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     bool operator==(const Region& other) const;
  32     bool operator!=(const Region& other) const;
  33
  34     // Start of the region (measured in bytes from the beginning of the file).
  35     int64 offset;
  36
  37     // Length of the region in bytes.
  38     int64 size;
  39   };
  40
  41   // Opens an existing file and maps it into memory. Access is restricted to
  42   // read only. If this object already points to a valid memory mapped file
  43   // then this method will fail and return false. If it cannot open the file,
  44   // the file does not exist, or the memory mapping fails, it will return false.
  45   // Later we may want to allow the user to specify access.
  46   bool Initialize(const FilePath& file_name);
  47
  48   // As above, but works with an already-opened file. MemoryMappedFile takes
  49   // ownership of |file| and closes it when done.
  50   bool Initialize(File file);
  51
  52   // As above, but works with a region of an already-opened file.
  53   bool Initialize(File file, const Region& region);
  54
  55 #if defined(OS_WIN)
  56   // Opens an existing file and maps it as an image section. Please refer to
  57   // the Initialize function above for additional information.
  58   bool InitializeAsImageSection(const FilePath& file_name);
  59 #endif  // OS_WIN
  60
  61   const uint8* data() const { return data_; }
  62   size_t length() const { return length_; }
  63
  64   // Is file_ a valid file handle that points to an open, memory mapped file?
  65   bool IsValid() const;
  66
  67  private:
  68   // Given the arbitrarily aligned memory region [start, size], returns the
  69   // boundaries of the region aligned to the granularity specified by the OS,
  70   // (a page on Linux, ~32k on Windows) as follows:
  71   // - |aligned_start| is page aligned and <= |start|.
  72   // - |aligned_size| is a multiple of the VM granularity and >= |size|.
  73   // - |offset| is the displacement of |start| w.r.t |aligned_start|.
  74   static void CalculateVMAlignedBoundaries(int64 start,
  75                                            int64 size,
  76                                            int64* aligned_start,
  77                                            int64* aligned_size,
  78                                            int32* offset);
  79
  80   // Map the file to memory, set data_ to that memory address. Return true on
  81   // success, false on any kind of failure. This is a helper for Initialize().
  82   bool MapFileRegionToMemory(const Region& region);
  83
  84   // Closes all open handles.
  85   void CloseHandles();
  86
  87   File file_;
  88   uint8* data_;
  89   size_t length_;
  90
  91 #if defined(OS_WIN)
  92   win::ScopedHandle file_mapping_;
  93   bool image_;  // Map as an image.
  94 #endif
  95
  96   DISALLOW_COPY_AND_ASSIGN(MemoryMappedFile);
  97 };
  98
  99 }  // namespace base
 100
 101 #endif  // BASE_FILES_MEMORY_MAPPED_FILE_H_