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// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build linux
package fsnotify
import (
// Watcher watches a set of files, delivering events to a channel.
type Watcher struct {
Events chan Event
Errors chan error
mu sync.Mutex // Map access
cv *sync.Cond // sync removing on rm_watch with IN_IGNORE
fd int
poller *fdPoller
watches map[string]*watch // Map of inotify watches (key: path)
paths map[int]string // Map of watched paths (key: watch descriptor)
done chan struct{} // Channel for sending a "quit message" to the reader goroutine
doneResp chan struct{} // Channel to respond to Close
// NewWatcher establishes a new watcher with the underlying OS and begins waiting for events.
func NewWatcher() (*Watcher, error) {
// Create inotify fd
fd, errno := unix.InotifyInit1(unix.IN_CLOEXEC)
if fd == -1 {
return nil, errno
// Create epoll
poller, err := newFdPoller(fd)
if err != nil {
return nil, err
w := &Watcher{
fd: fd,
poller: poller,
watches: make(map[string]*watch),
paths: make(map[int]string),
Events: make(chan Event),
Errors: make(chan error),
done: make(chan struct{}),
doneResp: make(chan struct{}),
} = sync.NewCond(&
go w.readEvents()
return w, nil
func (w *Watcher) isClosed() bool {
select {
case <-w.done:
return true
return false
// Close removes all watches and closes the events channel.
func (w *Watcher) Close() error {
if w.isClosed() {
return nil
// Send 'close' signal to goroutine, and set the Watcher to closed.
// Wake up goroutine
// Wait for goroutine to close
return nil
// Add starts watching the named file or directory (non-recursively).
func (w *Watcher) Add(name string) error {
name = filepath.Clean(name)
if w.isClosed() {
return errors.New("inotify instance already closed")
const agnosticEvents = unix.IN_MOVED_TO | unix.IN_MOVED_FROM |
unix.IN_CREATE | unix.IN_ATTRIB | unix.IN_MODIFY |
var flags uint32 = agnosticEvents
watchEntry, found :=[name]
if found {
watchEntry.flags |= flags
flags |= unix.IN_MASK_ADD
wd, errno := unix.InotifyAddWatch(w.fd, name, flags)
if wd == -1 {
return errno
}[name] = &watch{wd: uint32(wd), flags: flags}
w.paths[wd] = name
return nil
// Remove stops watching the named file or directory (non-recursively).
func (w *Watcher) Remove(name string) error {
name = filepath.Clean(name)
// Fetch the watch.
watch, ok :=[name]
// Remove it from inotify.
if !ok {
return fmt.Errorf("can't remove non-existent inotify watch for: %s", name)
// inotify_rm_watch will return EINVAL if the file has been deleted;
// the inotify will already have been removed.
// watches and pathes are deleted in ignoreLinux() implicitly and asynchronously
// by calling inotify_rm_watch() below. e.g. readEvents() goroutine receives IN_IGNORE
// so that EINVAL means that the wd is being rm_watch()ed or its file removed
// by another thread and we have not received IN_IGNORE event.
success, errno := unix.InotifyRmWatch(w.fd, watch.wd)
if success == -1 {
// TODO: Perhaps it's not helpful to return an error here in every case.
// the only two possible errors are:
// EBADF, which happens when w.fd is not a valid file descriptor of any kind.
// EINVAL, which is when fd is not an inotify descriptor or wd is not a valid watch descriptor.
// Watch descriptors are invalidated when they are removed explicitly or implicitly;
// explicitly by inotify_rm_watch, implicitly when the file they are watching is deleted.
return errno
// wait until ignoreLinux() deleting maps
exists := true
for exists {
_, exists =[name]
return nil
type watch struct {
wd uint32 // Watch descriptor (as returned by the inotify_add_watch() syscall)
flags uint32 // inotify flags of this watch (see inotify(7) for the list of valid flags)
// readEvents reads from the inotify file descriptor, converts the
// received events into Event objects and sends them via the Events channel
func (w *Watcher) readEvents() {
var (
buf [unix.SizeofInotifyEvent * 4096]byte // Buffer for a maximum of 4096 raw events
n int // Number of bytes read with read()
errno error // Syscall errno
ok bool // For poller.wait
defer close(w.doneResp)
defer close(w.Errors)
defer close(w.Events)
defer unix.Close(w.fd)
defer w.poller.close()
for {
// See if we have been closed.
if w.isClosed() {
ok, errno = w.poller.wait()
if errno != nil {
select {
case w.Errors <- errno:
case <-w.done:
if !ok {
n, errno = unix.Read(w.fd, buf[:])
// If a signal interrupted execution, see if we've been asked to close, and try again.
// :
// "Before Linux 3.8, reads from an inotify(7) file descriptor were not restartable"
if errno == unix.EINTR {
// unix.Read might have been woken up by Close. If so, we're done.
if w.isClosed() {
if n < unix.SizeofInotifyEvent {
var err error
if n == 0 {
// If EOF is received. This should really never happen.
err = io.EOF
} else if n < 0 {
// If an error occurred while reading.
err = errno
} else {
// Read was too short.
err = errors.New("notify: short read in readEvents()")
select {
case w.Errors <- err:
case <-w.done:
var offset uint32
// We don't know how many events we just read into the buffer
// While the offset points to at least one whole event...
for offset <= uint32(n-unix.SizeofInotifyEvent) {
// Point "raw" to the event in the buffer
raw := (*unix.InotifyEvent)(unsafe.Pointer(&buf[offset]))
mask := uint32(raw.Mask)
nameLen := uint32(raw.Len)
if mask&unix.IN_Q_OVERFLOW != 0 {
select {
case w.Errors <- ErrEventOverflow:
case <-w.done:
// If the event happened to the watched directory or the watched file, the kernel
// doesn't append the filename to the event, but we would like to always fill the
// the "Name" field with a valid filename. We retrieve the path of the watch from
// the "paths" map.
name := w.paths[int(raw.Wd)]
if nameLen > 0 {
// Point "bytes" at the first byte of the filename
bytes := (*[unix.PathMax]byte)(unsafe.Pointer(&buf[offset+unix.SizeofInotifyEvent]))
// The filename is padded with NULL bytes. TrimRight() gets rid of those.
name += "/" + strings.TrimRight(string(bytes[0:nameLen]), "\000")
event := newEvent(name, mask)
// Send the events that are not ignored on the events channel
if !event.ignoreLinux(w, raw.Wd, mask) {
select {
case w.Events <- event:
case <-w.done:
// Move to the next event in the buffer
offset += unix.SizeofInotifyEvent + nameLen
// Certain types of events can be "ignored" and not sent over the Events
// channel. Such as events marked ignore by the kernel, or MODIFY events
// against files that do not exist.
func (e *Event) ignoreLinux(w *Watcher, wd int32, mask uint32) bool {
// Ignore anything the inotify API says to ignore
if mask&unix.IN_IGNORED == unix.IN_IGNORED {
name := w.paths[int(wd)]
delete(w.paths, int(wd))
delete(, name)
return true
// If the event is not a DELETE or RENAME, the file must exist.
// Otherwise the event is ignored.
// *Note*: this was put in place because it was seen that a MODIFY
// event was sent after the DELETE. This ignores that MODIFY and
// assumes a DELETE will come or has come if the file doesn't exist.
if !(e.Op&Remove == Remove || e.Op&Rename == Rename) {
_, statErr := os.Lstat(e.Name)
return os.IsNotExist(statErr)
return false
// newEvent returns an platform-independent Event based on an inotify mask.
func newEvent(name string, mask uint32) Event {
e := Event{Name: name}
if mask&unix.IN_CREATE == unix.IN_CREATE || mask&unix.IN_MOVED_TO == unix.IN_MOVED_TO {
e.Op |= Create
if mask&unix.IN_DELETE_SELF == unix.IN_DELETE_SELF || mask&unix.IN_DELETE == unix.IN_DELETE {
e.Op |= Remove
if mask&unix.IN_MODIFY == unix.IN_MODIFY {
e.Op |= Write
if mask&unix.IN_MOVE_SELF == unix.IN_MOVE_SELF || mask&unix.IN_MOVED_FROM == unix.IN_MOVED_FROM {
e.Op |= Rename
if mask&unix.IN_ATTRIB == unix.IN_ATTRIB {
e.Op |= Chmod
return e