libsnapshot:snapuserd: Read the cow_operation in reverse order (d0819569) · Commits · e / os / android_system_core

fs_mgr/libsnapshot/cow_reader.cpp

+36 −0

Original line number	Diff line number	Diff line
		@@ -246,10 +246,46 @@ const CowOperation& CowOpIter::Get() {
		return (*op_iter_);
		}

		class CowOpReverseIter final : public ICowOpReverseIter {
		public:
		explicit CowOpReverseIter(std::shared_ptr<std::vector<CowOperation>> ops);

		bool Done() override;
		const CowOperation& Get() override;
		void Next() override;

		private:
		std::shared_ptr<std::vector<CowOperation>> ops_;
		std::vector<CowOperation>::reverse_iterator op_riter_;
		};

		CowOpReverseIter::CowOpReverseIter(std::shared_ptr<std::vector<CowOperation>> ops) {
		ops_ = ops;
		op_riter_ = ops_.get()->rbegin();
		}

		bool CowOpReverseIter::Done() {
		return op_riter_ == ops_.get()->rend();
		}

		void CowOpReverseIter::Next() {
		CHECK(!Done());
		op_riter_++;
		}

		const CowOperation& CowOpReverseIter::Get() {
		CHECK(!Done());
		return (*op_riter_);
		}

		std::unique_ptr<ICowOpIter> CowReader::GetOpIter() {
		return std::make_unique<CowOpIter>(ops_);
		}

		std::unique_ptr<ICowOpReverseIter> CowReader::GetRevOpIter() {
		return std::make_unique<CowOpReverseIter>(ops_);
		}

		bool CowReader::GetRawBytes(uint64_t offset, void* buffer, size_t len, size_t* read) {
		// Validate the offset, taking care to acknowledge possible overflow of offset+len.
		if (offset < sizeof(header_) \|\| offset >= fd_size_ - sizeof(footer_) \|\| len >= fd_size_ \|\|

fs_mgr/libsnapshot/include/libsnapshot/cow_reader.h

+23 −1

Original line number	Diff line number	Diff line
		@@ -26,6 +26,7 @@ namespace android {
		namespace snapshot {

		class ICowOpIter;
		class ICowOpReverseIter;

		// A ByteSink object handles requests for a buffer of a specific size. It
		// always owns the underlying buffer. It's designed to minimize potential
		@@ -73,6 +74,9 @@ class ICowReader {
		// Return an iterator for retrieving CowOperation entries.
		virtual std::unique_ptr<ICowOpIter> GetOpIter() = 0;

		// Return an reverse iterator for retrieving CowOperation entries.
		virtual std::unique_ptr<ICowOpReverseIter> GetRevOpIter() = 0;

		// Get decoded bytes from the data section, handling any decompression.
		// All retrieved data is passed to the sink.
		virtual bool ReadData(const CowOperation& op, IByteSink* sink) = 0;
		@@ -93,6 +97,21 @@ class ICowOpIter {
		virtual void Next() = 0;
		};

		// Reverse Iterate over a sequence of COW operations.
		class ICowOpReverseIter {
		public:
		virtual ~ICowOpReverseIter() {}

		// True if there are more items to read, false otherwise.
		virtual bool Done() = 0;

		// Read the current operation.
		virtual const CowOperation& Get() = 0;

		// Advance to the next item.
		virtual void Next() = 0;
		};

		class CowReader : public ICowReader {
		public:
		CowReader();
		@@ -107,8 +126,11 @@ class CowReader : public ICowReader {

		// Create a CowOpIter object which contains footer_.num_ops
		// CowOperation objects. Get() returns a unique CowOperation object
		// whose lifetime depends on the CowOpIter object
		// whose lifetime depends on the CowOpIter object; the return
		// value of these will never be null.
		std::unique_ptr<ICowOpIter> GetOpIter() override;
		std::unique_ptr<ICowOpReverseIter> GetRevOpIter() override;

		bool ReadData(const CowOperation& op, IByteSink* sink) override;

		bool GetRawBytes(uint64_t offset, void* buffer, size_t len, size_t* read);

fs_mgr/libsnapshot/include/libsnapshot/snapuserd.h

+9 −5

Original line number	Diff line number	Diff line
		@@ -24,6 +24,7 @@
		#include <limits>
		#include <string>
		#include <thread>
		#include <unordered_map>
		#include <vector>

		#include <android-base/file.h>
		@@ -69,6 +70,9 @@ class Snapuserd final {

		bool Init();
		int Run();
		const std::string& GetControlDevicePath() { return control_device_; }

		private:
		int ReadDmUserHeader();
		int WriteDmUserPayload(size_t size);
		int ConstructKernelCowHeader();
		@@ -76,10 +80,9 @@ class Snapuserd final {
		int ZerofillDiskExceptions(size_t read_size);
		int ReadDiskExceptions(chunk_t chunk, size_t size);
		int ReadData(chunk_t chunk, size_t size);
		bool IsChunkIdMetadata(chunk_t chunk);
		chunk_t GetNextAllocatableChunkId(chunk_t chunk);

		const std::string& GetControlDevicePath() { return control_device_; }

		private:
		int ProcessReplaceOp(const CowOperation* cow_op);
		int ProcessCopyOp(const CowOperation* cow_op);
		int ProcessZeroOp();
		@@ -95,15 +98,16 @@ class Snapuserd final {
		uint32_t exceptions_per_area_;

		std::unique_ptr<ICowOpIter> cowop_iter_;
		std::unique_ptr<ICowOpReverseIter> cowop_riter_;
		std::unique_ptr<CowReader> reader_;

		// Vector of disk exception which is a
		// mapping of old-chunk to new-chunk
		std::vector<std::unique_ptr<uint8_t[]>> vec_;

		// Index - Chunk ID
		// Key - Chunk ID
		// Value - cow operation
		std::vector<const CowOperation*> chunk_vec_;
		std::unordered_map<chunk_t, const CowOperation*> chunk_map_;

		bool metadata_read_done_;
		BufferSink bufsink_;

fs_mgr/libsnapshot/snapuserd.cpp

+65 −58

Original line number	Diff line number	Diff line
		@@ -159,7 +159,7 @@ int Snapuserd::ReadData(chunk_t chunk, size_t size) {
		CHECK((read_size & (BLOCK_SIZE - 1)) == 0);

		while (read_size > 0) {
		const CowOperation* cow_op = chunk_vec_[chunk_key];
		const CowOperation* cow_op = chunk_map_[chunk_key];
		CHECK(cow_op != nullptr);
		int result;

		@@ -202,6 +202,8 @@ int Snapuserd::ReadData(chunk_t chunk, size_t size) {
		// are contiguous
		chunk_key += 1;

		if (cow_op->type == kCowCopyOp) CHECK(read_size == 0);

		// This is similar to the way when chunk IDs were assigned
		// in ReadMetadata().
		//
		@@ -287,6 +289,24 @@ int Snapuserd::ReadDiskExceptions(chunk_t chunk, size_t read_size) {
		return size;
		}

		bool Snapuserd::IsChunkIdMetadata(chunk_t chunk) {
		uint32_t stride = exceptions_per_area_ + 1;
		lldiv_t divresult = lldiv(chunk, stride);

		return divresult.rem == NUM_SNAPSHOT_HDR_CHUNKS;
		}

		// Find the next free chunk-id to be assigned. Check if the next free
		// chunk-id represents a metadata page. If so, skip it.
		chunk_t Snapuserd::GetNextAllocatableChunkId(chunk_t chunk) {
		chunk_t next_chunk = chunk + 1;

		if (IsChunkIdMetadata(next_chunk)) {
		next_chunk += 1;
		}
		return next_chunk;
		}

		/*
		* Read the metadata from COW device and
		* construct the metadata as required by the kernel.
		@@ -304,12 +324,26 @@ int Snapuserd::ReadDiskExceptions(chunk_t chunk, size_t read_size) {
		* This represents the old_chunk in the kernel COW format
		* 4: We need to assign new_chunk for a corresponding old_chunk
		* 5: The algorithm is similar to how kernel assigns chunk number
		* while creating exceptions.
		* while creating exceptions. However, there are few cases
		* which needs to be addressed here:
		* a: During merge process, kernel scans the metadata page
		* from backwards when merge is initiated. Since, we need
		* to make sure that the merge ordering follows our COW format,
		* we read the COW operation from backwards and populate the
		* metadata so that when kernel starts the merging from backwards,
		* those ops correspond to the beginning of our COW format.
		* b: Kernel can merge successive operations if the two chunk IDs
		* are contiguous. This can be problematic when there is a crash
		* during merge; specifically when the merge operation has dependency.
		* These dependencies can only happen during copy operations.
		*
		* To avoid this problem, we make sure that no two copy-operations
		* do not have contiguous chunk IDs. Additionally, we make sure
		* that each copy operation is merged individually.
		* 6: Use a monotonically increasing chunk number to assign the
		* new_chunk
		* 7: Each chunk-id represents either a: Metadata page or b: Data page
		* 8: Chunk-id representing a data page is stored in a vector. Index is the
		* chunk-id and value is the pointer to the CowOperation
		* 8: Chunk-id representing a data page is stored in a map.
		* 9: Chunk-id representing a metadata page is converted into a vector
		* index. We store this in vector as kernel requests metadata during
		* two stage:
		@@ -327,7 +361,10 @@ int Snapuserd::ReadDiskExceptions(chunk_t chunk, size_t read_size) {
		int Snapuserd::ReadMetadata() {
		reader_ = std::make_unique<CowReader>();
		CowHeader header;
		CowFooter footer;
		CowOptions options;
		bool prev_copy_op = false;

		LOG(DEBUG) << "ReadMetadata Start...";

		if (!reader_->Parse(cow_fd_)) {
		LOG(ERROR) << "Failed to parse";
		@@ -339,48 +376,33 @@ int Snapuserd::ReadMetadata() {
		return 1;
		}

		if (!reader_->GetFooter(&footer)) {
		LOG(ERROR) << "Failed to get footer";
		return 1;
		}

		CHECK(header.block_size == BLOCK_SIZE);

		LOG(DEBUG) << "Num-ops: " << std::hex << footer.op.num_ops;
		LOG(DEBUG) << "ops-size: " << std::hex << footer.op.ops_size;

		cowop_iter_ = reader_->GetOpIter();

		if (cowop_iter_ == nullptr) {
		LOG(ERROR) << "Failed to get cowop_iter";
		return 1;
		}
		cowop_riter_ = reader_->GetRevOpIter();

		exceptions_per_area_ = (CHUNK_SIZE << SECTOR_SHIFT) / sizeof(struct disk_exception);

		// Start from chunk number 2. Chunk 0 represents header and chunk 1
		// represents first metadata page.
		chunk_t next_free = NUM_SNAPSHOT_HDR_CHUNKS + 1;
		chunk_vec_.push_back(nullptr);
		chunk_vec_.push_back(nullptr);

		loff_t offset = 0;
		std::unique_ptr<uint8_t[]> de_ptr =
		std::make_unique<uint8_t[]>(exceptions_per_area_ * sizeof(struct disk_exception));

		// This memset is important. Kernel will stop issuing IO when new-chunk ID
		// is 0. When Area is not filled completely will all 256 exceptions,
		// is 0. When Area is not filled completely with all 256 exceptions,
		// this memset will ensure that metadata read is completed.
		memset(de_ptr.get(), 0, (exceptions_per_area_ * sizeof(struct disk_exception)));
		size_t num_ops = 0;

		while (!cowop_iter_->Done()) {
		const CowOperation* cow_op = &cowop_iter_->Get();
		while (!cowop_riter_->Done()) {
		const CowOperation* cow_op = &cowop_riter_->Get();
		struct disk_exception* de =
		reinterpret_cast<struct disk_exception>((char)de_ptr.get() + offset);

		if (cow_op->type == kCowFooterOp \|\| cow_op->type == kCowLabelOp) {
		cowop_iter_->Next();
		cowop_riter_->Next();
		continue;
		}

		@@ -390,61 +412,52 @@ int Snapuserd::ReadMetadata() {
		return 1;
		}

		if ((cow_op->type == kCowCopyOp \|\| prev_copy_op)) {
		next_free = GetNextAllocatableChunkId(next_free);
		}

		prev_copy_op = (cow_op->type == kCowCopyOp);

		// Construct the disk-exception
		de->old_chunk = cow_op->new_block;
		de->new_chunk = next_free;

		LOG(DEBUG) << "Old-chunk: " << de->old_chunk << "New-chunk: " << de->new_chunk;

		// Store operation pointer. Note, new-chunk ID is the index
		chunk_vec_.push_back(cow_op);
		CHECK(next_free == (chunk_vec_.size() - 1));
		// Store operation pointer.
		chunk_map_[next_free] = cow_op;
		num_ops += 1;

		offset += sizeof(struct disk_exception);

		cowop_iter_->Next();
		cowop_riter_->Next();

		// Find the next free chunk-id to be assigned. Check if the next free
		// chunk-id represents a metadata page. If so, skip it.
		next_free += 1;
		uint32_t stride = exceptions_per_area_ + 1;
		lldiv_t divresult = lldiv(next_free, stride);
		num_ops += 1;

		if (divresult.rem == NUM_SNAPSHOT_HDR_CHUNKS) {
		CHECK(num_ops == exceptions_per_area_);
		if (num_ops == exceptions_per_area_) {
		// Store it in vector at the right index. This maps the chunk-id to
		// vector index.
		vec_.push_back(std::move(de_ptr));
		offset = 0;
		num_ops = 0;

		chunk_t metadata_chunk = (next_free - exceptions_per_area_ - NUM_SNAPSHOT_HDR_CHUNKS);

		LOG(DEBUG) << "Area: " << vec_.size() - 1;
		LOG(DEBUG) << "Metadata-chunk: " << metadata_chunk;
		LOG(DEBUG) << "Sector number of Metadata-chunk: " << (metadata_chunk << CHUNK_SHIFT);

		// Create buffer for next area
		de_ptr = std::make_unique<uint8_t[]>(exceptions_per_area_ *
		sizeof(struct disk_exception));
		memset(de_ptr.get(), 0, (exceptions_per_area_ * sizeof(struct disk_exception)));

		// Since this is a metadata, store at this index
		chunk_vec_.push_back(nullptr);

		// Find the next free chunk-id
		next_free += 1;
		if (cowop_iter_->Done()) {
		if (cowop_riter_->Done()) {
		vec_.push_back(std::move(de_ptr));
		LOG(DEBUG) << "ReadMetadata() completed; Number of Areas: " << vec_.size();
		}
		}

		next_free = GetNextAllocatableChunkId(next_free);
		}

		// Partially filled area
		if (num_ops) {
		LOG(DEBUG) << "Partially filled area num_ops: " << num_ops;
		vec_.push_back(std::move(de_ptr));
		LOG(DEBUG) << "ReadMetadata() completed. Partially filled area num_ops: " << num_ops
		<< "Areas : " << vec_.size();
		}

		return 0;
		@@ -569,13 +582,7 @@ int Snapuserd::Run() {
		// vector, then it points to a metadata page.
		chunk_t chunk = (header->sector >> CHUNK_SHIFT);

		if (chunk >= chunk_vec_.size()) {
		ret = ZerofillDiskExceptions(read_size);
		if (ret < 0) {
		LOG(ERROR) << "ZerofillDiskExceptions failed";
		return ret;
		}
		} else if (chunk_vec_[chunk] == nullptr) {
		if (chunk_map_.find(chunk) == chunk_map_.end()) {
		ret = ReadDiskExceptions(chunk, read_size);
		if (ret < 0) {
		LOG(ERROR) << "ReadDiskExceptions failed";