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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 "base/base_export.h"
      9 #include "base/basictypes.h"
     10 #include "base/files/file.h"
     11 #include "build/build_config.h"
     12 
     13 #if defined(OS_WIN)
     14 #include <windows.h>
     15 #endif
     16 
     17 namespace base {
     18 
     19 class FilePath;
     20 
     21 class BASE_EXPORT MemoryMappedFile {
     22  public:
     23   // The default constructor sets all members to invalid/null values.
     24   MemoryMappedFile();
     25   ~MemoryMappedFile();
     26 
     27   // Used to hold information about a region [offset + size] of a file.
     28   struct BASE_EXPORT Region {
     29     static const Region kWholeFile;
     30 
     31     Region(int64 offset, int64 size);
     32 
     33     bool operator==(const Region& other) const;
     34 
     35     // Start of the region (measured in bytes from the beginning of the file).
     36     int64 offset;
     37 
     38     // Length of the region in bytes.
     39     int64 size;
     40 
     41    private:
     42     // This ctor is used only by kWholeFile, to construct a zero-sized Region
     43     // (which is forbidden by the public ctor) and uniquely identify kWholeFile.
     44     Region(base::LinkerInitialized);
     45   };
     46 
     47   // Opens an existing file and maps it into memory. Access is restricted to
     48   // read only. If this object already points to a valid memory mapped file
     49   // then this method will fail and return false. If it cannot open the file,
     50   // the file does not exist, or the memory mapping fails, it will return false.
     51   // Later we may want to allow the user to specify access.
     52   bool Initialize(const FilePath& file_name);
     53 
     54   // As above, but works with an already-opened file. MemoryMappedFile takes
     55   // ownership of |file| and closes it when done.
     56   bool Initialize(File file);
     57 
     58   // As above, but works with a region of an already-opened file.
     59   bool Initialize(File file, const Region& region);
     60 
     61 #if defined(OS_WIN)
     62   // Opens an existing file and maps it as an image section. Please refer to
     63   // the Initialize function above for additional information.
     64   bool InitializeAsImageSection(const FilePath& file_name);
     65 #endif  // OS_WIN
     66 
     67   const uint8* data() const { return data_; }
     68   size_t length() const { return length_; }
     69 
     70   // Is file_ a valid file handle that points to an open, memory mapped file?
     71   bool IsValid() const;
     72 
     73  private:
     74   // Given the arbitrarily aligned memory region [start, size], returns the
     75   // boundaries of the region aligned to the granularity specified by the OS,
     76   // (a page on Linux, ~32k on Windows) as follows:
     77   // - |aligned_start| is page aligned and <= |start|.
     78   // - |aligned_size| is a multiple of the VM granularity and >= |size|.
     79   // - |offset| is the displacement of |start| w.r.t |aligned_start|.
     80   static void CalculateVMAlignedBoundaries(int64 start,
     81                                            int64 size,
     82                                            int64* aligned_start,
     83                                            int64* aligned_size,
     84                                            int32* offset);
     85 
     86   // Map the file to memory, set data_ to that memory address. Return true on
     87   // success, false on any kind of failure. This is a helper for Initialize().
     88   bool MapFileRegionToMemory(const Region& region);
     89 
     90   // Closes all open handles.
     91   void CloseHandles();
     92 
     93   File file_;
     94   uint8* data_;
     95   size_t length_;
     96 
     97 #if defined(OS_WIN)
     98   win::ScopedHandle file_mapping_;
     99   bool image_;  // Map as an image.
    100 #endif
    101 
    102   DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
    103 };
    104 
    105 }  // namespace base
    106 
    107 #endif  // BASE_FILES_MEMORY_MAPPED_FILE_H_
    108