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/file_util.h"
  21 #include "base/files/file_path.h"
  22 #include "base/hash_tables.h"
  23 #include "base/lazy_instance.h"
  24 #include "base/location.h"
  25 #include "base/logging.h"
  26 #include "base/memory/scoped_ptr.h"
  27 #include "base/message_loop.h"
  28 #include "base/message_loop_proxy.h"
  29 #include "base/posix/eintr_wrapper.h"
  30 #include "base/synchronization/lock.h"
  31 #include "base/threading/thread.h"
  32
  33 namespace base {
  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.
  95   void OnFilePathChanged(InotifyReader::Watch fired_watch,
  96                          const FilePath::StringType& child,
  97                          bool created);
  98
  99   // Start watching |path| for changes and notify |delegate| on each change.
 100   // Returns true if watch for |path| has been added successfully.
 101   virtual bool Watch(const FilePath& path,
 102                      bool recursive,
 103                      const FilePathWatcher::Callback& callback) 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   // Callback to notify upon changes.
 140   FilePathWatcher::Callback callback_;
 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
 153 void 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
 210 static base::LazyInstance<InotifyReader>::Leaky g_inotify_reader =
 211     LAZY_INSTANCE_INITIALIZER;
 212
 213 InotifyReader::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
 227 InotifyReader::~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
 244 InotifyReader::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
 264 bool 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
 281 void 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
 297 FilePathWatcherImpl::FilePathWatcherImpl() {
 298 }
 299
 300 void FilePathWatcherImpl::OnFilePathChanged(InotifyReader::Watch fired_watch,
 301                                             const FilePath::StringType& child,
 302                                             bool created) {
 303   if (!message_loop()->BelongsToCurrentThread()) {
 304     // Switch to message_loop_ to access watches_ safely.
 305     message_loop()->PostTask(FROM_HERE,
 306         base::Bind(&FilePathWatcherImpl::OnFilePathChanged,
 307                    this,
 308                    fired_watch,
 309                    child,
 310                    created));
 311     return;
 312   }
 313
 314   DCHECK(MessageLoopForIO::current());
 315
 316   // Find the entry in |watches_| that corresponds to |fired_watch|.
 317   WatchVector::const_iterator watch_entry(watches_.begin());
 318   for ( ; watch_entry != watches_.end(); ++watch_entry) {
 319     if (fired_watch == watch_entry->watch_) {
 320       // Check whether a path component of |target_| changed.
 321       bool change_on_target_path = child.empty() ||
 322           ((child == watch_entry->subdir_) && watch_entry->linkname_.empty()) ||
 323           (child == watch_entry->linkname_);
 324
 325       // Check whether the change references |target_| or a direct child.
 326       DCHECK(watch_entry->subdir_.empty() ||
 327           (watch_entry + 1) != watches_.end());
 328       bool target_changed =
 329           (watch_entry->subdir_.empty() && (child == watch_entry->linkname_)) ||
 330           (watch_entry->subdir_.empty() && watch_entry->linkname_.empty()) ||
 331           (watch_entry->subdir_ == child && (watch_entry + 1)->subdir_.empty());
 332
 333       // Update watches if a directory component of the |target_| path
 334       // (dis)appears. Note that we don't add the additional restriction
 335       // of checking the event mask to see if it is for a directory here
 336       // as changes to symlinks on the target path will not have
 337       // IN_ISDIR set in the event masks. As a result we may sometimes
 338       // call UpdateWatches() unnecessarily.
 339       if (change_on_target_path && !UpdateWatches()) {
 340         callback_.Run(target_, true /* error */);
 341         return;
 342       }
 343
 344       // Report the following events:
 345       //  - The target or a direct child of the target got changed (in case the
 346       //    watched path refers to a directory).
 347       //  - One of the parent directories got moved or deleted, since the target
 348       //    disappears in this case.
 349       //  - One of the parent directories appears. The event corresponding to
 350       //    the target appearing might have been missed in this case, so
 351       //    recheck.
 352       if (target_changed ||
 353           (change_on_target_path && !created) ||
 354           (change_on_target_path && file_util::PathExists(target_))) {
 355         callback_.Run(target_, false);
 356         return;
 357       }
 358     }
 359   }
 360 }
 361
 362 bool FilePathWatcherImpl::Watch(const FilePath& path,
 363                                 bool recursive,
 364                                 const FilePathWatcher::Callback& callback) {
 365   DCHECK(target_.empty());
 366   DCHECK(MessageLoopForIO::current());
 367   if (recursive) {
 368     // Recursive watch is not supported on this platform.
 369     NOTIMPLEMENTED();
 370     return false;
 371   }
 372
 373   set_message_loop(base::MessageLoopProxy::current());
 374   callback_ = callback;
 375   target_ = path;
 376   MessageLoop::current()->AddDestructionObserver(this);
 377
 378   std::vector<FilePath::StringType> comps;
 379   target_.GetComponents(&comps);
 380   DCHECK(!comps.empty());
 381   std::vector<FilePath::StringType>::const_iterator comp = comps.begin();
 382   for (++comp; 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
 390 void FilePathWatcherImpl::Cancel() {
 391   if (callback_.is_null()) {
 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                              base::Bind(&FilePathWatcher::CancelWatch,
 401                                         make_scoped_refptr(this)));
 402   } else {
 403     CancelOnMessageLoopThread();
 404   }
 405 }
 406
 407 void FilePathWatcherImpl::CancelOnMessageLoopThread() {
 408   if (!is_cancelled())
 409     set_cancelled();
 410
 411   if (!callback_.is_null()) {
 412     MessageLoop::current()->RemoveDestructionObserver(this);
 413     callback_.Reset();
 414   }
 415
 416   for (WatchVector::iterator watch_entry(watches_.begin());
 417        watch_entry != watches_.end(); ++watch_entry) {
 418     if (watch_entry->watch_ != InotifyReader::kInvalidWatch)
 419       g_inotify_reader.Get().RemoveWatch(watch_entry->watch_, this);
 420   }
 421   watches_.clear();
 422   target_.clear();
 423 }
 424
 425 void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
 426   CancelOnMessageLoopThread();
 427 }
 428
 429 bool FilePathWatcherImpl::UpdateWatches() {
 430   // Ensure this runs on the |message_loop_| exclusively in order to avoid
 431   // concurrency issues.
 432   DCHECK(message_loop()->BelongsToCurrentThread());
 433
 434   // Walk the list of watches and update them as we go.
 435   FilePath path(FILE_PATH_LITERAL("/"));
 436   bool path_valid = true;
 437   for (WatchVector::iterator watch_entry(watches_.begin());
 438        watch_entry != watches_.end(); ++watch_entry) {
 439     InotifyReader::Watch old_watch = watch_entry->watch_;
 440     if (path_valid) {
 441       watch_entry->watch_ = g_inotify_reader.Get().AddWatch(path, this);
 442       if ((watch_entry->watch_ == InotifyReader::kInvalidWatch) &&
 443           file_util::IsLink(path)) {
 444         FilePath link;
 445         if (file_util::ReadSymbolicLink(path, &link)) {
 446           if (!link.IsAbsolute())
 447             link = path.DirName().Append(link);
 448           // Try watching symlink target directory. If the link target is "/",
 449           // then we shouldn't get here in normal situations and if we do, we'd
 450           // watch "/" for changes to a component "/" which is harmless so no
 451           // special treatment of this case is required.
 452           watch_entry->watch_ =
 453               g_inotify_reader.Get().AddWatch(link.DirName(), this);
 454           if (watch_entry->watch_ != InotifyReader::kInvalidWatch) {
 455             watch_entry->linkname_ = link.BaseName().value();
 456           } else {
 457             DPLOG(WARNING) << "Watch failed for "  << link.DirName().value();
 458             // TODO(craig) Symlinks only work if the parent directory
 459             // for the target exist. Ideally we should make sure we've
 460             // watched all the components of the symlink path for
 461             // changes. See crbug.com/91561 for details.
 462           }
 463         }
 464       }
 465       if (watch_entry->watch_ == InotifyReader::kInvalidWatch) {
 466         path_valid = false;
 467       }
 468     } else {
 469       watch_entry->watch_ = InotifyReader::kInvalidWatch;
 470     }
 471     if (old_watch != InotifyReader::kInvalidWatch &&
 472         old_watch != watch_entry->watch_) {
 473       g_inotify_reader.Get().RemoveWatch(old_watch, this);
 474     }
 475     path = path.Append(watch_entry->subdir_);
 476   }
 477
 478   return true;
 479 }
 480
 481 }  // namespace
 482
 483 FilePathWatcher::FilePathWatcher() {
 484   impl_ = new FilePathWatcherImpl();
 485 }
 486
 487 }  // namespace base