From 24931b3bda7f1c7cb9bd472cdc8dc3c7c401b960 Mon Sep 17 00:00:00 2001
From: Joe Thornber <ejt@redhat.com>
Date: Wed, 4 Oct 2017 11:43:13 +0100
Subject: [PATCH] [thin_check] --override-mapping-root

---
 man8/thin_check.txt             |  6 ++++++
 thin-provisioning/thin_check.cc | 20 ++++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/man8/thin_check.txt b/man8/thin_check.txt
index 90ea334..1aae63e 100644
--- a/man8/thin_check.txt
+++ b/man8/thin_check.txt
@@ -33,6 +33,12 @@ OPTIONS
     is needed to fix any issues. After thin_repair succeeded, you may run
     thin_check again.
 
+  --override-mapping-root <block>	Specify a mapping root to use.
+
+    Don't use this.  This overrides what's specified in the superblock.  Only
+    use this if you really understand the metadata format and are trying to
+    recover damaged metadata.
+
 EXAMPLE
   Analyses thin provisioning metadata on logical volume /dev/vg/metadata:
 
diff --git a/thin-provisioning/thin_check.cc b/thin-provisioning/thin_check.cc
index dac3b01..cb3e8df 100644
--- a/thin-provisioning/thin_check.cc
+++ b/thin-provisioning/thin_check.cc
@@ -20,6 +20,9 @@
 #include <getopt.h>
 #include <libgen.h>
 
+#include <boost/lexical_cast.hpp>
+#include <boost/optional.hpp>
+
 #include "version.h"
 
 #include "base/application.h"
@@ -168,6 +171,7 @@ namespace {
 		bool ignore_non_fatal_errors;
 
 		bool quiet;
+		boost::optional<block_address> override_mapping_root;
 		bool clear_needs_check_flag_on_success;
 	};
 
@@ -208,6 +212,11 @@ namespace {
 			out << "This looks like XML.  thin_check only checks the binary metadata format." << end_message();
 	}
 
+	block_address mapping_root(superblock_detail::superblock const &sb, flags const &fs)
+	{
+		return fs.override_mapping_root ? *fs.override_mapping_root : sb.data_mapping_root_;
+	}
+
 	error_state metadata_check(string const &path, flags fs) {
 		nested_output out(cerr, 2);
 		if (fs.quiet)
@@ -253,7 +262,7 @@ namespace {
 			out << "examining top level of mapping tree" << end_message();
 			{
 				nested_output::nest _ = out.push();
-				dev_tree dtree(*tm, sb.data_mapping_root_,
+				dev_tree dtree(*tm, mapping_root(sb, fs),
 					       mapping_tree_detail::mtree_traits::ref_counter(tm));
 				check_mapping_tree(dtree, mapping_rep);
 			}
@@ -262,7 +271,7 @@ namespace {
 			out << "examining mapping tree" << end_message();
 			{
 				nested_output::nest _ = out.push();
-				mapping_tree mtree(*tm, sb.data_mapping_root_,
+				mapping_tree mtree(*tm, mapping_root(sb, fs),
 						   mapping_tree_detail::block_traits::ref_counter(tm->get_sm()));
 				check_mapping_tree(mtree, mapping_rep);
 			}
@@ -332,6 +341,7 @@ thin_check_cmd::usage(std::ostream &out) const
 	    << "  {-q|--quiet}" << endl
 	    << "  {-h|--help}" << endl
 	    << "  {-V|--version}" << endl
+	    << "  {--override-mapping-root}" << endl
 	    << "  {--clear-needs-check-flag}" << endl
 	    << "  {--ignore-non-fatal-errors}" << endl
 	    << "  {--skip-mappings}" << endl
@@ -353,6 +363,7 @@ thin_check_cmd::run(int argc, char **argv)
 		{ "skip-mappings", no_argument, NULL, 2},
 		{ "ignore-non-fatal-errors", no_argument, NULL, 3},
 		{ "clear-needs-check-flag", no_argument, NULL, 4 },
+		{ "override-mapping-root", required_argument, NULL, 5},
 		{ NULL, no_argument, NULL, 0 }
 	};
 
@@ -392,6 +403,11 @@ thin_check_cmd::run(int argc, char **argv)
 			fs.clear_needs_check_flag_on_success = true;
 			break;
 
+		case 5:
+			// override-mapping-root
+			fs.override_mapping_root = boost::lexical_cast<uint64_t>(optarg);
+			break;
+
 		default:
 			usage(cerr);
 			return 1;