libsnapshot: Fix CHECK failure during second phase merge

This CHECK prevents a release build from resuming a two-phase merge if
the merge initially failed in the first pass.

Bug: 213031779
Test: vts_libsnapshot_test
Test: update_engine_unittests
Change-Id: I8bf00e3016546ef7039bb0b18eb977cc3dc1066a

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -396,6 +396,17 @@ class SnapshotManager final : public ISnapshotManager {
         DM_USER,
     };
 
+    // Add new public entries above this line.
+
+    // Helpers for failure injection.
+    using MergeConsistencyChecker =
+            std::function<MergeFailureCode(const std::string& name, const SnapshotStatus& status)>;
+
+    void set_merge_consistency_checker(MergeConsistencyChecker checker) {
+        merge_consistency_checker_ = checker;
+    }
+    MergeConsistencyChecker merge_consistency_checker() const { return merge_consistency_checker_; }
+
   private:
     FRIEND_TEST(SnapshotTest, CleanFirstStageMount);
     FRIEND_TEST(SnapshotTest, CreateSnapshot);
@@ -410,6 +421,7 @@ class SnapshotManager final : public ISnapshotManager {
     FRIEND_TEST(SnapshotTest, NoMergeBeforeReboot);
     FRIEND_TEST(SnapshotTest, UpdateBootControlHal);
     FRIEND_TEST(SnapshotUpdateTest, AddPartition);
+    FRIEND_TEST(SnapshotUpdateTest, ConsistencyCheckResume);
     FRIEND_TEST(SnapshotUpdateTest, DaemonTransition);
     FRIEND_TEST(SnapshotUpdateTest, DataWipeAfterRollback);
     FRIEND_TEST(SnapshotUpdateTest, DataWipeRollbackInRecovery);
@@ -811,6 +823,7 @@ class SnapshotManager final : public ISnapshotManager {
     std::unique_ptr<SnapuserdClient> snapuserd_client_;
     std::unique_ptr<LpMetadata> old_partition_metadata_;
     std::optional<bool> is_snapshot_userspace_;
+    MergeConsistencyChecker merge_consistency_checker_;
 };
 
 }  // namespace snapshot

fs_mgr/libsnapshot/snapshot.cpp

@@ -87,6 +87,8 @@ static constexpr char kBootIndicatorPath[] = "/metadata/ota/snapshot-boot";
 static constexpr char kRollbackIndicatorPath[] = "/metadata/ota/rollback-indicator";
 static constexpr auto kUpdateStateCheckInterval = 2s;
 
+MergeFailureCode CheckMergeConsistency(const std::string& name, const SnapshotStatus& status);
+
 // Note: IImageManager is an incomplete type in the header, so the default
 // destructor doesn't work.
 SnapshotManager::~SnapshotManager() {}
@@ -116,7 +118,9 @@ std::unique_ptr<SnapshotManager> SnapshotManager::NewForFirstStageMount(IDeviceI
 }
 
 SnapshotManager::SnapshotManager(IDeviceInfo* device)
-    : dm_(device->GetDeviceMapper()), device_(device), metadata_dir_(device_->GetMetadataDir()) {}
+    : dm_(device->GetDeviceMapper()), device_(device), metadata_dir_(device_->GetMetadataDir()) {
+    merge_consistency_checker_ = android::snapshot::CheckMergeConsistency;
+}
 
 static std::string GetCowName(const std::string& snapshot_name) {
     return snapshot_name + "-cow";
@@ -1329,14 +1333,20 @@ MergeFailureCode SnapshotManager::CheckMergeConsistency(LockedFile* lock, const
                                                         const SnapshotStatus& status) {
     CHECK(lock);
 
+    return merge_consistency_checker_(name, status);
+}
+
+MergeFailureCode CheckMergeConsistency(const std::string& name, const SnapshotStatus& status) {
     if (!status.compression_enabled()) {
         // Do not try to verify old-style COWs yet.
         return MergeFailureCode::Ok;
     }
 
+    auto& dm = DeviceMapper::Instance();
+
     std::string cow_image_name = GetMappedCowDeviceName(name, status);
     std::string cow_image_path;
-    if (!dm_.GetDmDevicePathByName(cow_image_name, &cow_image_path)) {
+    if (!dm.GetDmDevicePathByName(cow_image_name, &cow_image_path)) {
         LOG(ERROR) << "Failed to get path for cow device: " << cow_image_name;
         return MergeFailureCode::GetCowPathConsistencyCheck;
     }
@@ -1400,9 +1410,11 @@ MergeFailureCode SnapshotManager::MergeSecondPhaseSnapshots(LockedFile* lock) {
     }
 
     SnapshotUpdateStatus update_status = ReadSnapshotUpdateStatus(lock);
-    CHECK(update_status.state() == UpdateState::Merging);
+    CHECK(update_status.state() == UpdateState::Merging ||
+          update_status.state() == UpdateState::MergeFailed);
     CHECK(update_status.merge_phase() == MergePhase::FIRST_PHASE);
 
+    update_status.set_state(UpdateState::Merging);
     update_status.set_merge_phase(MergePhase::SECOND_PHASE);
     if (!WriteSnapshotUpdateStatus(lock, update_status)) {
         return MergeFailureCode::WriteStatus;

fs_mgr/libsnapshot/snapshot_test.cpp

@@ -1394,6 +1394,93 @@ TEST_F(SnapshotUpdateTest, SpaceSwapUpdate) {
     }
 }
 
+// Test that a transient merge consistency check failure can resume properly.
+TEST_F(SnapshotUpdateTest, ConsistencyCheckResume) {
+    if (!ShouldUseCompression()) {
+        // b/179111359
+        GTEST_SKIP() << "Skipping Virtual A/B Compression test";
+    }
+
+    auto old_sys_size = GetSize(sys_);
+    auto old_prd_size = GetSize(prd_);
+
+    // Grow |sys| but shrink |prd|.
+    SetSize(sys_, old_sys_size * 2);
+    sys_->set_estimate_cow_size(8_MiB);
+    SetSize(prd_, old_prd_size / 2);
+    prd_->set_estimate_cow_size(1_MiB);
+
+    AddOperationForPartitions();
+
+    ASSERT_TRUE(sm->BeginUpdate());
+    ASSERT_TRUE(sm->CreateUpdateSnapshots(manifest_));
+    ASSERT_TRUE(WriteSnapshotAndHash("sys_b"));
+    ASSERT_TRUE(WriteSnapshotAndHash("vnd_b"));
+    ASSERT_TRUE(ShiftAllSnapshotBlocks("prd_b", old_prd_size));
+
+    sync();
+
+    // Assert that source partitions aren't affected.
+    for (const auto& name : {"sys_a", "vnd_a", "prd_a"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    ASSERT_TRUE(sm->FinishedSnapshotWrites(false));
+
+    // Simulate shutting down the device.
+    ASSERT_TRUE(UnmapAll());
+
+    // After reboot, init does first stage mount.
+    auto init = NewManagerForFirstStageMount("_b");
+    ASSERT_NE(init, nullptr);
+    ASSERT_TRUE(init->NeedSnapshotsInFirstStageMount());
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Check that the target partitions have the same content.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name));
+    }
+
+    auto old_checker = init->merge_consistency_checker();
+
+    init->set_merge_consistency_checker(
+            [](const std::string&, const SnapshotStatus&) -> MergeFailureCode {
+                return MergeFailureCode::WrongMergeCountConsistencyCheck;
+            });
+
+    // Initiate the merge and wait for it to be completed.
+    ASSERT_TRUE(init->InitiateMerge());
+    ASSERT_EQ(init->IsSnapuserdRequired(), ShouldUseUserspaceSnapshots());
+    {
+        // Check that the merge phase is FIRST_PHASE until at least one call
+        // to ProcessUpdateState() occurs.
+        ASSERT_TRUE(AcquireLock());
+        auto local_lock = std::move(lock_);
+        auto status = init->ReadSnapshotUpdateStatus(local_lock.get());
+        ASSERT_EQ(status.merge_phase(), MergePhase::FIRST_PHASE);
+    }
+
+    // Merge should have failed.
+    ASSERT_EQ(UpdateState::MergeFailed, init->ProcessUpdateState());
+
+    // Simulate shutting down the device and creating partitions again.
+    ASSERT_TRUE(UnmapAll());
+
+    // Restore the checker.
+    init->set_merge_consistency_checker(std::move(old_checker));
+
+    ASSERT_TRUE(init->CreateLogicalAndSnapshotPartitions("super", snapshot_timeout_));
+
+    // Complete the merge.
+    ASSERT_EQ(UpdateState::MergeCompleted, init->ProcessUpdateState());
+
+    // Check that the target partitions have the same content after the merge.
+    for (const auto& name : {"sys_b", "vnd_b", "prd_b"}) {
+        ASSERT_TRUE(IsPartitionUnchanged(name))
+                << "Content of " << name << " changes after the merge";
+    }
+}
+
 // Test that if new system partitions uses empty space in super, that region is not snapshotted.
 TEST_F(SnapshotUpdateTest, DirectWriteEmptySpace) {
     GTEST_SKIP() << "b/141889746";