file_path_watcher_linux.cc revision 5821806d5e7f356e8fa4b058a389a808ea183019 
1// Copyright (c) 2012 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/file_path_watcher.h"
6
7#include <errno.h>
8#include <string.h>
9#include <sys/inotify.h>
10#include <sys/ioctl.h>
11#include <sys/select.h>
12#include <unistd.h>
13
14#include <algorithm>
15#include <set>
16#include <utility>
17#include <vector>
18
19#include "base/bind.h"
20#include "base/eintr_wrapper.h"
21#include "base/file_path.h"
22#include "base/file_util.h"
23#include "base/hash_tables.h"
24#include "base/lazy_instance.h"
25#include "base/location.h"
26#include "base/logging.h"
27#include "base/memory/scoped_ptr.h"
28#include "base/message_loop.h"
29#include "base/message_loop_proxy.h"
30#include "base/synchronization/lock.h"
31#include "base/threading/thread.h"
32
33namespace base {
34namespace files {
35
36namespace {
37
38class FilePathWatcherImpl;
39
40// Singleton to manage all inotify watches.
41// TODO(tony): It would be nice if this wasn't a singleton.
42// http://crbug.com/38174
43class InotifyReader {
44 public:
45  typedef int Watch;  // Watch descriptor used by AddWatch and RemoveWatch.
46  static const Watch kInvalidWatch = -1;
47
48  // Watch directory |path| for changes. |watcher| will be notified on each
49  // change. Returns kInvalidWatch on failure.
50  Watch AddWatch(const FilePath& path, FilePathWatcherImpl* watcher);
51
52  // Remove |watch|. Returns true on success.
53  bool RemoveWatch(Watch watch, FilePathWatcherImpl* watcher);
54
55  // Callback for InotifyReaderTask.
56  void OnInotifyEvent(const inotify_event* event);
57
58 private:
59  friend struct ::base::DefaultLazyInstanceTraits<InotifyReader>;
60
61  typedef std::set<FilePathWatcherImpl*> WatcherSet;
62
63  InotifyReader();
64  ~InotifyReader();
65
66  // We keep track of which delegates want to be notified on which watches.
67  base::hash_map<Watch, WatcherSet> watchers_;
68
69  // Lock to protect watchers_.
70  base::Lock lock_;
71
72  // Separate thread on which we run blocking read for inotify events.
73  base::Thread thread_;
74
75  // File descriptor returned by inotify_init.
76  const int inotify_fd_;
77
78  // Use self-pipe trick to unblock select during shutdown.
79  int shutdown_pipe_[2];
80
81  // Flag set to true when startup was successful.
82  bool valid_;
83
84  DISALLOW_COPY_AND_ASSIGN(InotifyReader);
85};
86
87class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
88                            public MessageLoop::DestructionObserver {
89 public:
90  FilePathWatcherImpl();
91
92  // Called for each event coming from the watch. |fired_watch| identifies the
93  // watch that fired, |child| indicates what has changed, and is relative to
94  // the currently watched path for |fired_watch|. The flag |created| is true if
95  // the object appears.
96  void OnFilePathChanged(InotifyReader::Watch fired_watch,
97                         const FilePath::StringType& child,
98                         bool created);
99
100  // Start watching |path| for changes and notify |delegate| on each change.
101  // Returns true if watch for |path| has been added successfully.
102  virtual bool Watch(const FilePath& path,
103                     FilePathWatcher::Delegate* delegate) OVERRIDE;
104
105  // Cancel the watch. This unregisters the instance with InotifyReader.
106  virtual void Cancel() OVERRIDE;
107
108  // Deletion of the FilePathWatcher will call Cancel() to dispose of this
109  // object in the right thread. This also observes destruction of the required
110  // cleanup thread, in case it quits before Cancel() is called.
111  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
112
113 protected:
114  virtual ~FilePathWatcherImpl() {}
115
116 private:
117  // Cleans up and stops observing the |message_loop_| thread.
118  virtual void CancelOnMessageLoopThread() OVERRIDE;
119
120  // Inotify watches are installed for all directory components of |target_|. A
121  // WatchEntry instance holds the watch descriptor for a component and the
122  // subdirectory for that identifies the next component. If a symbolic link
123  // is being watched, the target of the link is also kept.
124  struct WatchEntry {
125    WatchEntry(InotifyReader::Watch watch, const FilePath::StringType& subdir)
126        : watch_(watch),
127          subdir_(subdir) {}
128
129    InotifyReader::Watch watch_;
130    FilePath::StringType subdir_;
131    FilePath::StringType linkname_;
132  };
133  typedef std::vector<WatchEntry> WatchVector;
134
135  // Reconfigure to watch for the most specific parent directory of |target_|
136  // that exists. Updates |watched_path_|. Returns true on success.
137  bool UpdateWatches() WARN_UNUSED_RESULT;
138
139  // Delegate to notify upon changes.
140  scoped_refptr<FilePathWatcher::Delegate> delegate_;
141
142  // The file or directory we're supposed to watch.
143  FilePath target_;
144
145  // The vector of watches and next component names for all path components,
146  // starting at the root directory. The last entry corresponds to the watch for
147  // |target_| and always stores an empty next component name in |subdir_|.
148  WatchVector watches_;
149
150  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
151};
152
153void InotifyReaderCallback(InotifyReader* reader, int inotify_fd,
154                           int shutdown_fd) {
155  // Make sure the file descriptors are good for use with select().
156  CHECK_LE(0, inotify_fd);
157  CHECK_GT(FD_SETSIZE, inotify_fd);
158  CHECK_LE(0, shutdown_fd);
159  CHECK_GT(FD_SETSIZE, shutdown_fd);
160
161  while (true) {
162    fd_set rfds;
163    FD_ZERO(&rfds);
164    FD_SET(inotify_fd, &rfds);
165    FD_SET(shutdown_fd, &rfds);
166
167    // Wait until some inotify events are available.
168    int select_result =
169      HANDLE_EINTR(select(std::max(inotify_fd, shutdown_fd) + 1,
170                          &rfds, NULL, NULL, NULL));
171    if (select_result < 0) {
172      DPLOG(WARNING) << "select failed";
173      return;
174    }
175
176    if (FD_ISSET(shutdown_fd, &rfds))
177      return;
178
179    // Adjust buffer size to current event queue size.
180    int buffer_size;
181    int ioctl_result = HANDLE_EINTR(ioctl(inotify_fd, FIONREAD,
182                                          &buffer_size));
183
184    if (ioctl_result != 0) {
185      DPLOG(WARNING) << "ioctl failed";
186      return;
187    }
188
189    std::vector<char> buffer(buffer_size);
190
191    ssize_t bytes_read = HANDLE_EINTR(read(inotify_fd, &buffer[0],
192                                           buffer_size));
193
194    if (bytes_read < 0) {
195      DPLOG(WARNING) << "read from inotify fd failed";
196      return;
197    }
198
199    ssize_t i = 0;
200    while (i < bytes_read) {
201      inotify_event* event = reinterpret_cast<inotify_event*>(&buffer[i]);
202      size_t event_size = sizeof(inotify_event) + event->len;
203      DCHECK(i + event_size <= static_cast<size_t>(bytes_read));
204      reader->OnInotifyEvent(event);
205      i += event_size;
206    }
207  }
208}
209
210static base::LazyInstance<InotifyReader>::Leaky g_inotify_reader =
211    LAZY_INSTANCE_INITIALIZER;
212
213InotifyReader::InotifyReader()
214    : thread_("inotify_reader"),
215      inotify_fd_(inotify_init()),
216      valid_(false) {
217  shutdown_pipe_[0] = -1;
218  shutdown_pipe_[1] = -1;
219  if (inotify_fd_ >= 0 && pipe(shutdown_pipe_) == 0 && thread_.Start()) {
220    thread_.message_loop()->PostTask(
221        FROM_HERE, base::Bind(&InotifyReaderCallback, this, inotify_fd_,
222                              shutdown_pipe_[0]));
223    valid_ = true;
224  }
225}
226
227InotifyReader::~InotifyReader() {
228  if (valid_) {
229    // Write to the self-pipe so that the select call in InotifyReaderTask
230    // returns.
231    ssize_t ret = HANDLE_EINTR(write(shutdown_pipe_[1], "", 1));
232    DPCHECK(ret > 0);
233    DCHECK_EQ(ret, 1);
234    thread_.Stop();
235  }
236  if (inotify_fd_ >= 0)
237    close(inotify_fd_);
238  if (shutdown_pipe_[0] >= 0)
239    close(shutdown_pipe_[0]);
240  if (shutdown_pipe_[1] >= 0)
241    close(shutdown_pipe_[1]);
242}
243
244InotifyReader::Watch InotifyReader::AddWatch(
245    const FilePath& path, FilePathWatcherImpl* watcher) {
246  if (!valid_)
247    return kInvalidWatch;
248
249  base::AutoLock auto_lock(lock_);
250
251  Watch watch = inotify_add_watch(inotify_fd_, path.value().c_str(),
252                                  IN_CREATE | IN_DELETE |
253                                  IN_CLOSE_WRITE | IN_MOVE |
254                                  IN_ONLYDIR);
255
256  if (watch == kInvalidWatch)
257    return kInvalidWatch;
258
259  watchers_[watch].insert(watcher);
260
261  return watch;
262}
263
264bool InotifyReader::RemoveWatch(Watch watch,
265                                FilePathWatcherImpl* watcher) {
266  if (!valid_)
267    return false;
268
269  base::AutoLock auto_lock(lock_);
270
271  watchers_[watch].erase(watcher);
272
273  if (watchers_[watch].empty()) {
274    watchers_.erase(watch);
275    return (inotify_rm_watch(inotify_fd_, watch) == 0);
276  }
277
278  return true;
279}
280
281void InotifyReader::OnInotifyEvent(const inotify_event* event) {
282  if (event->mask & IN_IGNORED)
283    return;
284
285  FilePath::StringType child(event->len ? event->name : FILE_PATH_LITERAL(""));
286  base::AutoLock auto_lock(lock_);
287
288  for (WatcherSet::iterator watcher = watchers_[event->wd].begin();
289       watcher != watchers_[event->wd].end();
290       ++watcher) {
291    (*watcher)->OnFilePathChanged(event->wd,
292                                  child,
293                                  event->mask & (IN_CREATE | IN_MOVED_TO));
294  }
295}
296
297FilePathWatcherImpl::FilePathWatcherImpl()
298    : delegate_(NULL) {
299}
300
301void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
302                                            const FilePath::StringType& child,
303                                            bool created) {
304  if (!message_loop()->BelongsToCurrentThread()) {
305    // Switch to message_loop_ to access watches_ safely.
306    message_loop()->PostTask(FROM_HERE,
307        base::Bind(&FilePathWatcherImpl::OnFilePathChanged,
308                   this,
309                   fired_watch,
310                   child,
311                   created));
312    return;
313  }
314
315  DCHECK(MessageLoopForIO::current());
316
317  // Find the entry in |watches_| that corresponds to |fired_watch|.
318  WatchVector::const_iterator watch_entry(watches_.begin());
319  for ( ; watch_entry != watches_.end(); ++watch_entry) {
320    if (fired_watch == watch_entry->watch_) {
321      // Check whether a path component of |target_| changed.
322      bool change_on_target_path = child.empty() ||
323          ((child == watch_entry->subdir_) && watch_entry->linkname_.empty()) ||
324          (child == watch_entry->linkname_);
325
326      // Check whether the change references |target_| or a direct child.
327      DCHECK(watch_entry->subdir_.empty() ||
328          (watch_entry + 1) != watches_.end());
329      bool target_changed =
330          (watch_entry->subdir_.empty() && (child == watch_entry->linkname_)) ||
331          (watch_entry->subdir_.empty() && watch_entry->linkname_.empty()) ||
332          (watch_entry->subdir_ == child && (watch_entry + 1)->subdir_.empty());
333
334      // Update watches if a directory component of the |target_| path
335      // (dis)appears. Note that we don't add the additional restriction
336      // of checking the event mask to see if it is for a directory here
337      // as changes to symlinks on the target path will not have
338      // IN_ISDIR set in the event masks. As a result we may sometimes
339      // call UpdateWatches() unnecessarily.
340      if (change_on_target_path && !UpdateWatches()) {
341        delegate_->OnFilePathError(target_);
342        return;
343      }
344
345      // Report the following events:
346      //  - The target or a direct child of the target got changed (in case the
347      //    watched path refers to a directory).
348      //  - One of the parent directories got moved or deleted, since the target
349      //    disappears in this case.
350      //  - One of the parent directories appears. The event corresponding to
351      //    the target appearing might have been missed in this case, so
352      //    recheck.
353      if (target_changed ||
354          (change_on_target_path && !created) ||
355          (change_on_target_path && file_util::PathExists(target_))) {
356        delegate_->OnFilePathChanged(target_);
357        return;
358      }
359    }
360  }
361}
362
363bool FilePathWatcherImpl::Watch(const FilePath& path,
364                                FilePathWatcher::Delegate* delegate) {
365  DCHECK(target_.empty());
366  DCHECK(MessageLoopForIO::current());
367
368  set_message_loop(base::MessageLoopProxy::current());
369  delegate_ = delegate;
370  target_ = path;
371  MessageLoop::current()->AddDestructionObserver(this);
372
373  std::vector<FilePath::StringType> comps;
374  target_.GetComponents(&comps);
375  DCHECK(!comps.empty());
376  std::vector<FilePath::StringType>::const_iterator comp = comps.begin();
377  for (++comp; comp != comps.end(); ++comp)
378    watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch, *comp));
379
380  watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch,
381                                FilePath::StringType()));
382  return UpdateWatches();
383}
384
385void FilePathWatcherImpl::Cancel() {
386  if (!delegate_) {
387    // Watch was never called, or the |message_loop_| thread is already gone.
388    set_cancelled();
389    return;
390  }
391
392  // Switch to the message_loop_ if necessary so we can access |watches_|.
393  if (!message_loop()->BelongsToCurrentThread()) {
394    message_loop()->PostTask(FROM_HERE,
395                             base::Bind(&FilePathWatcher::CancelWatch,
396                                        make_scoped_refptr(this)));
397  } else {
398    CancelOnMessageLoopThread();
399  }
400}
401
402void FilePathWatcherImpl::CancelOnMessageLoopThread() {
403  if (!is_cancelled())
404    set_cancelled();
405
406  if (delegate_) {
407    MessageLoop::current()->RemoveDestructionObserver(this);
408    delegate_ = NULL;
409  }
410
411  for (WatchVector::iterator watch_entry(watches_.begin());
412       watch_entry != watches_.end(); ++watch_entry) {
413    if (watch_entry->watch_ != InotifyReader::kInvalidWatch)
414      g_inotify_reader.Get().RemoveWatch(watch_entry->watch_, this);
415  }
416  watches_.clear();
417  target_.clear();
418}
419
420void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
421  CancelOnMessageLoopThread();
422}
423
424bool FilePathWatcherImpl::UpdateWatches() {
425  // Ensure this runs on the |message_loop_| exclusively in order to avoid
426  // concurrency issues.
427  DCHECK(message_loop()->BelongsToCurrentThread());
428
429  // Walk the list of watches and update them as we go.
430  FilePath path(FILE_PATH_LITERAL("/"));
431  bool path_valid = true;
432  for (WatchVector::iterator watch_entry(watches_.begin());
433       watch_entry != watches_.end(); ++watch_entry) {
434    InotifyReader::Watch old_watch = watch_entry->watch_;
435    if (path_valid) {
436      watch_entry->watch_ = g_inotify_reader.Get().AddWatch(path, this);
437      if ((watch_entry->watch_ == InotifyReader::kInvalidWatch) &&
438          file_util::IsLink(path)) {
439        FilePath link;
440        if (file_util::ReadSymbolicLink(path, &link)) {
441          if (!link.IsAbsolute())
442            link = path.DirName().Append(link);
443          // Try watching symlink target directory. If the link target is "/",
444          // then we shouldn't get here in normal situations and if we do, we'd
445          // watch "/" for changes to a component "/" which is harmless so no
446          // special treatment of this case is required.
447          watch_entry->watch_ =
448              g_inotify_reader.Get().AddWatch(link.DirName(), this);
449          if (watch_entry->watch_ != InotifyReader::kInvalidWatch) {
450            watch_entry->linkname_ = link.BaseName().value();
451          } else {
452            DPLOG(WARNING) << "Watch failed for "  << link.DirName().value();
453            // TODO(craig) Symlinks only work if the parent directory
454            // for the target exist. Ideally we should make sure we've
455            // watched all the components of the symlink path for
456            // changes. See crbug.com/91561 for details.
457          }
458        }
459      }
460      if (watch_entry->watch_ == InotifyReader::kInvalidWatch) {
461        path_valid = false;
462      }
463    } else {
464      watch_entry->watch_ = InotifyReader::kInvalidWatch;
465    }
466    if (old_watch != InotifyReader::kInvalidWatch &&
467        old_watch != watch_entry->watch_) {
468      g_inotify_reader.Get().RemoveWatch(old_watch, this);
469    }
470    path = path.Append(watch_entry->subdir_);
471  }
472
473  return true;
474}
475
476}  // namespace
477
478FilePathWatcher::FilePathWatcher() {
479  impl_ = new FilePathWatcherImpl();
480}
481
482}  // namespace files
483}  // namespace base
484