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      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   // The default constructor sets all members to invalid/null values.
     27   MemoryMappedFile();
     28   ~MemoryMappedFile();
     29 
     30   // Used to hold information about a region [offset + size] of a file.
     31   struct BASE_EXPORT Region {
     32     static const Region kWholeFile;
     33 
     34     bool operator==(const Region& other) const;
     35     bool operator!=(const Region& other) const;
     36 
     37     // Start of the region (measured in bytes from the beginning of the file).
     38     int64_t offset;
     39 
     40     // Length of the region in bytes.
     41     int64_t size;
     42   };
     43 
     44   // Opens an existing file and maps it into memory. Access is restricted to
     45   // read only. If this object already points to a valid memory mapped file
     46   // then this method will fail and return false. If it cannot open the file,
     47   // the file does not exist, or the memory mapping fails, it will return false.
     48   // Later we may want to allow the user to specify access.
     49   bool Initialize(const FilePath& file_name);
     50 
     51   // As above, but works with an already-opened file. MemoryMappedFile takes
     52   // ownership of |file| and closes it when done.
     53   bool Initialize(File file);
     54 
     55   // As above, but works with a region of an already-opened file.
     56   bool Initialize(File file, const Region& region);
     57 
     58 #if defined(OS_WIN)
     59   // Opens an existing file and maps it as an image section. Please refer to
     60   // the Initialize function above for additional information.
     61   bool InitializeAsImageSection(const FilePath& file_name);
     62 #endif  // OS_WIN
     63 
     64   const uint8_t* data() const { return data_; }
     65   size_t length() const { return length_; }
     66 
     67   // Is file_ a valid file handle that points to an open, memory mapped file?
     68   bool IsValid() const;
     69 
     70  private:
     71   // Given the arbitrarily aligned memory region [start, size], returns the
     72   // boundaries of the region aligned to the granularity specified by the OS,
     73   // (a page on Linux, ~32k on Windows) as follows:
     74   // - |aligned_start| is page aligned and <= |start|.
     75   // - |aligned_size| is a multiple of the VM granularity and >= |size|.
     76   // - |offset| is the displacement of |start| w.r.t |aligned_start|.
     77   static void CalculateVMAlignedBoundaries(int64_t start,
     78                                            int64_t size,
     79                                            int64_t* aligned_start,
     80                                            int64_t* aligned_size,
     81                                            int32_t* offset);
     82 
     83   // Map the file to memory, set data_ to that memory address. Return true on
     84   // success, false on any kind of failure. This is a helper for Initialize().
     85   bool MapFileRegionToMemory(const Region& region);
     86 
     87   // Closes all open handles.
     88   void CloseHandles();
     89 
     90   File file_;
     91   uint8_t* data_;
     92   size_t length_;
     93 
     94 #if defined(OS_WIN)
     95   win::ScopedHandle file_mapping_;
     96   bool image_;  // Map as an image.
     97 #endif
     98 
     99   DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
    100 };
    101 
    102 }  // namespace base
    103 
    104 #endif  // BASE_FILES_MEMORY_MAPPED_FILE_H_
    105