| // Copyright 2015 The Chromium OS Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef _BSDIFF_EXTENTS_FILE_H_ |
| #define _BSDIFF_EXTENTS_FILE_H_ |
| |
| #include <stddef.h> |
| #include <stdint.h> |
| |
| #include <memory> |
| #include <vector> |
| |
| #include "bsdiff/file_interface.h" |
| |
| /* |
| * Extent files. |
| * |
| * This modules provides a familiar interface for handling files through an |
| * indirection layer of extents, which are contiguous chunks of variable length |
| * at arbitrary offsets within a file. Once an extent file handle is obtained, |
| * users may read, write and seek as they do with ordinary files, having the I/O |
| * with the underlying file done for them by the extent file implementation. The |
| * implementation supports "sparse extents", which are assumed to contain zeros |
| * but otherwise have no actual representation in the underlying file; these are |
| * denoted by negative offset values. |
| * |
| * Unlike ordinary files, the size of an extent file is fixed; it is not |
| * truncated on open, nor is writing past the extent span allowed. Also, writing |
| * to a sparse extent has no effect and will not raise an error. |
| */ |
| |
| namespace bsdiff { |
| |
| /* An extent, defined by an offset and a length. */ |
| struct BSDIFF_EXPORT ex_t { |
| off_t off; // the extent offset; negative indicates a sparse extent. |
| uint64_t len; // the extent length. |
| }; |
| |
| class BSDIFF_EXPORT ExtentsFile : public FileInterface { |
| public: |
| // Creates an ExtentsFile based on the underlying |file| passed. The positions |
| // in the ExtentsFile will be linearly mapped to the extents provided in |
| // |extents|. The created ExtentsFile takes ownership of the |file| will close |
| // it on destruction. |
| ExtentsFile(std::unique_ptr<FileInterface> file, |
| const std::vector<ex_t>& extents); |
| |
| ~ExtentsFile() override; |
| |
| // FileInterface overrides. |
| bool Read(void* buf, size_t count, size_t* bytes_read) override; |
| bool Write(const void* buf, size_t count, size_t* bytes_written) override; |
| bool Seek(off_t pos) override; |
| bool Close() override; |
| bool GetSize(uint64_t* size) override; |
| |
| private: |
| void AdvancePos(uint64_t size); |
| |
| // Performs an I/O operation (either read or write). This template shares the |
| // code for both Read() and Write() implementations. |
| template <typename T> |
| bool IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*), |
| T* buf, |
| size_t count, |
| size_t* bytes_processed); |
| |
| // The underlying FileInterace instance. |
| std::unique_ptr<FileInterface> file_; |
| |
| // The list of extents mapping this instance to |file_|. |
| const std::vector<ex_t> extents_; |
| |
| // The accumulated length of the extents. The i-th element contains the sum of |
| // the length of all the extents from 0 up to but not including the i-th |
| // extent. This reduces the complexity for random-access Seek() calls. |
| std::vector<uint64_t> acc_len_; |
| |
| // Current extent index. |
| size_t curr_ex_idx_{0}; |
| |
| // Current logical file position. |
| uint64_t curr_pos_{0}; |
| |
| // Total length of all extents (constant). |
| uint64_t total_ex_len_{0}; |
| }; |
| |
| } // namespace bsdiff |
| |
| #endif // _BSDIFF_EXTENTS_FILE_H_ |