base/files/memory_mapped_file_posix.cc

   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 #include "base/files/memory_mapped_file.h"
   6
   7 #include <sys/mman.h>
   8 #include <sys/stat.h>
   9 #include <unistd.h>
  10
  11 #include "base/logging.h"
  12 #include "base/threading/thread_restrictions.h"
  13
  14 namespace base {
  15
  16 MemoryMappedFile::MemoryMappedFile() : data_(NULL), length_(0) {
  17 }
  18
  19 bool MemoryMappedFile::MapFileRegionToMemory(
  20     const MemoryMappedFile::Region& region) {
  21   ThreadRestrictions::AssertIOAllowed();
  22
  23   off_t map_start = 0;
  24   size_t map_size = 0;
  25   int32 data_offset = 0;
  26
  27   if (region == MemoryMappedFile::Region::kWholeFile) {
  28     int64 file_len = file_.GetLength();
  29     if (file_len == -1) {
  30       DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
  31       return false;
  32     }
  33     map_size = static_cast<size_t>(file_len);
  34     length_ = map_size;
  35   } else {
  36     // The region can be arbitrarily aligned. mmap, instead, requires both the
  37     // start and size to be page-aligned. Hence, we map here the page-aligned
  38     // outer region [|aligned_start|, |aligned_start| + |size|] which contains
  39     // |region| and then add up the |data_offset| displacement.
  40     int64 aligned_start = 0;
  41     int64 aligned_size = 0;
  42     CalculateVMAlignedBoundaries(region.offset,
  43                                  region.size,
  44                                  &aligned_start,
  45                                  &aligned_size,
  46                                  &data_offset);
  47
  48     // Ensure that the casts in the mmap call below are sane.
  49     if (aligned_start < 0 || aligned_size < 0 ||
  50         aligned_start > std::numeric_limits<off_t>::max() ||
  51         static_cast<uint64>(aligned_size) >
  52             std::numeric_limits<size_t>::max() ||
  53         static_cast<uint64>(region.size) > std::numeric_limits<size_t>::max()) {
  54       DLOG(ERROR) << "Region bounds are not valid for mmap";
  55       return false;
  56     }
  57
  58     map_start = static_cast<off_t>(aligned_start);
  59     map_size = static_cast<size_t>(aligned_size);
  60     length_ = static_cast<size_t>(region.size);
  61   }
  62
  63   data_ = static_cast<uint8*>(mmap(NULL,
  64                                    map_size,
  65                                    PROT_READ,
  66                                    MAP_SHARED,
  67                                    file_.GetPlatformFile(),
  68                                    map_start));
  69   if (data_ == MAP_FAILED) {
  70     DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
  71     return false;
  72   }
  73
  74   data_ += data_offset;
  75   return true;
  76 }
  77
  78 void MemoryMappedFile::CloseHandles() {
  79   ThreadRestrictions::AssertIOAllowed();
  80
  81   if (data_ != NULL)
  82     munmap(data_, length_);
  83   file_.Close();
  84
  85   data_ = NULL;
  86   length_ = 0;
  87 }
  88
  89 }  // namespace base