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 <stddef.h>
8 #include <stdint.h>
9 #include <sys/mman.h>
10 #include <sys/stat.h>
11 #include <unistd.h>
12
13 #include "base/logging.h"
14 #include "base/threading/thread_restrictions.h"
15 #include "build/build_config.h"
16
17 namespace base {
18
MemoryMappedFile()19 MemoryMappedFile::MemoryMappedFile() : data_(NULL), length_(0) {
20 }
21
22 #if !defined(OS_NACL)
MapFileRegionToMemory(const MemoryMappedFile::Region & region,Access access)23 bool MemoryMappedFile::MapFileRegionToMemory(
24 const MemoryMappedFile::Region& region,
25 Access access) {
26 ThreadRestrictions::AssertIOAllowed();
27
28 off_t map_start = 0;
29 size_t map_size = 0;
30 int32_t data_offset = 0;
31
32 if (region == MemoryMappedFile::Region::kWholeFile) {
33 int64_t file_len = file_.GetLength();
34 if (file_len == -1) {
35 DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
36 return false;
37 }
38 map_size = static_cast<size_t>(file_len);
39 length_ = map_size;
40 } else {
41 // The region can be arbitrarily aligned. mmap, instead, requires both the
42 // start and size to be page-aligned. Hence, we map here the page-aligned
43 // outer region [|aligned_start|, |aligned_start| + |size|] which contains
44 // |region| and then add up the |data_offset| displacement.
45 int64_t aligned_start = 0;
46 int64_t aligned_size = 0;
47 CalculateVMAlignedBoundaries(region.offset,
48 region.size,
49 &aligned_start,
50 &aligned_size,
51 &data_offset);
52
53 // Ensure that the casts in the mmap call below are sane.
54 if (aligned_start < 0 || aligned_size < 0 ||
55 aligned_start > std::numeric_limits<off_t>::max() ||
56 static_cast<uint64_t>(aligned_size) >
57 std::numeric_limits<size_t>::max() ||
58 static_cast<uint64_t>(region.size) >
59 std::numeric_limits<size_t>::max()) {
60 DLOG(ERROR) << "Region bounds are not valid for mmap";
61 return false;
62 }
63
64 map_start = static_cast<off_t>(aligned_start);
65 map_size = static_cast<size_t>(aligned_size);
66 length_ = static_cast<size_t>(region.size);
67 }
68
69 int flags = 0;
70 switch (access) {
71 case READ_ONLY:
72 flags |= PROT_READ;
73 break;
74 case READ_WRITE:
75 flags |= PROT_READ | PROT_WRITE;
76 break;
77 case READ_WRITE_EXTEND:
78 // POSIX won't auto-extend the file when it is written so it must first
79 // be explicitly extended to the maximum size. Zeros will fill the new
80 // space.
81 file_.SetLength(std::max(file_.GetLength(), region.offset + region.size));
82 flags |= PROT_READ | PROT_WRITE;
83 break;
84 }
85 data_ = static_cast<uint8_t*>(mmap(NULL, map_size, flags, MAP_SHARED,
86 file_.GetPlatformFile(), map_start));
87 if (data_ == MAP_FAILED) {
88 DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
89 return false;
90 }
91
92 data_ += data_offset;
93 return true;
94 }
95 #endif
96
CloseHandles()97 void MemoryMappedFile::CloseHandles() {
98 ThreadRestrictions::AssertIOAllowed();
99
100 if (data_ != NULL)
101 munmap(data_, length_);
102 file_.Close();
103
104 data_ = NULL;
105 length_ = 0;
106 }
107
108 } // namespace base
109