1 // Copyright (c) 2011 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/memory/shared_memory.h"
6 
7 #include <stddef.h>
8 #include <sys/mman.h>
9 
10 #include "base/logging.h"
11 #include "third_party/ashmem/ashmem.h"
12 
13 namespace base {
14 
15 // For Android, we use ashmem to implement SharedMemory. ashmem_create_region
16 // will automatically pin the region. We never explicitly call pin/unpin. When
17 // all the file descriptors from different processes associated with the region
18 // are closed, the memory buffer will go away.
19 
Create(const SharedMemoryCreateOptions & options)20 bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
21   DCHECK(!shm_.IsValid());
22 
23   if (options.size > static_cast<size_t>(std::numeric_limits<int>::max()))
24     return false;
25 
26   // "name" is just a label in ashmem. It is visible in /proc/pid/maps.
27   int fd = ashmem_create_region(
28       options.name_deprecated ? options.name_deprecated->c_str() : "",
29       options.size);
30   shm_ = SharedMemoryHandle::ImportHandle(fd, options.size);
31   if (!shm_.IsValid()) {
32     DLOG(ERROR) << "Shared memory creation failed";
33     return false;
34   }
35 
36   int flags = PROT_READ | PROT_WRITE | (options.executable ? PROT_EXEC : 0);
37   int err = ashmem_set_prot_region(shm_.GetHandle(), flags);
38   if (err < 0) {
39     DLOG(ERROR) << "Error " << err << " when setting protection of ashmem";
40     return false;
41   }
42 
43   requested_size_ = options.size;
44 
45   return true;
46 }
47 
Delete(const std::string & name)48 bool SharedMemory::Delete(const std::string& name) {
49   // Like on Windows, this is intentionally returning true as ashmem will
50   // automatically releases the resource when all FDs on it are closed.
51   return true;
52 }
53 
Open(const std::string & name,bool read_only)54 bool SharedMemory::Open(const std::string& name, bool read_only) {
55   // ashmem doesn't support name mapping
56   NOTIMPLEMENTED();
57   return false;
58 }
59 
Close()60 void SharedMemory::Close() {
61   if (shm_.IsValid()) {
62     shm_.Close();
63     shm_ = SharedMemoryHandle();
64   }
65 }
66 
GetReadOnlyHandle() const67 SharedMemoryHandle SharedMemory::GetReadOnlyHandle() const {
68   // There are no read-only Ashmem descriptors on Android.
69   // Instead, the protection mask is a property of the region itself.
70   SharedMemoryHandle handle = shm_.Duplicate();
71   handle.SetReadOnly();
72   return handle;
73 }
74 
75 }  // namespace base
76