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      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
    494