// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/files/file_path_watcher.h"
#include <fcntl.h>
#include <sys/event.h>
#include <sys/param.h>
#include <vector>
#include "base/file_util.h"
#include "base/message_loop.h"
#include "base/message_loop_proxy.h"
#include "base/stringprintf.h"
namespace base {
namespace files {
namespace {
// Mac-specific file watcher implementation based on kqueue.
// Originally it was based on FSEvents so that the semantics were equivalent
// on Linux, OSX and Windows where it was able to detect:
// - file creation/deletion/modification in a watched directory
// - file creation/deletion/modification for a watched file
// - modifications to the paths to a watched object that would affect the
// object such as renaming/attibute changes etc.
// The FSEvents version did all of the above except handling attribute changes
// to path components. Unfortunately FSEvents appears to have an issue where the
// current implementation (Mac OS X 10.6.7) sometimes drops events and doesn't
// send notifications. See
// http://code.google.com/p/chromium/issues/detail?id=54822#c31 for source that
// will reproduce the problem. FSEvents also required having a CFRunLoop
// backing the thread that it was running on, that caused added complexity
// in the interfaces.
// The kqueue implementation will handle all of the items in the list above
// except for detecting modifications to files in a watched directory. It will
// detect the creation and deletion of files, just not the modification of
// files. It does however detect the attribute changes that the FSEvents impl
// would miss.
class FilePathWatcherImpl : public FilePathWatcher::PlatformDelegate,
public MessageLoopForIO::Watcher,
public MessageLoop::DestructionObserver {
public:
FilePathWatcherImpl() : kqueue_(-1) {}
virtual ~FilePathWatcherImpl() {}
// MessageLoopForIO::Watcher overrides.
virtual void OnFileCanReadWithoutBlocking(int fd) OVERRIDE;
virtual void OnFileCanWriteWithoutBlocking(int fd) OVERRIDE;
// MessageLoop::DestructionObserver overrides.
virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
// FilePathWatcher::PlatformDelegate overrides.
virtual bool Watch(const FilePath& path,
FilePathWatcher::Delegate* delegate) OVERRIDE;
virtual void Cancel() OVERRIDE;
private:
class EventData {
public:
EventData(const FilePath& path, const FilePath::StringType& subdir)
: path_(path), subdir_(subdir) { }
FilePath path_; // Full path to this item.
FilePath::StringType subdir_; // Path to any sub item.
};
typedef std::vector<struct kevent> EventVector;
// Can only be called on |io_message_loop_|'s thread.
virtual void CancelOnMessageLoopThread() OVERRIDE;
// Returns true if the kevent values are error free.
bool AreKeventValuesValid(struct kevent* kevents, int count);
// Respond to a change of attributes of the path component represented by
// |event|. Sets |target_file_affected| to true if |target_| is affected.
// Sets |update_watches| to true if |events_| need to be updated.
void HandleAttributesChange(const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches);
// Respond to a move of deletion of the path component represented by
// |event|. Sets |target_file_affected| to true if |target_| is affected.
// Sets |update_watches| to true if |events_| need to be updated.
void HandleDeleteOrMoveChange(const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches);
// Respond to a creation of an item in the path component represented by
// |event|. Sets |target_file_affected| to true if |target_| is affected.
// Sets |update_watches| to true if |events_| need to be updated.
void HandleCreateItemChange(const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches);
// Update |events_| with the current status of the system.
// Sets |target_file_affected| to true if |target_| is affected.
// Returns false if an error occurs.
bool UpdateWatches(bool* target_file_affected);
// Fills |events| with one kevent per component in |path|.
// Returns the number of valid events created where a valid event is
// defined as one that has a ident (file descriptor) field != -1.
static int EventsForPath(FilePath path, EventVector *events);
// Release a kevent generated by EventsForPath.
static void ReleaseEvent(struct kevent& event);
// Returns a file descriptor that will not block the system from deleting
// the file it references.
static int FileDescriptorForPath(const FilePath& path);
// Closes |*fd| and sets |*fd| to -1.
static void CloseFileDescriptor(int* fd);
// Returns true if kevent has open file descriptor.
static bool IsKeventFileDescriptorOpen(const struct kevent& event) {
return event.ident != static_cast<uintptr_t>(-1);
}
static EventData* EventDataForKevent(const struct kevent& event) {
return reinterpret_cast<EventData*>(event.udata);
}
EventVector events_;
scoped_refptr<base::MessageLoopProxy> io_message_loop_;
MessageLoopForIO::FileDescriptorWatcher kqueue_watcher_;
scoped_refptr<FilePathWatcher::Delegate> delegate_;
FilePath target_;
int kqueue_;
DISALLOW_COPY_AND_ASSIGN(FilePathWatcherImpl);
};
void FilePathWatcherImpl::ReleaseEvent(struct kevent& event) {
CloseFileDescriptor(reinterpret_cast<int*>(&event.ident));
EventData* entry = EventDataForKevent(event);
delete entry;
event.udata = NULL;
}
int FilePathWatcherImpl::EventsForPath(FilePath path, EventVector* events) {
DCHECK(MessageLoopForIO::current());
// Make sure that we are working with a clean slate.
DCHECK(events->empty());
std::vector<FilePath::StringType> components;
path.GetComponents(&components);
if (components.size() < 1) {
return -1;
}
int last_existing_entry = 0;
FilePath built_path;
bool path_still_exists = true;
for(std::vector<FilePath::StringType>::iterator i = components.begin();
i != components.end(); ++i) {
if (i == components.begin()) {
built_path = FilePath(*i);
} else {
built_path = built_path.Append(*i);
}
int fd = -1;
if (path_still_exists) {
fd = FileDescriptorForPath(built_path);
if (fd == -1) {
path_still_exists = false;
} else {
++last_existing_entry;
}
}
FilePath::StringType subdir = (i != (components.end() - 1)) ? *(i + 1) : "";
EventData* data = new EventData(built_path, subdir);
struct kevent event;
EV_SET(&event, fd, EVFILT_VNODE, (EV_ADD | EV_CLEAR | EV_RECEIPT),
(NOTE_DELETE | NOTE_WRITE | NOTE_ATTRIB |
NOTE_RENAME | NOTE_REVOKE | NOTE_EXTEND), 0, data);
events->push_back(event);
}
return last_existing_entry;
}
int FilePathWatcherImpl::FileDescriptorForPath(const FilePath& path) {
return HANDLE_EINTR(open(path.value().c_str(), O_EVTONLY));
}
void FilePathWatcherImpl::CloseFileDescriptor(int *fd) {
if (*fd == -1) {
return;
}
if (HANDLE_EINTR(close(*fd)) != 0) {
PLOG(ERROR) << "close";
}
*fd = -1;
}
bool FilePathWatcherImpl::AreKeventValuesValid(struct kevent* kevents,
int count) {
if (count < 0) {
PLOG(ERROR) << "kevent";
return false;
}
bool valid = true;
for (int i = 0; i < count; ++i) {
if (kevents[i].flags & EV_ERROR && kevents[i].data) {
// Find the kevent in |events_| that matches the kevent with the error.
EventVector::iterator event = events_.begin();
for (; event != events_.end(); ++event) {
if (event->ident == kevents[i].ident) {
break;
}
}
std::string path_name;
if (event != events_.end()) {
EventData* event_data = EventDataForKevent(*event);
if (event_data != NULL) {
path_name = event_data->path_.value();
}
}
if (path_name.empty()) {
path_name = base::StringPrintf(
"fd %d", *reinterpret_cast<int*>(&kevents[i].ident));
}
LOG(ERROR) << "Error: " << kevents[i].data << " for " << path_name;
valid = false;
}
}
return valid;
}
void FilePathWatcherImpl::HandleAttributesChange(
const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches) {
EventVector::iterator next_event = event + 1;
EventData* next_event_data = EventDataForKevent(*next_event);
// Check to see if the next item in path is still accessible.
int have_access = FileDescriptorForPath(next_event_data->path_);
if (have_access == -1) {
*target_file_affected = true;
*update_watches = true;
EventVector::iterator local_event(event);
for (; local_event != events_.end(); ++local_event) {
// Close all nodes from the event down. This has the side effect of
// potentially rendering other events in |updates| invalid.
// There is no need to remove the events from |kqueue_| because this
// happens as a side effect of closing the file descriptor.
CloseFileDescriptor(reinterpret_cast<int*>(&local_event->ident));
}
} else {
CloseFileDescriptor(&have_access);
}
}
void FilePathWatcherImpl::HandleDeleteOrMoveChange(
const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches) {
*target_file_affected = true;
*update_watches = true;
EventVector::iterator local_event(event);
for (; local_event != events_.end(); ++local_event) {
// Close all nodes from the event down. This has the side effect of
// potentially rendering other events in |updates| invalid.
// There is no need to remove the events from |kqueue_| because this
// happens as a side effect of closing the file descriptor.
CloseFileDescriptor(reinterpret_cast<int*>(&local_event->ident));
}
}
void FilePathWatcherImpl::HandleCreateItemChange(
const EventVector::iterator& event,
bool* target_file_affected,
bool* update_watches) {
// Get the next item in the path.
EventVector::iterator next_event = event + 1;
EventData* next_event_data = EventDataForKevent(*next_event);
// Check to see if it already has a valid file descriptor.
if (!IsKeventFileDescriptorOpen(*next_event)) {
// If not, attempt to open a file descriptor for it.
next_event->ident = FileDescriptorForPath(next_event_data->path_);
if (IsKeventFileDescriptorOpen(*next_event)) {
*update_watches = true;
if (next_event_data->subdir_.empty()) {
*target_file_affected = true;
}
}
}
}
bool FilePathWatcherImpl::UpdateWatches(bool* target_file_affected) {
// Iterate over events adding kevents for items that exist to the kqueue.
// Then check to see if new components in the path have been created.
// Repeat until no new components in the path are detected.
// This is to get around races in directory creation in a watched path.
bool update_watches = true;
while (update_watches) {
size_t valid;
for (valid = 0; valid < events_.size(); ++valid) {
if (!IsKeventFileDescriptorOpen(events_[valid])) {
break;
}
}
if (valid == 0) {
// The root of the file path is inaccessible?
return false;
}
EventVector updates(valid);
int count = HANDLE_EINTR(kevent(kqueue_, &events_[0], valid, &updates[0],
valid, NULL));
if (!AreKeventValuesValid(&updates[0], count)) {
return false;
}
update_watches = false;
for (; valid < events_.size(); ++valid) {
EventData* event_data = EventDataForKevent(events_[valid]);
events_[valid].ident = FileDescriptorForPath(event_data->path_);
if (IsKeventFileDescriptorOpen(events_[valid])) {
update_watches = true;
if (event_data->subdir_.empty()) {
*target_file_affected = true;
}
} else {
break;
}
}
}
return true;
}
void FilePathWatcherImpl::OnFileCanReadWithoutBlocking(int fd) {
DCHECK(MessageLoopForIO::current());
CHECK_EQ(fd, kqueue_);
CHECK(events_.size());
// Request the file system update notifications that have occurred and return
// them in |updates|. |count| will contain the number of updates that have
// occurred.
EventVector updates(events_.size());
struct timespec timeout = {0, 0};
int count = HANDLE_EINTR(kevent(kqueue_, NULL, 0, &updates[0], updates.size(),
&timeout));
// Error values are stored within updates, so check to make sure that no
// errors occurred.
if (!AreKeventValuesValid(&updates[0], count)) {
delegate_->OnFilePathError(target_);
Cancel();
return;
}
bool update_watches = false;
bool send_notification = false;
// Iterate through each of the updates and react to them.
for (int i = 0; i < count; ++i) {
// Find our kevent record that matches the update notification.
EventVector::iterator event = events_.begin();
for (; event != events_.end(); ++event) {
if (!IsKeventFileDescriptorOpen(*event) ||
event->ident == updates[i].ident) {
break;
}
}
if (!IsKeventFileDescriptorOpen(*event) || event == events_.end()) {
// The event may no longer exist in |events_| because another event
// modified |events_| in such a way to make it invalid. For example if
// the path is /foo/bar/bam and foo is deleted, NOTE_DELETE events for
// foo, bar and bam will be sent. If foo is processed first, then
// the file descriptors for bar and bam will already be closed and set
// to -1 before they get a chance to be processed.
continue;
}
EventData* event_data = EventDataForKevent(*event);
// If the subdir is empty, this is the last item on the path and is the
// target file.
bool target_file_affected = event_data->subdir_.empty();
if ((updates[i].fflags & NOTE_ATTRIB) && !target_file_affected) {
HandleAttributesChange(event, &target_file_affected, &update_watches);
}
if (updates[i].fflags & (NOTE_DELETE | NOTE_REVOKE | NOTE_RENAME)) {
HandleDeleteOrMoveChange(event, &target_file_affected, &update_watches);
}
if ((updates[i].fflags & NOTE_WRITE) && !target_file_affected) {
HandleCreateItemChange(event, &target_file_affected, &update_watches);
}
send_notification |= target_file_affected;
}
if (update_watches) {
if (!UpdateWatches(&send_notification)) {
delegate_->OnFilePathError(target_);
Cancel();
}
}
if (send_notification) {
delegate_->OnFilePathChanged(target_);
}
}
void FilePathWatcherImpl::OnFileCanWriteWithoutBlocking(int fd) {
NOTREACHED();
}
void FilePathWatcherImpl::WillDestroyCurrentMessageLoop() {
CancelOnMessageLoopThread();
}
bool FilePathWatcherImpl::Watch(const FilePath& path,
FilePathWatcher::Delegate* delegate) {
DCHECK(MessageLoopForIO::current());
DCHECK(target_.value().empty()); // Can only watch one path.
DCHECK(delegate);
DCHECK_EQ(kqueue_, -1);
delegate_ = delegate;
target_ = path;
MessageLoop::current()->AddDestructionObserver(this);
io_message_loop_ = base::MessageLoopProxy::CreateForCurrentThread();
kqueue_ = kqueue();
if (kqueue_ == -1) {
PLOG(ERROR) << "kqueue";
return false;
}
int last_entry = EventsForPath(target_, &events_);
CHECK_NE(last_entry, 0);
EventVector responses(last_entry);
int count = HANDLE_EINTR(kevent(kqueue_, &events_[0], last_entry,
&responses[0], last_entry, NULL));
if (!AreKeventValuesValid(&responses[0], count)) {
// Calling Cancel() here to close any file descriptors that were opened.
// This would happen in the destructor anyways, but FilePathWatchers tend to
// be long lived, and if an error has occurred, there is no reason to waste
// the file descriptors.
Cancel();
return false;
}
return MessageLoopForIO::current()->WatchFileDescriptor(
kqueue_, true, MessageLoopForIO::WATCH_READ, &kqueue_watcher_, this);
}
void FilePathWatcherImpl::Cancel() {
base::MessageLoopProxy* proxy = io_message_loop_.get();
if (!proxy) {
set_cancelled();
return;
}
if (!proxy->BelongsToCurrentThread()) {
proxy->PostTask(FROM_HERE,
NewRunnableMethod(this, &FilePathWatcherImpl::Cancel));
return;
}
CancelOnMessageLoopThread();
}
void FilePathWatcherImpl::CancelOnMessageLoopThread() {
DCHECK(MessageLoopForIO::current());
if (!is_cancelled()) {
set_cancelled();
kqueue_watcher_.StopWatchingFileDescriptor();
CloseFileDescriptor(&kqueue_);
std::for_each(events_.begin(), events_.end(), ReleaseEvent);
events_.clear();
io_message_loop_ = NULL;
MessageLoop::current()->RemoveDestructionObserver(this);
delegate_ = NULL;
}
}
} // namespace
FilePathWatcher::FilePathWatcher() {
impl_ = new FilePathWatcherImpl();
}
} // namespace files
} // namespace base