From a7573c7b9065aa5d5b98a13d937431eb996c58e9 Mon Sep 17 00:00:00 2001
From: Daniel Rosenberg <drosen@google.com>
Date: Fri, 30 Jul 2021 20:39:20 -0700
Subject: [PATCH] libsnapshot: Don't PrepMergeOps on resume

If we're reading up to a label, we're resuming setting up the file, and
there is no reason to expect the ops we require for sequence ops to be
present. In that case, skip prepping for merge, and return an empty
merge iterator if it is mistakenly requested.

Test: cow_api_test CowTest.ResumeSeqOp
Change-Id: Idd93bd4c4209197b9728fcb21a7191aae971b62d
---
 fs_mgr/libsnapshot/cow_api_test.cpp | 48 +++++++++++++++++++++++++++++
 fs_mgr/libsnapshot/cow_reader.cpp   |  8 ++++-
 2 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/fs_mgr/libsnapshot/cow_api_test.cpp b/fs_mgr/libsnapshot/cow_api_test.cpp
index 7e9097e3f..60663098a 100644
--- a/fs_mgr/libsnapshot/cow_api_test.cpp
+++ b/fs_mgr/libsnapshot/cow_api_test.cpp
@@ -1113,6 +1113,54 @@ TEST_F(CowTest, MissingSeqOp) {
     ASSERT_FALSE(reader.Parse(cow_->fd));
 }
 
+TEST_F(CowTest, ResumeSeqOp) {
+    CowOptions options;
+    auto writer = std::make_unique<CowWriter>(options);
+    const int seq_len = 10;
+    uint32_t sequence[seq_len];
+    for (int i = 0; i < seq_len; i++) {
+        sequence[i] = i + 1;
+    }
+
+    ASSERT_TRUE(writer->Initialize(cow_->fd));
+
+    ASSERT_TRUE(writer->AddSequenceData(seq_len, sequence));
+    ASSERT_TRUE(writer->AddZeroBlocks(1, seq_len / 2));
+    ASSERT_TRUE(writer->AddLabel(1));
+    ASSERT_TRUE(writer->AddZeroBlocks(1 + seq_len / 2, 1));
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+    auto reader = std::make_unique<CowReader>();
+    ASSERT_TRUE(reader->Parse(cow_->fd, 1));
+    auto itr = reader->GetRevMergeOpIter();
+    ASSERT_TRUE(itr->Done());
+
+    writer = std::make_unique<CowWriter>(options);
+    ASSERT_TRUE(writer->InitializeAppend(cow_->fd, 1));
+    ASSERT_TRUE(writer->AddZeroBlocks(1 + seq_len / 2, seq_len / 2));
+    ASSERT_TRUE(writer->Finalize());
+
+    ASSERT_EQ(lseek(cow_->fd, 0, SEEK_SET), 0);
+
+    reader = std::make_unique<CowReader>();
+    ASSERT_TRUE(reader->Parse(cow_->fd));
+
+    auto iter = reader->GetRevMergeOpIter();
+
+    uint64_t expected_block = 10;
+    while (!iter->Done() && expected_block > 0) {
+        ASSERT_FALSE(iter->Done());
+        const auto& op = iter->Get();
+
+        ASSERT_EQ(op.new_block, expected_block);
+
+        iter->Next();
+        expected_block--;
+    }
+    ASSERT_EQ(expected_block, 0);
+    ASSERT_TRUE(iter->Done());
+}
+
 TEST_F(CowTest, RevMergeOpItrTest) {
     CowOptions options;
     options.cluster_ops = 5;
diff --git a/fs_mgr/libsnapshot/cow_reader.cpp b/fs_mgr/libsnapshot/cow_reader.cpp
index 3f59001b3..773d978ad 100644
--- a/fs_mgr/libsnapshot/cow_reader.cpp
+++ b/fs_mgr/libsnapshot/cow_reader.cpp
@@ -34,7 +34,11 @@
 namespace android {
 namespace snapshot {
 
-CowReader::CowReader() : fd_(-1), header_(), fd_size_(0) {}
+CowReader::CowReader()
+    : fd_(-1),
+      header_(),
+      fd_size_(0),
+      merge_op_blocks_(std::make_shared<std::vector<uint32_t>>()) {}
 
 static void SHA256(const void*, size_t, uint8_t[]) {
 #if 0
@@ -150,6 +154,8 @@ bool CowReader::Parse(android::base::borrowed_fd fd, std::optional<uint64_t> lab
     if (!ParseOps(label)) {
         return false;
     }
+    // If we're resuming a write, we're not ready to merge
+    if (label.has_value()) return true;
     return PrepMergeOps();
 }