1 // Copyright 2015 The Chromium OS Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef _BSDIFF_EXTENTS_FILE_H_ 6 #define _BSDIFF_EXTENTS_FILE_H_ 7 8 #include <stdio.h> 9 10 #include <memory> 11 #include <vector> 12 13 #include "bsdiff/file_interface.h" 14 15 /* 16 * Extent files. 17 * 18 * This modules provides a familiar interface for handling files through an 19 * indirection layer of extents, which are contiguous chunks of variable length 20 * at arbitrary offsets within a file. Once an extent file handle is obtained, 21 * users may read, write and seek as they do with ordinary files, having the I/O 22 * with the underlying file done for them by the extent file implementation. The 23 * implementation supports "sparse extents", which are assumed to contain zeros 24 * but otherwise have no actual representation in the underlying file; these are 25 * denoted by negative offset values. 26 * 27 * Unlike ordinary files, the size of an extent file is fixed; it is not 28 * truncated on open, nor is writing past the extent span allowed. Also, writing 29 * to a sparse extent has no effect and will not raise an error. 30 */ 31 32 namespace bsdiff { 33 34 /* An extent, defined by an offset and a length. */ 35 struct ex_t { 36 off_t off; // the extent offset; negative indicates a sparse extent. 37 uint64_t len; // the extent length. 38 }; 39 40 class ExtentsFile : public FileInterface { 41 public: 42 // Creates an ExtentsFile based on the underlying |file| passed. The positions 43 // in the ExtentsFile will be linearly mapped to the extents provided in 44 // |extents|. The created ExtentsFile takes ownership of the |file| will close 45 // it on destruction. 46 ExtentsFile(std::unique_ptr<FileInterface> file, 47 const std::vector<ex_t>& extents); 48 49 ~ExtentsFile() override; 50 51 // FileInterface overrides. 52 bool Read(void* buf, size_t count, size_t* bytes_read) override; 53 bool Write(const void* buf, size_t count, size_t* bytes_written) override; 54 bool Seek(off_t pos) override; 55 bool Close() override; 56 bool GetSize(uint64_t* size) override; 57 58 private: 59 void AdvancePos(uint64_t size); 60 61 // Performs an I/O operation (either read or write). This template shares the 62 // code for both Read() and Write() implementations. 63 template <typename T> 64 bool IOOperation(bool (FileInterface::*io_op)(T*, size_t, size_t*), 65 T* buf, 66 size_t count, 67 size_t* bytes_processed); 68 69 // The underlying FileInterace instance. 70 std::unique_ptr<FileInterface> file_; 71 72 // The list of extents mapping this instance to |file_|. 73 const std::vector<ex_t> extents_; 74 75 // The accumulated length of the extents. The i-th element contains the sum of 76 // the length of all the extents from 0 up to but not including the i-th 77 // extent. This reduces the complexity for random-access Seek() calls. 78 std::vector<uint64_t> acc_len_; 79 80 // Current extent index. 81 size_t curr_ex_idx_{0}; 82 83 // Current logical file position. 84 uint64_t curr_pos_{0}; 85 86 // Total length of all extents (constant). 87 uint64_t total_ex_len_{0}; 88 }; 89 90 } // namespace bsdiff 91 92 #endif // _BSDIFF_EXTENTS_FILE_H_ 93