file_path_watcher_linux.cc revision 5c02ac1a9c1b504631c0a3d2b6e737b5d738bae1 
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/containers/hash_tables.h"
21#include "base/debug/trace_event.h"
22#include "base/file_util.h"
23#include "base/files/file_path.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/message_loop.h"
29#include "base/message_loop/message_loop_proxy.h"
30#include "base/posix/eintr_wrapper.h"
31#include "base/synchronization/lock.h"
32#include "base/threading/thread.h"
33
34namespace base {
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| if it's valid.
53  void RemoveWatch(Watch watch, FilePathWatcherImpl* watcher);
54
55  // Callback for InotifyReaderTask.
56  void OnInotifyEvent(const inotify_event* event);
57
58 private:
59  friend struct 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  hash_map<Watch, WatcherSet> watchers_;
68
69  // Lock to protect watchers_.
70  Lock lock_;
71
72  // Separate thread on which we run blocking read for inotify events.
73  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 protected:
101  virtual ~FilePathWatcherImpl() {}
102
103 private:
104  // Start watching |path| for changes and notify |delegate| on each change.
105  // Returns true if watch for |path| has been added successfully.
106  virtual bool Watch(const FilePath& path,
107                     bool recursive,
108                     const FilePathWatcher::Callback& callback) OVERRIDE;
109
110  // Cancel the watch. This unregisters the instance with InotifyReader.
111  virtual void Cancel() OVERRIDE;
112
113  // Cleans up and stops observing the message_loop() thread.
114  virtual void CancelOnMessageLoopThread() OVERRIDE;
115
116  // Deletion of the FilePathWatcher will call Cancel() to dispose of this
117  // object in the right thread. This also observes destruction of the required
118  // cleanup thread, in case it quits before Cancel() is called.
119  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
120
121  // Inotify watches are installed for all directory components of |target_|. A
122  // WatchEntry instance holds the watch descriptor for a component and the
123  // subdirectory for that identifies the next component. If a symbolic link
124  // is being watched, the target of the link is also kept.
125  struct WatchEntry {
126    explicit WatchEntry(const FilePath::StringType& dirname)
127        : watch(InotifyReader::kInvalidWatch),
128          subdir(dirname) {}
129
130    InotifyReader::Watch watch;
131    FilePath::StringType subdir;
132    FilePath::StringType linkname;
133  };
134  typedef std::vector<WatchEntry> WatchVector;
135
136  // Reconfigure to watch for the most specific parent directory of |target_|
137  // that exists. Updates |watched_path_|. Returns true on success.
138  bool UpdateWatches() WARN_UNUSED_RESULT;
139
140  // |path| is a symlink to a non-existent target. Attempt to add a watch to
141  // the link target's parent directory. Returns true and update |watch_entry|
142  // on success.
143  bool AddWatchForBrokenSymlink(const FilePath& path, WatchEntry* watch_entry);
144
145  bool HasValidWatchVector() const;
146
147  // Callback to notify upon changes.
148  FilePathWatcher::Callback callback_;
149
150  // The file or directory we're supposed to watch.
151  FilePath target_;
152
153  // The vector of watches and next component names for all path components,
154  // starting at the root directory. The last entry corresponds to the watch for
155  // |target_| and always stores an empty next component name in |subdir|.
156  WatchVector watches_;
157
158  DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
159};
160
161void InotifyReaderCallback(InotifyReader* reader, int inotify_fd,
162                           int shutdown_fd) {
163  // Make sure the file descriptors are good for use with select().
164  CHECK_LE(0, inotify_fd);
165  CHECK_GT(FD_SETSIZE, inotify_fd);
166  CHECK_LE(0, shutdown_fd);
167  CHECK_GT(FD_SETSIZE, shutdown_fd);
168
169  debug::TraceLog::GetInstance()->SetCurrentThreadBlocksMessageLoop();
170
171  while (true) {
172    fd_set rfds;
173    FD_ZERO(&rfds);
174    FD_SET(inotify_fd, &rfds);
175    FD_SET(shutdown_fd, &rfds);
176
177    // Wait until some inotify events are available.
178    int select_result =
179      HANDLE_EINTR(select(std::max(inotify_fd, shutdown_fd) + 1,
180                          &rfds, NULL, NULL, NULL));
181    if (select_result < 0) {
182      DPLOG(WARNING) << "select failed";
183      return;
184    }
185
186    if (FD_ISSET(shutdown_fd, &rfds))
187      return;
188
189    // Adjust buffer size to current event queue size.
190    int buffer_size;
191    int ioctl_result = HANDLE_EINTR(ioctl(inotify_fd, FIONREAD,
192                                          &buffer_size));
193
194    if (ioctl_result != 0) {
195      DPLOG(WARNING) << "ioctl failed";
196      return;
197    }
198
199    std::vector<char> buffer(buffer_size);
200
201    ssize_t bytes_read = HANDLE_EINTR(read(inotify_fd, &buffer[0],
202                                           buffer_size));
203
204    if (bytes_read < 0) {
205      DPLOG(WARNING) << "read from inotify fd failed";
206      return;
207    }
208
209    ssize_t i = 0;
210    while (i < bytes_read) {
211      inotify_event* event = reinterpret_cast<inotify_event*>(&buffer[i]);
212      size_t event_size = sizeof(inotify_event) + event->len;
213      DCHECK(i + event_size <= static_cast<size_t>(bytes_read));
214      reader->OnInotifyEvent(event);
215      i += event_size;
216    }
217  }
218}
219
220static LazyInstance<InotifyReader>::Leaky g_inotify_reader =
221    LAZY_INSTANCE_INITIALIZER;
222
223InotifyReader::InotifyReader()
224    : thread_("inotify_reader"),
225      inotify_fd_(inotify_init()),
226      valid_(false) {
227  if (inotify_fd_ < 0)
228    PLOG(ERROR) << "inotify_init() failed";
229
230  shutdown_pipe_[0] = -1;
231  shutdown_pipe_[1] = -1;
232  if (inotify_fd_ >= 0 && pipe(shutdown_pipe_) == 0 && thread_.Start()) {
233    thread_.message_loop()->PostTask(
234        FROM_HERE,
235        Bind(&InotifyReaderCallback, this, inotify_fd_, shutdown_pipe_[0]));
236    valid_ = true;
237  }
238}
239
240InotifyReader::~InotifyReader() {
241  if (valid_) {
242    // Write to the self-pipe so that the select call in InotifyReaderTask
243    // returns.
244    ssize_t ret = HANDLE_EINTR(write(shutdown_pipe_[1], "", 1));
245    DPCHECK(ret > 0);
246    DCHECK_EQ(ret, 1);
247    thread_.Stop();
248  }
249  if (inotify_fd_ >= 0)
250    close(inotify_fd_);
251  if (shutdown_pipe_[0] >= 0)
252    close(shutdown_pipe_[0]);
253  if (shutdown_pipe_[1] >= 0)
254    close(shutdown_pipe_[1]);
255}
256
257InotifyReader::Watch InotifyReader::AddWatch(
258    const FilePath& path, FilePathWatcherImpl* watcher) {
259  if (!valid_)
260    return kInvalidWatch;
261
262  AutoLock auto_lock(lock_);
263
264  Watch watch = inotify_add_watch(inotify_fd_, path.value().c_str(),
265                                  IN_CREATE | IN_DELETE |
266                                  IN_CLOSE_WRITE | IN_MOVE |
267                                  IN_ONLYDIR);
268
269  if (watch == kInvalidWatch)
270    return kInvalidWatch;
271
272  watchers_[watch].insert(watcher);
273
274  return watch;
275}
276
277void InotifyReader::RemoveWatch(Watch watch, FilePathWatcherImpl* watcher) {
278  if (!valid_ || (watch == kInvalidWatch))
279    return;
280
281  AutoLock auto_lock(lock_);
282
283  watchers_[watch].erase(watcher);
284
285  if (watchers_[watch].empty()) {
286    watchers_.erase(watch);
287    inotify_rm_watch(inotify_fd_, watch);
288  }
289}
290
291void InotifyReader::OnInotifyEvent(const inotify_event* event) {
292  if (event->mask & IN_IGNORED)
293    return;
294
295  FilePath::StringType child(event->len ? event->name : FILE_PATH_LITERAL(""));
296  AutoLock auto_lock(lock_);
297
298  for (WatcherSet::iterator watcher = watchers_[event->wd].begin();
299       watcher != watchers_[event->wd].end();
300       ++watcher) {
301    (*watcher)->OnFilePathChanged(event->wd,
302                                  child,
303                                  event->mask & (IN_CREATE | IN_MOVED_TO));
304  }
305}
306
307FilePathWatcherImpl::FilePathWatcherImpl() {
308}
309
310void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
311                                            const FilePath::StringType& child,
312                                            bool created) {
313  if (!message_loop()->BelongsToCurrentThread()) {
314    // Switch to message_loop() to access |watches_| safely.
315    message_loop()->PostTask(
316        FROM_HERE,
317        Bind(&FilePathWatcherImpl::OnFilePathChanged, this,
318             fired_watch, child, created));
319    return;
320  }
321
322  // Check to see if CancelOnMessageLoopThread() has already been called.
323  // May happen when code flow reaches here from the PostTask() above.
324  if (watches_.empty()) {
325    DCHECK(target_.empty());
326    return;
327  }
328
329  DCHECK(MessageLoopForIO::current());
330  DCHECK(HasValidWatchVector());
331
332  // Find the entry in |watches_| that corresponds to |fired_watch|.
333  for (size_t i = 0; i < watches_.size(); ++i) {
334    const WatchEntry& watch_entry = watches_[i];
335    if (fired_watch != watch_entry.watch)
336      continue;
337
338    // Check whether a path component of |target_| changed.
339    bool change_on_target_path =
340        child.empty() ||
341        (child == watch_entry.linkname) ||
342        (child == watch_entry.subdir);
343
344    // Check if the change references |target_| or a direct child of |target_|.
345    bool is_watch_for_target = watch_entry.subdir.empty();
346    bool target_changed =
347        (is_watch_for_target && (child == watch_entry.linkname)) ||
348        (is_watch_for_target && watch_entry.linkname.empty()) ||
349        (watch_entry.subdir == child && watches_[i + 1].subdir.empty());
350
351    // Update watches if a directory component of the |target_| path
352    // (dis)appears. Note that we don't add the additional restriction of
353    // checking the event mask to see if it is for a directory here as changes
354    // to symlinks on the target path will not have IN_ISDIR set in the event
355    // masks. As a result we may sometimes call UpdateWatches() unnecessarily.
356    if (change_on_target_path && !UpdateWatches()) {
357      callback_.Run(target_, true /* error */);
358      return;
359    }
360
361    // Report the following events:
362    //  - The target or a direct child of the target got changed (in case the
363    //    watched path refers to a directory).
364    //  - One of the parent directories got moved or deleted, since the target
365    //    disappears in this case.
366    //  - One of the parent directories appears. The event corresponding to
367    //    the target appearing might have been missed in this case, so recheck.
368    if (target_changed ||
369        (change_on_target_path && !created) ||
370        (change_on_target_path && PathExists(target_))) {
371      callback_.Run(target_, false /* error */);
372      return;
373    }
374  }
375}
376
377bool FilePathWatcherImpl::Watch(const FilePath& path,
378                                bool recursive,
379                                const FilePathWatcher::Callback& callback) {
380  DCHECK(target_.empty());
381  DCHECK(MessageLoopForIO::current());
382  if (recursive) {
383    // Recursive watch is not supported on this platform.
384    NOTIMPLEMENTED();
385    return false;
386  }
387
388  set_message_loop(MessageLoopProxy::current().get());
389  callback_ = callback;
390  target_ = path;
391  MessageLoop::current()->AddDestructionObserver(this);
392
393  std::vector<FilePath::StringType> comps;
394  target_.GetComponents(&comps);
395  DCHECK(!comps.empty());
396  for (size_t i = 1; i < comps.size(); ++i)
397    watches_.push_back(WatchEntry(comps[i]));
398  watches_.push_back(WatchEntry(FilePath::StringType()));
399  return UpdateWatches();
400}
401
402void FilePathWatcherImpl::Cancel() {
403  if (callback_.is_null()) {
404    // Watch was never called, or the message_loop() thread is already gone.
405    set_cancelled();
406    return;
407  }
408
409  // Switch to the message_loop() if necessary so we can access |watches_|.
410  if (!message_loop()->BelongsToCurrentThread()) {
411    message_loop()->PostTask(FROM_HERE,
412                             Bind(&FilePathWatcher::CancelWatch,
413                                  make_scoped_refptr(this)));
414  } else {
415    CancelOnMessageLoopThread();
416  }
417}
418
419void FilePathWatcherImpl::CancelOnMessageLoopThread() {
420  set_cancelled();
421
422  if (!callback_.is_null()) {
423    MessageLoop::current()->RemoveDestructionObserver(this);
424    callback_.Reset();
425  }
426
427  for (size_t i = 0; i < watches_.size(); ++i)
428    g_inotify_reader.Get().RemoveWatch(watches_[i].watch, this);
429  watches_.clear();
430  target_.clear();
431}
432
433void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
434  CancelOnMessageLoopThread();
435}
436
437bool FilePathWatcherImpl::UpdateWatches() {
438  // Ensure this runs on the message_loop() exclusively in order to avoid
439  // concurrency issues.
440  DCHECK(message_loop()->BelongsToCurrentThread());
441  DCHECK(HasValidWatchVector());
442
443  // Walk the list of watches and update them as we go.
444  FilePath path(FILE_PATH_LITERAL("/"));
445  bool path_valid = true;
446  for (size_t i = 0; i < watches_.size(); ++i) {
447    WatchEntry& watch_entry = watches_[i];
448    InotifyReader::Watch old_watch = watch_entry.watch;
449    watch_entry.watch = InotifyReader::kInvalidWatch;
450    watch_entry.linkname.clear();
451    if (path_valid) {
452      watch_entry.watch = g_inotify_reader.Get().AddWatch(path, this);
453      if (watch_entry.watch == InotifyReader::kInvalidWatch) {
454        if (IsLink(path)) {
455          path_valid = AddWatchForBrokenSymlink(path, &watch_entry);
456        } else {
457          path_valid = false;
458        }
459      }
460    }
461    if (old_watch != watch_entry.watch)
462      g_inotify_reader.Get().RemoveWatch(old_watch, this);
463    path = path.Append(watch_entry.subdir);
464  }
465
466  return true;
467}
468
469bool FilePathWatcherImpl::AddWatchForBrokenSymlink(const FilePath& path,
470                                                   WatchEntry* watch_entry) {
471  DCHECK_EQ(InotifyReader::kInvalidWatch, watch_entry->watch);
472  FilePath link;
473  if (!ReadSymbolicLink(path, &link))
474    return false;
475
476  if (!link.IsAbsolute())
477    link = path.DirName().Append(link);
478
479  // Try watching symlink target directory. If the link target is "/", then we
480  // shouldn't get here in normal situations and if we do, we'd watch "/" for
481  // changes to a component "/" which is harmless so no special treatment of
482  // this case is required.
483  InotifyReader::Watch watch =
484      g_inotify_reader.Get().AddWatch(link.DirName(), this);
485  if (watch == InotifyReader::kInvalidWatch) {
486    // TODO(craig) Symlinks only work if the parent directory for the target
487    // exist. Ideally we should make sure we've watched all the components of
488    // the symlink path for changes. See crbug.com/91561 for details.
489    DPLOG(WARNING) << "Watch failed for "  << link.DirName().value();
490    return false;
491  }
492  watch_entry->watch = watch;
493  watch_entry->linkname = link.BaseName().value();
494  return true;
495}
496
497bool FilePathWatcherImpl::HasValidWatchVector() const {
498  if (watches_.empty())
499    return false;
500  for (size_t i = 0; i < watches_.size() - 1; ++i) {
501    if (watches_[i].subdir.empty())
502      return false;
503  }
504  return watches_[watches_.size() - 1].subdir.empty();
505}
506
507}  // namespace
508
509FilePathWatcher::FilePathWatcher() {
510  impl_ = new FilePathWatcherImpl();
511}
512
513}  // namespace base
514