1 // Copyright 2022 The Chromium Authors
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/memory/platform_shared_memory_mapper.h"
6
7 #include "base/logging.h"
8 #include "base/numerics/safe_conversions.h"
9
10 #include <sys/mman.h>
11
12 namespace base {
13
Map(subtle::PlatformSharedMemoryHandle handle,bool write_allowed,uint64_t offset,size_t size)14 std::optional<span<uint8_t>> PlatformSharedMemoryMapper::Map(
15 subtle::PlatformSharedMemoryHandle handle,
16 bool write_allowed,
17 uint64_t offset,
18 size_t size) {
19 // IMPORTANT: Even if the mapping is readonly and the mapped data is not
20 // changing, the region must ALWAYS be mapped with MAP_SHARED, otherwise with
21 // ashmem the mapping is equivalent to a private anonymous mapping.
22 void* address =
23 mmap(nullptr, size, PROT_READ | (write_allowed ? PROT_WRITE : 0),
24 MAP_SHARED, handle, checked_cast<off_t>(offset));
25
26 if (address == MAP_FAILED) {
27 DPLOG(ERROR) << "mmap " << handle << " failed";
28 return std::nullopt;
29 }
30
31 return make_span(static_cast<uint8_t*>(address), size);
32 }
33
Unmap(span<uint8_t> mapping)34 void PlatformSharedMemoryMapper::Unmap(span<uint8_t> mapping) {
35 if (munmap(mapping.data(), mapping.size()) < 0)
36 DPLOG(ERROR) << "munmap";
37 }
38
39 } // namespace base
40