From 2e95ace82b91d38de8079b25d868043f6e427851 Mon Sep 17 00:00:00 2001
From: Gyuho Lee <gyuhox@gmail.com>
Date: Sun, 17 Dec 2017 23:32:55 -0800
Subject: [PATCH] mvcc: fetch revisions with current revision, not 0, in
 HashByRev

It was getting revisions with "atRev==0", which makes
"available" from "keep" method always empty since
"walk" on "keyIndex" only returns true.

"available" should be populated with all revisions to be
kept if the compaction happens with the given revision.
But, "available" was being empty when "kvindex.Keep(0)"
since it's always the case that "rev.main > atRev==0".

Fix https://github.com/coreos/etcd/issues/9022.

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>
---
 mvcc/kvstore.go      |  7 +++----
 mvcc/kvstore_test.go | 29 +++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/mvcc/kvstore.go b/mvcc/kvstore.go
index 1a695e3ab..486365a92 100644
--- a/mvcc/kvstore.go
+++ b/mvcc/kvstore.go
@@ -175,6 +175,9 @@ func (s *store) HashByRev(rev int64) (hash uint32, currentRev int64, compactRev
 		return 0, currentRev, 0, ErrFutureRev
 	}
 
+	if rev == 0 {
+		rev = currentRev
+	}
 	keep := s.kvindex.Keep(rev)
 
 	tx := s.b.ReadTx()
@@ -182,10 +185,6 @@ func (s *store) HashByRev(rev int64) (hash uint32, currentRev int64, compactRev
 	defer tx.Unlock()
 	s.mu.RUnlock()
 
-	if rev == 0 {
-		rev = currentRev
-	}
-
 	upper := revision{main: rev + 1}
 	lower := revision{main: compactRev + 1}
 	h := crc32.New(crc32.MakeTable(crc32.Castagnoli))
diff --git a/mvcc/kvstore_test.go b/mvcc/kvstore_test.go
index 35621d7d9..6a0e1d3b1 100644
--- a/mvcc/kvstore_test.go
+++ b/mvcc/kvstore_test.go
@@ -583,6 +583,35 @@ func TestHashKVWhenCompacting(t *testing.T) {
 	}
 }
 
+// TestHashKVZeroRevision ensures that "HashByRev(0)" computes
+// correct hash value with latest revision.
+func TestHashKVZeroRevision(t *testing.T) {
+	b, tmpPath := backend.NewDefaultTmpBackend()
+	s := NewStore(b, &lease.FakeLessor{}, nil)
+	defer os.Remove(tmpPath)
+
+	rev := 1000
+	for i := 2; i <= rev; i++ {
+		s.Put([]byte("foo"), []byte(fmt.Sprintf("bar%d", i)), lease.NoLease)
+	}
+	if _, err := s.Compact(int64(rev / 2)); err != nil {
+		t.Fatal(err)
+	}
+
+	hash1, _, _, err := s.HashByRev(int64(rev))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var hash2 uint32
+	hash2, _, _, err = s.HashByRev(0)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hash1 != hash2 {
+		t.Errorf("hash %d (rev %d) != hash %d (rev 0)", hash1, rev, hash2)
+	}
+}
+
 func TestTxnPut(t *testing.T) {
 	// assign arbitrary size
 	bytesN := 30