1 // Copyright 2013 The Chromium 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 BASE_FILES_MEMORY_MAPPED_FILE_H_ 6 #define BASE_FILES_MEMORY_MAPPED_FILE_H_ 7 8 #include <stddef.h> 9 #include <stdint.h> 10 11 #include "base/base_export.h" 12 #include "base/files/file.h" 13 #include "base/macros.h" 14 #include "build/build_config.h" 15 16 #if defined(OS_WIN) 17 #include <windows.h> 18 #endif 19 20 namespace base { 21 22 class FilePath; 23 24 class BASE_EXPORT MemoryMappedFile { 25 public: 26 enum Access { 27 // Mapping a file into memory effectively allows for file I/O on any thread. 28 // The accessing thread could be paused while data from the file is paged 29 // into memory. Worse, a corrupted filesystem could cause a SEGV within the 30 // program instead of just an I/O error. 31 READ_ONLY, 32 33 // This provides read/write access to a file and must be used with care of 34 // the additional subtleties involved in doing so. Though the OS will do 35 // the writing of data on its own time, too many dirty pages can cause 36 // the OS to pause the thread while it writes them out. The pause can 37 // be as much as 1s on some systems. 38 READ_WRITE, 39 40 // This provides read/write access but with the ability to write beyond 41 // the end of the existing file up to a maximum size specified as the 42 // "region". Depending on the OS, the file may or may not be immediately 43 // extended to the maximum size though it won't be loaded in RAM until 44 // needed. Note, however, that the maximum size will still be reserved 45 // in the process address space. 46 READ_WRITE_EXTEND, 47 }; 48 49 // The default constructor sets all members to invalid/null values. 50 MemoryMappedFile(); 51 ~MemoryMappedFile(); 52 53 // Used to hold information about a region [offset + size] of a file. 54 struct BASE_EXPORT Region { 55 static const Region kWholeFile; 56 57 bool operator==(const Region& other) const; 58 bool operator!=(const Region& other) const; 59 60 // Start of the region (measured in bytes from the beginning of the file). 61 int64_t offset; 62 63 // Length of the region in bytes. 64 int64_t size; 65 }; 66 67 // Opens an existing file and maps it into memory. |access| can be read-only 68 // or read/write but not read/write+extend. If this object already points 69 // to a valid memory mapped file then this method will fail and return 70 // false. If it cannot open the file, the file does not exist, or the 71 // memory mapping fails, it will return false. 72 bool Initialize(const FilePath& file_name, Access access); 73 bool Initialize(const FilePath& file_name) { 74 return Initialize(file_name, READ_ONLY); 75 } 76 77 // As above, but works with an already-opened file. |access| can be read-only 78 // or read/write but not read/write+extend. MemoryMappedFile takes ownership 79 // of |file| and closes it when done. |file| must have been opened with 80 // permissions suitable for |access|. If the memory mapping fails, it will 81 // return false. 82 bool Initialize(File file, Access access); 83 bool Initialize(File file) { 84 return Initialize(std::move(file), READ_ONLY); 85 } 86 87 // As above, but works with a region of an already-opened file. All forms of 88 // |access| are allowed. If READ_WRITE_EXTEND is specified then |region| 89 // provides the maximum size of the file. If the memory mapping fails, it 90 // return false. 91 bool Initialize(File file, const Region& region, Access access); 92 bool Initialize(File file, const Region& region) { 93 return Initialize(std::move(file), region, READ_ONLY); 94 } 95 96 const uint8_t* data() const { return data_; } 97 uint8_t* data() { return data_; } 98 size_t length() const { return length_; } 99 100 // Is file_ a valid file handle that points to an open, memory mapped file? 101 bool IsValid() const; 102 103 private: 104 // Given the arbitrarily aligned memory region [start, size], returns the 105 // boundaries of the region aligned to the granularity specified by the OS, 106 // (a page on Linux, ~32k on Windows) as follows: 107 // - |aligned_start| is page aligned and <= |start|. 108 // - |aligned_size| is a multiple of the VM granularity and >= |size|. 109 // - |offset| is the displacement of |start| w.r.t |aligned_start|. 110 static void CalculateVMAlignedBoundaries(int64_t start, 111 int64_t size, 112 int64_t* aligned_start, 113 int64_t* aligned_size, 114 int32_t* offset); 115 116 // Map the file to memory, set data_ to that memory address. Return true on 117 // success, false on any kind of failure. This is a helper for Initialize(). 118 bool MapFileRegionToMemory(const Region& region, Access access); 119 120 // Closes all open handles. 121 void CloseHandles(); 122 123 File file_; 124 uint8_t* data_; 125 size_t length_; 126 127 #if defined(OS_WIN) 128 win::ScopedHandle file_mapping_; 129 #endif 130 131 DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile); 132 }; 133 134 } // namespace base 135 136 #endif // BASE_FILES_MEMORY_MAPPED_FILE_H_ 137
