base/files/memory_mapped_file.h

   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_