base/files/file_path_watcher_linux.cc

   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
  34 namespace base {
  35
  36 namespace {
  37
  38 class 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
  43 class 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 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
  87 class 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                      bool recursive,
 104                      const FilePathWatcher::Callback& callback) 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  protected:
 115   virtual ~FilePathWatcherImpl() {}
 116
 117  private:
 118   // Cleans up and stops observing the |message_loop_| thread.
 119   virtual void CancelOnMessageLoopThread() 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     WatchEntry(InotifyReader::Watch watch, const FilePath::StringType& subdir)
 127         : watch_(watch),
 128           subdir_(subdir) {}
 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   // Callback to notify upon changes.
 141   FilePathWatcher::Callback callback_;
 142
 143   // The file or directory we're supposed to watch.
 144   FilePath target_;
 145
 146   // The vector of watches and next component names for all path components,
 147   // starting at the root directory. The last entry corresponds to the watch for
 148   // |target_| and always stores an empty next component name in |subdir_|.
 149   WatchVector watches_;
 150
 151   DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
 152 };
 153
 154 void InotifyReaderCallback(InotifyReader* reader, int inotify_fd,
 155                            int shutdown_fd) {
 156   // Make sure the file descriptors are good for use with select().
 157   CHECK_LE(0, inotify_fd);
 158   CHECK_GT(FD_SETSIZE, inotify_fd);
 159   CHECK_LE(0, shutdown_fd);
 160   CHECK_GT(FD_SETSIZE, shutdown_fd);
 161
 162   debug::TraceLog::GetInstance()->SetCurrentThreadBlocksMessageLoop();
 163
 164   while (true) {
 165     fd_set rfds;
 166     FD_ZERO(&rfds);
 167     FD_SET(inotify_fd, &rfds);
 168     FD_SET(shutdown_fd, &rfds);
 169
 170     // Wait until some inotify events are available.
 171     int select_result =
 172       HANDLE_EINTR(select(std::max(inotify_fd, shutdown_fd) + 1,
 173                           &rfds, NULL, NULL, NULL));
 174     if (select_result < 0) {
 175       DPLOG(WARNING) << "select failed";
 176       return;
 177     }
 178
 179     if (FD_ISSET(shutdown_fd, &rfds))
 180       return;
 181
 182     // Adjust buffer size to current event queue size.
 183     int buffer_size;
 184     int ioctl_result = HANDLE_EINTR(ioctl(inotify_fd, FIONREAD,
 185                                           &buffer_size));
 186
 187     if (ioctl_result != 0) {
 188       DPLOG(WARNING) << "ioctl failed";
 189       return;
 190     }
 191
 192     std::vector<char> buffer(buffer_size);
 193
 194     ssize_t bytes_read = HANDLE_EINTR(read(inotify_fd, &buffer[0],
 195                                            buffer_size));
 196
 197     if (bytes_read < 0) {
 198       DPLOG(WARNING) << "read from inotify fd failed";
 199       return;
 200     }
 201
 202     ssize_t i = 0;
 203     while (i < bytes_read) {
 204       inotify_event* event = reinterpret_cast<inotify_event*>(&buffer[i]);
 205       size_t event_size = sizeof(inotify_event) + event->len;
 206       DCHECK(i + event_size <= static_cast<size_t>(bytes_read));
 207       reader->OnInotifyEvent(event);
 208       i += event_size;
 209     }
 210   }
 211 }
 212
 213 static LazyInstance<InotifyReader>::Leaky g_inotify_reader =
 214     LAZY_INSTANCE_INITIALIZER;
 215
 216 InotifyReader::InotifyReader()
 217     : thread_("inotify_reader"),
 218       inotify_fd_(inotify_init()),
 219       valid_(false) {
 220   if (inotify_fd_ < 0)
 221     PLOG(ERROR) << "inotify_init() failed";
 222
 223   shutdown_pipe_[0] = -1;
 224   shutdown_pipe_[1] = -1;
 225   if (inotify_fd_ >= 0 && pipe(shutdown_pipe_) == 0 && thread_.Start()) {
 226     thread_.message_loop()->PostTask(
 227         FROM_HERE, Bind(&InotifyReaderCallback, this, inotify_fd_,
 228                               shutdown_pipe_[0]));
 229     valid_ = true;
 230   }
 231 }
 232
 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
 250 InotifyReader::Watch InotifyReader::AddWatch(
 251     const FilePath& path, FilePathWatcherImpl* watcher) {
 252   if (!valid_)
 253     return kInvalidWatch;
 254
 255   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
 270 bool InotifyReader::RemoveWatch(Watch watch,
 271                                 FilePathWatcherImpl* watcher) {
 272   if (!valid_)
 273     return false;
 274
 275   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
 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   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   }
 301 }
 302
 303 FilePathWatcherImpl::FilePathWatcherImpl() {
 304 }
 305
 306 void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
 307                                             const FilePath::StringType& child,
 308                                             bool created) {
 309   if (!message_loop()->BelongsToCurrentThread()) {
 310     // Switch to message_loop_ to access watches_ safely.
 311     message_loop()->PostTask(FROM_HERE,
 312         Bind(&FilePathWatcherImpl::OnFilePathChanged,
 313                    this,
 314                    fired_watch,
 315                    child,
 316                    created));
 317     return;
 318   }
 319
 320   DCHECK(MessageLoopForIO::current());
 321
 322   // Find the entry in |watches_| that corresponds to |fired_watch|.
 323   WatchVector::const_iterator watch_entry(watches_.begin());
 324   for ( ; watch_entry != watches_.end(); ++watch_entry) {
 325     if (fired_watch == watch_entry->watch_) {
 326       // Check whether a path component of |target_| changed.
 327       bool change_on_target_path = child.empty() ||
 328           ((child == watch_entry->subdir_) && watch_entry->linkname_.empty()) ||
 329           (child == watch_entry->linkname_);
 330
 331       // Check whether the change references |target_| or a direct child.
 332       DCHECK(watch_entry->subdir_.empty() ||
 333           (watch_entry + 1) != watches_.end());
 334       bool target_changed =
 335           (watch_entry->subdir_.empty() && (child == watch_entry->linkname_)) ||
 336           (watch_entry->subdir_.empty() && watch_entry->linkname_.empty()) ||
 337           (watch_entry->subdir_ == child && (watch_entry + 1)->subdir_.empty());
 338
 339       // Update watches if a directory component of the |target_| path
 340       // (dis)appears. Note that we don't add the additional restriction
 341       // of checking the event mask to see if it is for a directory here
 342       // as changes to symlinks on the target path will not have
 343       // IN_ISDIR set in the event masks. As a result we may sometimes
 344       // call UpdateWatches() unnecessarily.
 345       if (change_on_target_path && !UpdateWatches()) {
 346         callback_.Run(target_, true /* error */);
 347         return;
 348       }
 349
 350       // Report the following events:
 351       //  - The target or a direct child of the target got changed (in case the
 352       //    watched path refers to a directory).
 353       //  - One of the parent directories got moved or deleted, since the target
 354       //    disappears in this case.
 355       //  - One of the parent directories appears. The event corresponding to
 356       //    the target appearing might have been missed in this case, so
 357       //    recheck.
 358       if (target_changed ||
 359           (change_on_target_path && !created) ||
 360           (change_on_target_path && PathExists(target_))) {
 361         callback_.Run(target_, false);
 362         return;
 363       }
 364     }
 365   }
 366 }
 367
 368 bool FilePathWatcherImpl::Watch(const FilePath& path,
 369                                 bool recursive,
 370                                 const FilePathWatcher::Callback& callback) {
 371   DCHECK(target_.empty());
 372   DCHECK(MessageLoopForIO::current());
 373   if (recursive) {
 374     // Recursive watch is not supported on this platform.
 375     NOTIMPLEMENTED();
 376     return false;
 377   }
 378
 379   set_message_loop(MessageLoopProxy::current().get());
 380   callback_ = callback;
 381   target_ = path;
 382   MessageLoop::current()->AddDestructionObserver(this);
 383
 384   std::vector<FilePath::StringType> comps;
 385   target_.GetComponents(&comps);
 386   DCHECK(!comps.empty());
 387   std::vector<FilePath::StringType>::const_iterator comp = comps.begin();
 388   for (++comp; comp != comps.end(); ++comp)
 389     watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch, *comp));
 390
 391   watches_.push_back(WatchEntry(InotifyReader::kInvalidWatch,
 392                                 FilePath::StringType()));
 393   return UpdateWatches();
 394 }
 395
 396 void FilePathWatcherImpl::Cancel() {
 397   if (callback_.is_null()) {
 398     // Watch was never called, or the |message_loop_| thread is already gone.
 399     set_cancelled();
 400     return;
 401   }
 402
 403   // Switch to the message_loop_ if necessary so we can access |watches_|.
 404   if (!message_loop()->BelongsToCurrentThread()) {
 405     message_loop()->PostTask(FROM_HERE,
 406                              Bind(&FilePathWatcher::CancelWatch,
 407                                         make_scoped_refptr(this)));
 408   } else {
 409     CancelOnMessageLoopThread();
 410   }
 411 }
 412
 413 void FilePathWatcherImpl::CancelOnMessageLoopThread() {
 414   if (!is_cancelled())
 415     set_cancelled();
 416
 417   if (!callback_.is_null()) {
 418     MessageLoop::current()->RemoveDestructionObserver(this);
 419     callback_.Reset();
 420   }
 421
 422   for (WatchVector::iterator watch_entry(watches_.begin());
 423        watch_entry != watches_.end(); ++watch_entry) {
 424     if (watch_entry->watch_ != InotifyReader::kInvalidWatch)
 425       g_inotify_reader.Get().RemoveWatch(watch_entry->watch_, this);
 426   }
 427   watches_.clear();
 428   target_.clear();
 429 }
 430
 431 void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
 432   CancelOnMessageLoopThread();
 433 }
 434
 435 bool FilePathWatcherImpl::UpdateWatches() {
 436   // Ensure this runs on the |message_loop_| exclusively in order to avoid
 437   // concurrency issues.
 438   DCHECK(message_loop()->BelongsToCurrentThread());
 439
 440   // Walk the list of watches and update them as we go.
 441   FilePath path(FILE_PATH_LITERAL("/"));
 442   bool path_valid = true;
 443   for (WatchVector::iterator watch_entry(watches_.begin());
 444        watch_entry != watches_.end(); ++watch_entry) {
 445     InotifyReader::Watch old_watch = watch_entry->watch_;
 446     if (path_valid) {
 447       watch_entry->watch_ = g_inotify_reader.Get().AddWatch(path, this);
 448       if ((watch_entry->watch_ == InotifyReader::kInvalidWatch) &&
 449           base::IsLink(path)) {
 450         FilePath link;
 451         if (ReadSymbolicLink(path, &link)) {
 452           if (!link.IsAbsolute())
 453             link = path.DirName().Append(link);
 454           // Try watching symlink target directory. If the link target is "/",
 455           // then we shouldn't get here in normal situations and if we do, we'd
 456           // watch "/" for changes to a component "/" which is harmless so no
 457           // special treatment of this case is required.
 458           watch_entry->watch_ =
 459               g_inotify_reader.Get().AddWatch(link.DirName(), this);
 460           if (watch_entry->watch_ != InotifyReader::kInvalidWatch) {
 461             watch_entry->linkname_ = link.BaseName().value();
 462           } else {
 463             DPLOG(WARNING) << "Watch failed for "  << link.DirName().value();
 464             // TODO(craig) Symlinks only work if the parent directory
 465             // for the target exist. Ideally we should make sure we've
 466             // watched all the components of the symlink path for
 467             // changes. See crbug.com/91561 for details.
 468           }
 469         }
 470       }
 471       if (watch_entry->watch_ == InotifyReader::kInvalidWatch) {
 472         path_valid = false;
 473       }
 474     } else {
 475       watch_entry->watch_ = InotifyReader::kInvalidWatch;
 476     }
 477     if (old_watch != InotifyReader::kInvalidWatch &&
 478         old_watch != watch_entry->watch_) {
 479       g_inotify_reader.Get().RemoveWatch(old_watch, this);
 480     }
 481     path = path.Append(watch_entry->subdir_);
 482   }
 483
 484   return true;
 485 }
 486
 487 }  // namespace
 488
 489 FilePathWatcher::FilePathWatcher() {
 490   impl_ = new FilePathWatcherImpl();
 491 }
 492
 493 }  // namespace base