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 <fcntl.h>
8 #include <stddef.h>
9 #include <stdint.h>
10 #include <sys/mman.h>
11 #include <sys/stat.h>
12 #include <unistd.h>
13
14 #include "base/logging.h"
15 #include "base/numerics/safe_conversions.h"
16 #include "base/threading/thread_restrictions.h"
17 #include "build/build_config.h"
18
19 #if defined(OS_ANDROID)
20 #include <android/api-level.h>
21 #endif
22
23 namespace base {
24
MemoryMappedFile()25 MemoryMappedFile::MemoryMappedFile() : data_(nullptr), length_(0) {}
26
27 #if !defined(OS_NACL)
MapFileRegionToMemory(const MemoryMappedFile::Region & region,Access access)28 bool MemoryMappedFile::MapFileRegionToMemory(
29 const MemoryMappedFile::Region& region,
30 Access access) {
31 AssertBlockingAllowed();
32
33 off_t map_start = 0;
34 size_t map_size = 0;
35 int32_t data_offset = 0;
36
37 if (region == MemoryMappedFile::Region::kWholeFile) {
38 int64_t file_len = file_.GetLength();
39 if (file_len < 0) {
40 DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
41 return false;
42 }
43 if (!IsValueInRangeForNumericType<size_t>(file_len))
44 return false;
45 map_size = static_cast<size_t>(file_len);
46 length_ = map_size;
47 } else {
48 // The region can be arbitrarily aligned. mmap, instead, requires both the
49 // start and size to be page-aligned. Hence, we map here the page-aligned
50 // outer region [|aligned_start|, |aligned_start| + |size|] which contains
51 // |region| and then add up the |data_offset| displacement.
52 int64_t aligned_start = 0;
53 size_t aligned_size = 0;
54 CalculateVMAlignedBoundaries(region.offset,
55 region.size,
56 &aligned_start,
57 &aligned_size,
58 &data_offset);
59
60 // Ensure that the casts in the mmap call below are sane.
61 if (aligned_start < 0 ||
62 !IsValueInRangeForNumericType<off_t>(aligned_start)) {
63 DLOG(ERROR) << "Region bounds are not valid for mmap";
64 return false;
65 }
66
67 map_start = static_cast<off_t>(aligned_start);
68 map_size = aligned_size;
69 length_ = region.size;
70 }
71
72 int flags = 0;
73 switch (access) {
74 case READ_ONLY:
75 flags |= PROT_READ;
76 break;
77
78 case READ_WRITE:
79 flags |= PROT_READ | PROT_WRITE;
80 break;
81
82 case READ_WRITE_EXTEND:
83 flags |= PROT_READ | PROT_WRITE;
84
85 const int64_t new_file_len = region.offset + region.size;
86
87 // POSIX won't auto-extend the file when it is written so it must first
88 // be explicitly extended to the maximum size. Zeros will fill the new
89 // space. It is assumed that the existing file is fully realized as
90 // otherwise the entire file would have to be read and possibly written.
91 const int64_t original_file_len = file_.GetLength();
92 if (original_file_len < 0) {
93 DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
94 return false;
95 }
96
97 // Increase the actual length of the file, if necessary. This can fail if
98 // the disk is full and the OS doesn't support sparse files.
99 if (!file_.SetLength(std::max(original_file_len, new_file_len))) {
100 DPLOG(ERROR) << "ftruncate " << file_.GetPlatformFile();
101 return false;
102 }
103
104 // Realize the extent of the file so that it can't fail (and crash) later
105 // when trying to write to a memory page that can't be created. This can
106 // fail if the disk is full and the file is sparse.
107 bool do_manual_extension = false;
108
109 #if defined(OS_ANDROID) && __ANDROID_API__ < 21
110 // Only Android API>=21 supports the fallocate call. Older versions need
111 // to manually extend the file by writing zeros at block intervals.
112 do_manual_extension = true;
113 #elif defined(OS_MACOSX)
114 // MacOS doesn't support fallocate even though their new APFS filesystem
115 // does support sparse files. It does, however, have the functionality
116 // available via fcntl.
117 // See also: https://openradar.appspot.com/32720223
118 fstore_t params = {F_ALLOCATEALL, F_PEOFPOSMODE, region.offset,
119 region.size, 0};
120 if (fcntl(file_.GetPlatformFile(), F_PREALLOCATE, ¶ms) != 0) {
121 DPLOG(ERROR) << "F_PREALLOCATE";
122 // This can fail because the filesystem doesn't support it so don't
123 // give up just yet. Try the manual method below.
124 do_manual_extension = true;
125 }
126 #else
127 if (posix_fallocate(file_.GetPlatformFile(), region.offset,
128 region.size) != 0) {
129 DPLOG(ERROR) << "posix_fallocate";
130 // This can fail because the filesystem doesn't support it so don't
131 // give up just yet. Try the manual method below.
132 do_manual_extension = true;
133 }
134 #endif
135
136 // Manually realize the extended file by writing bytes to it at intervals.
137 if (do_manual_extension) {
138 int64_t block_size = 512; // Start with something safe.
139 struct stat statbuf;
140 if (fstat(file_.GetPlatformFile(), &statbuf) == 0 &&
141 statbuf.st_blksize > 0) {
142 block_size = statbuf.st_blksize;
143 }
144
145 // Write starting at the next block boundary after the old file length.
146 const int64_t extension_start =
147 (original_file_len + block_size - 1) & ~(block_size - 1);
148 for (int64_t i = extension_start; i < new_file_len; i += block_size) {
149 char existing_byte;
150 if (pread(file_.GetPlatformFile(), &existing_byte, 1, i) != 1)
151 return false; // Can't read? Not viable.
152 if (existing_byte != 0)
153 continue; // Block has data so must already exist.
154 if (pwrite(file_.GetPlatformFile(), &existing_byte, 1, i) != 1)
155 return false; // Can't write? Not viable.
156 }
157 }
158
159 break;
160 }
161
162 data_ = static_cast<uint8_t*>(mmap(nullptr, map_size, flags, MAP_SHARED,
163 file_.GetPlatformFile(), map_start));
164 if (data_ == MAP_FAILED) {
165 DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
166 return false;
167 }
168
169 data_ += data_offset;
170 return true;
171 }
172 #endif
173
CloseHandles()174 void MemoryMappedFile::CloseHandles() {
175 AssertBlockingAllowed();
176
177 if (data_ != nullptr)
178 munmap(data_, length_);
179 file_.Close();
180
181 data_ = nullptr;
182 length_ = 0;
183 }
184
185 } // namespace base
186