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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 
32 namespace base {
33 namespace files {
34 
35 namespace {
36 
37 class 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
42 class 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 
86 class 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:
~FilePathWatcherImpl()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 {
WatchEntrybase::files::__anon483d23560111::FilePathWatcherImpl::WatchEntry124     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 
151 class InotifyReaderTask : public Task {
152  public:
InotifyReaderTask(InotifyReader * reader,int inotify_fd,int shutdown_fd)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 
Run()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 
217 static base::LazyInstance<InotifyReader> g_inotify_reader(
218     base::LINKER_INITIALIZED);
219 
InotifyReader()220 InotifyReader::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 
~InotifyReader()233 InotifyReader::~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 
AddWatch(const FilePath & path,FilePathWatcherImpl * watcher)250 InotifyReader::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 
RemoveWatch(Watch watch,FilePathWatcherImpl * watcher)270 bool 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 
OnInotifyEvent(const inotify_event * event)287 void 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 
FilePathWatcherImpl()304 FilePathWatcherImpl::FilePathWatcherImpl()
305     : delegate_(NULL) {
306 }
307 
OnFilePathChanged(InotifyReader::Watch fired_watch,const FilePath::StringType & child,bool created,bool is_directory)308 void 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 
Watch(const FilePath & path,FilePathWatcher::Delegate * delegate)368 bool 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 
Cancel()390 void 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 
CancelOnMessageLoopThread()406 void 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 
WillDestroyCurrentMessageLoop()422 void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
423   CancelOnMessageLoopThread();
424 }
425 
UpdateWatches()426 bool 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 
FilePathWatcher()457 FilePathWatcher::FilePathWatcher() {
458   impl_ = new FilePathWatcherImpl();
459 }
460 
461 }  // namespace files
462 }  // namespace base
463