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