libsnapshot: Remove OnlineKernelSnapshotWriter.

This was never used or tested. The idea was to unify update_engine's
write paths on ISnapshotWriter. But given that legacy VAB is "legacy",
it doesn't make sense to begin refactoring that code and potentially
introducing bugs. Let's just remove this instead.

Bug: 280529365
Test: builds
Change-Id: Ie2f531bd140e183dfde4b65a144f3b4acc28e78a

fs_mgr/libsnapshot/include/libsnapshot/snapshot.h

@@ -697,10 +697,6 @@ class SnapshotManager final : public ISnapshotManager {
             LockedFile* lock, const std::optional<std::string>& source_device,
             const std::string& partition_name, const SnapshotStatus& status,
             const SnapshotPaths& paths);
-    std::unique_ptr<ISnapshotWriter> OpenKernelSnapshotWriter(
-            LockedFile* lock, const std::optional<std::string>& source_device,
-            const std::string& partition_name, const SnapshotStatus& status,
-            const SnapshotPaths& paths);
 
     // Map the base device, COW devices, and snapshot device.
     bool MapPartitionWithSnapshot(LockedFile* lock, CreateLogicalPartitionParams params,

fs_mgr/libsnapshot/include/libsnapshot/snapshot_writer.h

@@ -89,38 +89,5 @@ class CompressedSnapshotWriter final : public ISnapshotWriter {
     std::unique_ptr<CowWriter> cow_;
 };
 
-// Write directly to a dm-snapshot device.
-class OnlineKernelSnapshotWriter final : public ISnapshotWriter {
-  public:
-    OnlineKernelSnapshotWriter(const CowOptions& options);
-
-    // Set the device used for all writes.
-    void SetSnapshotDevice(android::base::unique_fd&& snapshot_fd, uint64_t cow_size);
-
-    bool Initialize() override { return true; }
-    bool InitializeAppend(uint64_t) override { return true; }
-
-    bool Finalize() override;
-    uint64_t GetCowSize() override { return cow_size_; }
-    std::unique_ptr<FileDescriptor> OpenReader() override;
-
-    // Online kernel snapshot writer doesn't care about merge sequences.
-    // So ignore.
-    bool VerifyMergeOps() const noexcept override { return true; }
-
-  protected:
-    bool EmitRawBlocks(uint64_t new_block_start, const void* data, size_t size) override;
-    bool EmitZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) override;
-    bool EmitXorBlocks(uint32_t new_block_start, const void* data, size_t size, uint32_t old_block,
-                       uint16_t offset) override;
-    bool EmitCopy(uint64_t new_block, uint64_t old_block, uint64_t num_blocks = 1) override;
-    bool EmitLabel(uint64_t label) override;
-    bool EmitSequenceData(size_t num_ops, const uint32_t* data) override;
-
-  private:
-    android::base::unique_fd snapshot_fd_;
-    uint64_t cow_size_ = 0;
-};
-
 }  // namespace snapshot
 }  // namespace android

fs_mgr/libsnapshot/snapshot.cpp

@@ -3647,12 +3647,13 @@ std::unique_ptr<ISnapshotWriter> SnapshotManager::OpenSnapshotWriter(
         return nullptr;
     }
 
-    if (status.using_snapuserd()) {
-        return OpenCompressedSnapshotWriter(lock.get(), source_device, params.GetPartitionName(),
-                                            status, paths);
+    if (!status.using_snapuserd()) {
+        LOG(ERROR) << "Can only create snapshot writers with userspace or compressed snapshots";
+        return nullptr;
     }
-    return OpenKernelSnapshotWriter(lock.get(), source_device, params.GetPartitionName(), status,
-                                    paths);
+
+    return OpenCompressedSnapshotWriter(lock.get(), source_device, params.GetPartitionName(),
+                                        status, paths);
 #endif
 }
 
@@ -3700,34 +3701,6 @@ std::unique_ptr<ISnapshotWriter> SnapshotManager::OpenCompressedSnapshotWriter(
 
     return writer;
 }
-
-std::unique_ptr<ISnapshotWriter> SnapshotManager::OpenKernelSnapshotWriter(
-        LockedFile* lock, const std::optional<std::string>& source_device,
-        [[maybe_unused]] const std::string& partition_name, const SnapshotStatus& status,
-        const SnapshotPaths& paths) {
-    CHECK(lock);
-
-    CowOptions cow_options;
-    cow_options.max_blocks = {status.device_size() / cow_options.block_size};
-
-    auto writer = std::make_unique<OnlineKernelSnapshotWriter>(cow_options);
-
-    std::string path = paths.snapshot_device.empty() ? paths.target_device : paths.snapshot_device;
-    unique_fd fd(open(path.c_str(), O_RDWR | O_CLOEXEC));
-    if (fd < 0) {
-        PLOG(ERROR) << "open failed: " << path;
-        return nullptr;
-    }
-
-    if (source_device) {
-        writer->SetSourceDevice(*source_device);
-    }
-
-    uint64_t cow_size = status.cow_partition_size() + status.cow_file_size();
-    writer->SetSnapshotDevice(std::move(fd), cow_size);
-
-    return writer;
-}
 #endif  // !defined(LIBSNAPSHOT_NO_COW_WRITE)
 
 bool SnapshotManager::UnmapUpdateSnapshot(const std::string& target_partition_name) {

fs_mgr/libsnapshot/snapshot_test.cpp

@@ -643,21 +643,38 @@ TEST_F(SnapshotTest, FirstStageMountAfterRollback) {
 TEST_F(SnapshotTest, Merge) {
     ASSERT_TRUE(AcquireLock());
 
-    static const uint64_t kDeviceSize = 1024 * 1024;
-
-    std::unique_ptr<ISnapshotWriter> writer;
-    ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize, &writer));
-
-    bool userspace_snapshots = sm->UpdateUsesUserSnapshots(lock_.get());
-
-    // Release the lock.
-    lock_ = nullptr;
+    static constexpr uint64_t kDeviceSize = 1024 * 1024;
+    static constexpr uint32_t kBlockSize = 4096;
 
     std::string test_string = "This is a test string.";
-    test_string.resize(writer->options().block_size);
-    ASSERT_TRUE(writer->AddRawBlocks(0, test_string.data(), test_string.size()));
-    ASSERT_TRUE(writer->Finalize());
-    writer = nullptr;
+    test_string.resize(kBlockSize);
+
+    bool userspace_snapshots = false;
+    if (snapuserd_required_) {
+        std::unique_ptr<ISnapshotWriter> writer;
+        ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize, &writer));
+
+        userspace_snapshots = sm->UpdateUsesUserSnapshots(lock_.get());
+
+        // Release the lock.
+        lock_ = nullptr;
+
+        ASSERT_TRUE(writer->AddRawBlocks(0, test_string.data(), test_string.size()));
+        ASSERT_TRUE(writer->Finalize());
+        writer = nullptr;
+    } else {
+        ASSERT_TRUE(PrepareOneSnapshot(kDeviceSize));
+
+        // Release the lock.
+        lock_ = nullptr;
+
+        std::string path;
+        ASSERT_TRUE(dm_.GetDmDevicePathByName("test_partition_b", &path));
+
+        unique_fd fd(open(path.c_str(), O_WRONLY));
+        ASSERT_GE(fd, 0);
+        ASSERT_TRUE(android::base::WriteFully(fd, test_string.data(), test_string.size()));
+    }
 
     // Done updating.
     ASSERT_TRUE(sm->FinishedSnapshotWrites(false));

fs_mgr/libsnapshot/snapshot_writer.cpp

@@ -149,95 +149,5 @@ bool CompressedSnapshotWriter::InitializeAppend(uint64_t label) {
     return cow_->InitializeAppend(cow_device_, label);
 }
 
-OnlineKernelSnapshotWriter::OnlineKernelSnapshotWriter(const CowOptions& options)
-    : ISnapshotWriter(options) {}
-
-void OnlineKernelSnapshotWriter::SetSnapshotDevice(android::base::unique_fd&& snapshot_fd,
-                                                   uint64_t cow_size) {
-    snapshot_fd_ = std::move(snapshot_fd);
-    cow_size_ = cow_size;
-}
-
-bool OnlineKernelSnapshotWriter::Finalize() {
-    if (fsync(snapshot_fd_.get()) < 0) {
-        PLOG(ERROR) << "fsync";
-        return false;
-    }
-    return true;
-}
-
-bool OnlineKernelSnapshotWriter::EmitRawBlocks(uint64_t new_block_start, const void* data,
-                                               size_t size) {
-    uint64_t offset = new_block_start * options_.block_size;
-    if (lseek(snapshot_fd_.get(), offset, SEEK_SET) < 0) {
-        PLOG(ERROR) << "EmitRawBlocks lseek to offset " << offset;
-        return false;
-    }
-    if (!android::base::WriteFully(snapshot_fd_, data, size)) {
-        PLOG(ERROR) << "EmitRawBlocks write";
-        return false;
-    }
-    return true;
-}
-
-bool OnlineKernelSnapshotWriter::EmitXorBlocks(uint32_t, const void*, size_t, uint32_t, uint16_t) {
-    LOG(ERROR) << "EmitXorBlocks not implemented.";
-    return false;
-}
-
-bool OnlineKernelSnapshotWriter::EmitZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) {
-    std::string zeroes(options_.block_size, 0);
-    for (uint64_t i = 0; i < num_blocks; i++) {
-        if (!EmitRawBlocks(new_block_start + i, zeroes.data(), zeroes.size())) {
-            return false;
-        }
-    }
-    return true;
-}
-
-bool OnlineKernelSnapshotWriter::EmitCopy(uint64_t new_block, uint64_t old_block,
-                                          uint64_t num_blocks) {
-    auto source_fd = GetSourceFd();
-    if (source_fd < 0) {
-        return false;
-    }
-
-    CHECK(num_blocks != 0);
-
-    for (size_t i = 0; i < num_blocks; i++) {
-        std::string buffer(options_.block_size, 0);
-        uint64_t offset = (old_block + i) * options_.block_size;
-        if (!android::base::ReadFullyAtOffset(source_fd, buffer.data(), buffer.size(), offset)) {
-            PLOG(ERROR) << "EmitCopy read";
-            return false;
-        }
-        if (!EmitRawBlocks(new_block + i, buffer.data(), buffer.size())) {
-            PLOG(ERROR) << "EmitRawBlocks failed";
-            return false;
-        }
-    }
-
-    return true;
-}
-
-bool OnlineKernelSnapshotWriter::EmitLabel(uint64_t) {
-    // Not Needed
-    return true;
-}
-
-bool OnlineKernelSnapshotWriter::EmitSequenceData(size_t, const uint32_t*) {
-    // Not Needed
-    return true;
-}
-
-std::unique_ptr<FileDescriptor> OnlineKernelSnapshotWriter::OpenReader() {
-    unique_fd fd(dup(snapshot_fd_.get()));
-    if (fd < 0) {
-        PLOG(ERROR) << "dup2 failed in OpenReader";
-        return nullptr;
-    }
-    return std::make_unique<ReadFdFileDescriptor>(std::move(fd));
-}
-
 }  // namespace snapshot
 }  // namespace android