shared_memory_posix.cc revision a873c8ac8e3c7252f191b1774a9137a91b8ae80d 
1// Copyright (c) 2010 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/shared_memory.h"
6
7#include <errno.h>
8#include <fcntl.h>
9#include <sys/mman.h>
10#include <sys/stat.h>
11#include <unistd.h>
12
13#include "base/file_util.h"
14#include "base/logging.h"
15#include "base/threading/platform_thread.h"
16#include "base/safe_strerror_posix.h"
17#include "base/threading/thread_restrictions.h"
18#include "base/utf_string_conversions.h"
19
20namespace base {
21
22namespace {
23// Paranoia. Semaphores and shared memory segments should live in different
24// namespaces, but who knows what's out there.
25const char kSemaphoreSuffix[] = "-sem";
26}
27
28SharedMemory::SharedMemory()
29    : mapped_file_(-1),
30      mapped_size_(0),
31      inode_(0),
32      memory_(NULL),
33      read_only_(false),
34      created_size_(0) {
35}
36
37SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only)
38    : mapped_file_(handle.fd),
39      mapped_size_(0),
40      inode_(0),
41      memory_(NULL),
42      read_only_(read_only),
43      created_size_(0) {
44  struct stat st;
45  if (fstat(handle.fd, &st) == 0) {
46    // If fstat fails, then the file descriptor is invalid and we'll learn this
47    // fact when Map() fails.
48    inode_ = st.st_ino;
49  }
50}
51
52SharedMemory::SharedMemory(SharedMemoryHandle handle, bool read_only,
53                           ProcessHandle process)
54    : mapped_file_(handle.fd),
55      mapped_size_(0),
56      inode_(0),
57      memory_(NULL),
58      read_only_(read_only),
59      created_size_(0) {
60  // We don't handle this case yet (note the ignored parameter); let's die if
61  // someone comes calling.
62  NOTREACHED();
63}
64
65SharedMemory::~SharedMemory() {
66  Close();
67}
68
69// static
70bool SharedMemory::IsHandleValid(const SharedMemoryHandle& handle) {
71  return handle.fd >= 0;
72}
73
74// static
75SharedMemoryHandle SharedMemory::NULLHandle() {
76  return SharedMemoryHandle();
77}
78
79// static
80void SharedMemory::CloseHandle(const SharedMemoryHandle& handle) {
81  DCHECK(handle.fd >= 0);
82  close(handle.fd);
83}
84
85bool SharedMemory::CreateAndMapAnonymous(uint32 size) {
86  return CreateAnonymous(size) && Map(size);
87}
88
89bool SharedMemory::CreateAnonymous(uint32 size) {
90  return CreateNamed("", false, size);
91}
92
93// Chromium mostly only uses the unique/private shmem as specified by
94// "name == L"". The exception is in the StatsTable.
95// TODO(jrg): there is no way to "clean up" all unused named shmem if
96// we restart from a crash.  (That isn't a new problem, but it is a problem.)
97// In case we want to delete it later, it may be useful to save the value
98// of mem_filename after FilePathForMemoryName().
99bool SharedMemory::CreateNamed(const std::string& name,
100                               bool open_existing, uint32 size) {
101  DCHECK(mapped_file_ == -1);
102  if (size == 0) return false;
103
104  // This function theoretically can block on the disk, but realistically
105  // the temporary files we create will just go into the buffer cache
106  // and be deleted before they ever make it out to disk.
107  base::ThreadRestrictions::ScopedAllowIO allow_io;
108
109  FILE *fp;
110  bool fix_size = true;
111
112  FilePath path;
113  if (name.empty()) {
114    // It doesn't make sense to have a open-existing private piece of shmem
115    DCHECK(!open_existing);
116    // Q: Why not use the shm_open() etc. APIs?
117    // A: Because they're limited to 4mb on OS X.  FFFFFFFUUUUUUUUUUU
118    fp = file_util::CreateAndOpenTemporaryShmemFile(&path);
119
120    // Deleting the file prevents anyone else from mapping it in
121    // (making it private), and prevents the need for cleanup (once
122    // the last fd is closed, it is truly freed).
123    if (fp)
124      file_util::Delete(path, false);
125
126  } else {
127    if (!FilePathForMemoryName(name, &path))
128      return false;
129
130    fp = file_util::OpenFile(path, "w+x");
131    if (fp == NULL && open_existing) {
132      // "w+" will truncate if it already exists.
133      fp = file_util::OpenFile(path, "a+");
134      fix_size = false;
135    }
136  }
137  if (fp && fix_size) {
138    // Get current size.
139    struct stat stat;
140    if (fstat(fileno(fp), &stat) != 0)
141      return false;
142    const uint32 current_size = stat.st_size;
143    if (current_size != size) {
144      if (ftruncate(fileno(fp), size) != 0)
145        return false;
146      if (fseeko(fp, size, SEEK_SET) != 0)
147        return false;
148    }
149    created_size_ = size;
150  }
151  if (fp == NULL) {
152#if !defined(OS_MACOSX)
153    PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
154    FilePath dir = path.DirName();
155    if (access(dir.value().c_str(), W_OK | X_OK) < 0) {
156      PLOG(ERROR) << "Unable to access(W_OK|X_OK) " << dir.value();
157      if (dir.value() == "/dev/shm") {
158        LOG(FATAL) << "This is frequently caused by incorrect permissions on "
159        << "/dev/shm.  Try 'sudo chmod 1777 /dev/shm' to fix.";
160      }
161    }
162#else
163    PLOG(ERROR) << "Creating shared memory in " << path.value() << " failed";
164#endif
165    return false;
166  }
167
168  return PrepareMapFile(fp);
169}
170
171// Our current implementation of shmem is with mmap()ing of files.
172// These files need to be deleted explicitly.
173// In practice this call is only needed for unit tests.
174bool SharedMemory::Delete(const std::string& name) {
175  FilePath path;
176  if (!FilePathForMemoryName(name, &path))
177    return false;
178
179  if (file_util::PathExists(path)) {
180    return file_util::Delete(path, false);
181  }
182
183  // Doesn't exist, so success.
184  return true;
185}
186
187bool SharedMemory::Open(const std::string& name, bool read_only) {
188  FilePath path;
189  if (!FilePathForMemoryName(name, &path))
190    return false;
191
192  read_only_ = read_only;
193
194  const char *mode = read_only ? "r" : "r+";
195  FILE *fp = file_util::OpenFile(path, mode);
196  return PrepareMapFile(fp);
197}
198
199bool SharedMemory::Map(uint32 bytes) {
200  if (mapped_file_ == -1)
201    return false;
202
203  memory_ = mmap(NULL, bytes, PROT_READ | (read_only_ ? 0 : PROT_WRITE),
204                 MAP_SHARED, mapped_file_, 0);
205
206  if (memory_)
207    mapped_size_ = bytes;
208
209  bool mmap_succeeded = (memory_ != (void*)-1);
210  DCHECK(mmap_succeeded) << "Call to mmap failed, errno=" << errno;
211  return mmap_succeeded;
212}
213
214bool SharedMemory::Unmap() {
215  if (memory_ == NULL)
216    return false;
217
218  munmap(memory_, mapped_size_);
219  memory_ = NULL;
220  mapped_size_ = 0;
221  return true;
222}
223
224SharedMemoryHandle SharedMemory::handle() const {
225  return FileDescriptor(mapped_file_, false);
226}
227
228void SharedMemory::Close() {
229  Unmap();
230
231  if (mapped_file_ > 0) {
232    close(mapped_file_);
233    mapped_file_ = -1;
234  }
235}
236
237void SharedMemory::Lock() {
238#if !defined(ANDROID)
239  LockOrUnlockCommon(F_LOCK);
240#endif
241}
242
243void SharedMemory::Unlock() {
244#if !defined(ANDROID)
245  LockOrUnlockCommon(F_ULOCK);
246#endif
247}
248
249bool SharedMemory::PrepareMapFile(FILE *fp) {
250  DCHECK(mapped_file_ == -1);
251  if (fp == NULL) return false;
252
253  // This function theoretically can block on the disk, but realistically
254  // the temporary files we create will just go into the buffer cache
255  // and be deleted before they ever make it out to disk.
256  base::ThreadRestrictions::ScopedAllowIO allow_io;
257
258  file_util::ScopedFILE file_closer(fp);
259
260  mapped_file_ = dup(fileno(fp));
261  if (mapped_file_ == -1) {
262    if (errno == EMFILE) {
263      LOG(WARNING) << "Shared memory creation failed; out of file descriptors";
264      return false;
265    } else {
266      NOTREACHED() << "Call to dup failed, errno=" << errno;
267    }
268  }
269
270  struct stat st;
271  if (fstat(mapped_file_, &st))
272    NOTREACHED();
273  inode_ = st.st_ino;
274
275  return true;
276}
277
278// For the given shmem named |mem_name|, return a filename to mmap()
279// (and possibly create).  Modifies |filename|.  Return false on
280// error, or true of we are happy.
281bool SharedMemory::FilePathForMemoryName(const std::string& mem_name,
282                                         FilePath* path) {
283  // mem_name will be used for a filename; make sure it doesn't
284  // contain anything which will confuse us.
285  DCHECK(mem_name.find('/') == std::string::npos);
286  DCHECK(mem_name.find('\0') == std::string::npos);
287
288  FilePath temp_dir;
289  if (!file_util::GetShmemTempDir(&temp_dir))
290    return false;
291
292  *path = temp_dir.AppendASCII("com.google.chrome.shmem." + mem_name);
293  return true;
294}
295
296void SharedMemory::LockOrUnlockCommon(int function) {
297  DCHECK(mapped_file_ >= 0);
298#if !defined(ANDROID)
299  while (lockf(mapped_file_, function, 0) < 0) {
300    if (errno == EINTR) {
301      continue;
302    } else if (errno == ENOLCK) {
303      // temporary kernel resource exaustion
304      base::PlatformThread::Sleep(500);
305      continue;
306    } else {
307      NOTREACHED() << "lockf() failed."
308                   << " function:" << function
309                   << " fd:" << mapped_file_
310                   << " errno:" << errno
311                   << " msg:" << safe_strerror(errno);
312    }
313  }
314#endif
315}
316
317bool SharedMemory::ShareToProcessCommon(ProcessHandle process,
318                                        SharedMemoryHandle *new_handle,
319                                        bool close_self) {
320  const int new_fd = dup(mapped_file_);
321  DCHECK(new_fd >= 0);
322  new_handle->fd = new_fd;
323  new_handle->auto_close = true;
324
325  if (close_self)
326    Close();
327
328  return true;
329}
330
331}  // namespace base
332