// Copyright 2013 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#include "base/files/memory_mapped_file.h"
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#include <fcntl.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include "base/logging.h"
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#include "base/numerics/safe_conversions.h"
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#include "base/threading/thread_restrictions.h"
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#include "build/build_config.h"
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#if defined(OS_ANDROID)
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#include <android/api-level.h>
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#endif
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namespace base {
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MemoryMappedFile::MemoryMappedFile() : data_(nullptr), length_(0) {}
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#if !defined(OS_NACL)
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bool MemoryMappedFile::MapFileRegionToMemory(
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const MemoryMappedFile::Region& region,
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Access access) {
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AssertBlockingAllowed();
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off_t map_start = 0;
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size_t map_size = 0;
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int32_t data_offset = 0;
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if (region == MemoryMappedFile::Region::kWholeFile) {
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int64_t file_len = file_.GetLength();
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if (file_len < 0) {
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DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
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return false;
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}
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if (!IsValueInRangeForNumericType<size_t>(file_len))
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return false;
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map_size = static_cast<size_t>(file_len);
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length_ = map_size;
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} else {
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// The region can be arbitrarily aligned. mmap, instead, requires both the
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// start and size to be page-aligned. Hence, we map here the page-aligned
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// outer region [|aligned_start|, |aligned_start| + |size|] which contains
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// |region| and then add up the |data_offset| displacement.
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int64_t aligned_start = 0;
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size_t aligned_size = 0;
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CalculateVMAlignedBoundaries(region.offset,
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region.size,
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&aligned_start,
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&aligned_size,
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&data_offset);
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// Ensure that the casts in the mmap call below are sane.
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if (aligned_start < 0 ||
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!IsValueInRangeForNumericType<off_t>(aligned_start)) {
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DLOG(ERROR) << "Region bounds are not valid for mmap";
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return false;
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}
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map_start = static_cast<off_t>(aligned_start);
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map_size = aligned_size;
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length_ = region.size;
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}
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int flags = 0;
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switch (access) {
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case READ_ONLY:
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flags |= PROT_READ;
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break;
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case READ_WRITE:
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flags |= PROT_READ | PROT_WRITE;
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break;
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case READ_WRITE_EXTEND:
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flags |= PROT_READ | PROT_WRITE;
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const int64_t new_file_len = region.offset + region.size;
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// POSIX won't auto-extend the file when it is written so it must first
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// be explicitly extended to the maximum size. Zeros will fill the new
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// space. It is assumed that the existing file is fully realized as
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// otherwise the entire file would have to be read and possibly written.
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const int64_t original_file_len = file_.GetLength();
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if (original_file_len < 0) {
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DPLOG(ERROR) << "fstat " << file_.GetPlatformFile();
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return false;
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}
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// Increase the actual length of the file, if necessary. This can fail if
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// the disk is full and the OS doesn't support sparse files.
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if (!file_.SetLength(std::max(original_file_len, new_file_len))) {
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DPLOG(ERROR) << "ftruncate " << file_.GetPlatformFile();
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return false;
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}
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// Realize the extent of the file so that it can't fail (and crash) later
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// when trying to write to a memory page that can't be created. This can
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// fail if the disk is full and the file is sparse.
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bool do_manual_extension = false;
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#if defined(OS_ANDROID) && __ANDROID_API__ < 21
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// Only Android API>=21 supports the fallocate call. Older versions need
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// to manually extend the file by writing zeros at block intervals.
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do_manual_extension = true;
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#elif defined(OS_MACOSX)
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// MacOS doesn't support fallocate even though their new APFS filesystem
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// does support sparse files. It does, however, have the functionality
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// available via fcntl.
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// See also: https://openradar.appspot.com/32720223
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fstore_t params = {F_ALLOCATEALL, F_PEOFPOSMODE, region.offset,
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region.size, 0};
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if (fcntl(file_.GetPlatformFile(), F_PREALLOCATE, ¶ms) != 0) {
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DPLOG(ERROR) << "F_PREALLOCATE";
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// This can fail because the filesystem doesn't support it so don't
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// give up just yet. Try the manual method below.
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do_manual_extension = true;
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}
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#else
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if (posix_fallocate(file_.GetPlatformFile(), region.offset,
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region.size) != 0) {
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DPLOG(ERROR) << "posix_fallocate";
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// This can fail because the filesystem doesn't support it so don't
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// give up just yet. Try the manual method below.
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do_manual_extension = true;
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}
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#endif
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// Manually realize the extended file by writing bytes to it at intervals.
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if (do_manual_extension) {
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int64_t block_size = 512; // Start with something safe.
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struct stat statbuf;
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if (fstat(file_.GetPlatformFile(), &statbuf) == 0 &&
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statbuf.st_blksize > 0) {
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block_size = statbuf.st_blksize;
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}
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// Write starting at the next block boundary after the old file length.
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const int64_t extension_start =
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(original_file_len + block_size - 1) & ~(block_size - 1);
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for (int64_t i = extension_start; i < new_file_len; i += block_size) {
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char existing_byte;
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if (pread(file_.GetPlatformFile(), &existing_byte, 1, i) != 1)
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return false; // Can't read? Not viable.
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if (existing_byte != 0)
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continue; // Block has data so must already exist.
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if (pwrite(file_.GetPlatformFile(), &existing_byte, 1, i) != 1)
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return false; // Can't write? Not viable.
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}
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}
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break;
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}
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data_ = static_cast<uint8_t*>(mmap(nullptr, map_size, flags, MAP_SHARED,
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file_.GetPlatformFile(), map_start));
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if (data_ == MAP_FAILED) {
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DPLOG(ERROR) << "mmap " << file_.GetPlatformFile();
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return false;
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}
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data_ += data_offset;
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return true;
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}
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#endif
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void MemoryMappedFile::CloseHandles() {
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AssertBlockingAllowed();
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if (data_ != nullptr)
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munmap(data_, length_);
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file_.Close();
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data_ = nullptr;
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length_ = 0;
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}
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} // namespace base
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