From 4a2b112e98fe4c66f805eb690bfe1ae7ba342e5b Mon Sep 17 00:00:00 2001
From: Ming-Hung Tsai <mtsai@redhat.com>
Date: Thu, 19 Aug 2021 18:38:23 +0800
Subject: [PATCH 2/3] [thin_repair/thin_dump] Change the label type for empty
 leaves

Empty leaves now are treated as bottom-level leaves, so that empty
devices could be recovered.

(cherry picked from commit d3f796f5e35162b0867ee2ba8de781f14ad35c61)
---
 functional-tests/thin-functional-tests.scm | 53 +++++++++++++++++++++++++++++-
 thin-provisioning/metadata_dumper.cc       |  8 +++++
 2 files changed, 60 insertions(+), 1 deletion(-)

diff --git a/functional-tests/thin-functional-tests.scm b/functional-tests/thin-functional-tests.scm
index fcabddf..d06a5a3 100644
--- a/functional-tests/thin-functional-tests.scm
+++ b/functional-tests/thin-functional-tests.scm
@@ -14,7 +14,8 @@
     (temp-file)
     (thin metadata)
     (thin xml)
-    (srfi s8 receive))
+    (srfi s8 receive)
+    (xml))
 
   (define-tool thin-check)
   (define-tool thin-delta)
@@ -96,6 +97,32 @@
   ;; to run.
   (define (register-thin-tests) #t)
 
+  ;; XML of metadata with empty thins
+  (define xml-with-empty-thins
+    (fmt #f
+      (tag 'superblock `((uuid . "")
+                         (time . 0)
+                         (transaction . 1)
+                         (flags . 0)
+                         (version . 2)
+                         (data-block-size . 128)
+                         (nr-data-blocks . 1024))
+        (tag 'device `((dev-id . 1)
+                       (mapped-blocks . 16)
+                       (transaction . 0)
+                       (creation-time . 0)
+                       (snap-time . 0))
+          (tag 'range-mapping  `((origin-begin . 0)
+                                 (data-begin . 0)
+                                 (length . 16)
+                                 (time . 0))))
+        (tag 'device `((dev-id . 2)
+                       (mapped-blocks . 0)
+                       (transaction . 0)
+                       (creation-time . 0)
+                       (snap-time . 0))
+          " "))))
+
   ;;;-----------------------------------------------------------
   ;;; thin_check scenarios
   ;;;-----------------------------------------------------------
@@ -376,6 +403,17 @@
       (run-fail-rcv (_ stderr) (thin-dump "--repair" "--transaction-id=5" "--data-block-size=128" md)
         (assert-matches ".*nr data blocks.*" stderr))))
 
+  (define-scenario (thin-dump repair-superblock with-empty-devices)
+    "metadata with empty devices could be recovered"
+    (with-temp-file-sized ((md "thin.bin" (meg 4)))
+      (with-temp-file-containing ((xml "thin.xml" xml-with-empty-thins))
+        (run-ok (thin-restore "-i" xml "-o" md)))
+      (run-ok-rcv (expected-xml _) (thin-dump md)
+        (damage-superblock md)
+        (run-ok-rcv (repaired-xml stderr) (thin-dump "--repair" "--transaction-id=1" "--data-block-size=128" "--nr-data-blocks=1024" md)
+          (assert-eof stderr)
+          (assert-equal expected-xml repaired-xml)))))
+
   ;;;-----------------------------------------------------------
   ;;; thin_rmap scenarios
   ;;;-----------------------------------------------------------
@@ -572,6 +610,19 @@
         (run-fail-rcv (_ stderr) (thin-repair "--transaction-id=5" "--data-block-size=128" "-i" md1 "-o" md2)
           (assert-matches ".*nr data blocks.*" stderr)))))
 
+  (define-scenario (thin-repair superblock with-empty-devices)
+    "metadata with empty devices could be recovered"
+    (with-temp-file-sized ((md1 "thin.bin" (meg 4)))
+      (with-temp-file-containing ((xml "thin.xml" xml-with-empty-thins))
+        (run-ok (thin-restore "-i" xml "-o" md1)))
+      (run-ok-rcv (expected-xml _) (thin-dump md1)
+        (damage-superblock md1)
+        (with-empty-metadata (md2)
+          (run-ok-rcv (_ stderr) (thin-repair "--transaction-id=1" "--data-block-size=128" "--nr-data-blocks=1024" "-i" md1 "-o" md2)
+            (assert-eof stderr))
+          (run-ok-rcv (repaired-xml stderr) (thin-dump md2)
+            (assert-eof stderr)
+            (assert-equal expected-xml repaired-xml))))))
 
   ;;;-----------------------------------------------------------
   ;;; thin_metadata_pack scenarios
diff --git a/thin-provisioning/metadata_dumper.cc b/thin-provisioning/metadata_dumper.cc
index 37c6969..d169c27 100644
--- a/thin-provisioning/metadata_dumper.cc
+++ b/thin-provisioning/metadata_dumper.cc
@@ -438,6 +438,14 @@ namespace {
 		// in the bottom 24 bits.  This means every block/time apart from block 0
 		// will result in a value that's outside the range of the metadata device.
 		bool is_top_level(node_ref<uint64_traits> &n) {
+			// A leaf node of value-size 8 and without mappings should be
+			// treated as a bottom-level leaf, so that it could be referenced
+			// by top-level nodes, if any. On the other hand, an empty
+			// top-level leaf doesn't help repairing.
+			if (!n.get_nr_entries()) {
+				return false;
+			}
+
 			auto nr_metadata_blocks = bm_.get_nr_blocks();
 
 			for (unsigned i = 0; i < n.get_nr_entries(); i++)
-- 
1.8.3.1