc,
+					       block_address b) const
 {
 	using namespace btree_detail;