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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 (
const (
// Options for inotify_init() are not exported
// sys_IN_CLOEXEC uint32 = syscall.IN_CLOEXEC
// sys_IN_NONBLOCK uint32 = syscall.IN_NONBLOCK
// Options for AddWatch
sys_IN_DONT_FOLLOW uint32 = syscall.IN_DONT_FOLLOW
sys_IN_ONESHOT uint32 = syscall.IN_ONESHOT
sys_IN_ONLYDIR uint32 = syscall.IN_ONLYDIR
// The "sys_IN_MASK_ADD" option is not exported, as AddWatch
// adds it automatically, if there is already a watch for the given path
// sys_IN_MASK_ADD uint32 = syscall.IN_MASK_ADD
// Events
sys_IN_ACCESS uint32 = syscall.IN_ACCESS
sys_IN_ALL_EVENTS uint32 = syscall.IN_ALL_EVENTS
sys_IN_ATTRIB uint32 = syscall.IN_ATTRIB
sys_IN_CLOSE uint32 = syscall.IN_CLOSE
sys_IN_CLOSE_WRITE uint32 = syscall.IN_CLOSE_WRITE
sys_IN_CREATE uint32 = syscall.IN_CREATE
sys_IN_DELETE uint32 = syscall.IN_DELETE
sys_IN_DELETE_SELF uint32 = syscall.IN_DELETE_SELF
sys_IN_MODIFY uint32 = syscall.IN_MODIFY
sys_IN_MOVE uint32 = syscall.IN_MOVE
sys_IN_MOVED_FROM uint32 = syscall.IN_MOVED_FROM
sys_IN_MOVED_TO uint32 = syscall.IN_MOVED_TO
sys_IN_MOVE_SELF uint32 = syscall.IN_MOVE_SELF
sys_IN_OPEN uint32 = syscall.IN_OPEN
// Special events
sys_IN_ISDIR uint32 = syscall.IN_ISDIR
sys_IN_IGNORED uint32 = syscall.IN_IGNORED
sys_IN_Q_OVERFLOW uint32 = syscall.IN_Q_OVERFLOW
sys_IN_UNMOUNT uint32 = syscall.IN_UNMOUNT
type FileEvent struct {
mask uint32 // Mask of events
cookie uint32 // Unique cookie associating related events (for rename(2))
Name string // File name (optional)
// IsCreate reports whether the FileEvent was triggered by a creation
func (e *FileEvent) IsCreate() bool {
return (e.mask&sys_IN_CREATE) == sys_IN_CREATE || (e.mask&sys_IN_MOVED_TO) == sys_IN_MOVED_TO
// IsDelete reports whether the FileEvent was triggered by a delete
func (e *FileEvent) IsDelete() bool {
return (e.mask&sys_IN_DELETE_SELF) == sys_IN_DELETE_SELF || (e.mask&sys_IN_DELETE) == sys_IN_DELETE
// IsModify reports whether the FileEvent was triggered by a file modification or attribute change
func (e *FileEvent) IsModify() bool {
return ((e.mask&sys_IN_MODIFY) == sys_IN_MODIFY || (e.mask&sys_IN_ATTRIB) == sys_IN_ATTRIB)
// IsRename reports whether the FileEvent was triggered by a change name
func (e *FileEvent) IsRename() bool {
return ((e.mask&sys_IN_MOVE_SELF) == sys_IN_MOVE_SELF || (e.mask&sys_IN_MOVED_FROM) == sys_IN_MOVED_FROM)
// IsAttrib reports whether the FileEvent was triggered by a change in the file metadata.
func (e *FileEvent) IsAttrib() bool {
return (e.mask & sys_IN_ATTRIB) == sys_IN_ATTRIB
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)
type Watcher struct {
mu sync.Mutex // Map access
fd int // File descriptor (as returned by the inotify_init() syscall)
watches map[string]*watch // Map of inotify watches (key: path)
fsnFlags map[string]uint32 // Map of watched files to flags used for filter
fsnmut sync.Mutex // Protects access to fsnFlags.
paths map[int]string // Map of watched paths (key: watch descriptor)
Error chan error // Errors are sent on this channel
internalEvent chan *FileEvent // Events are queued on this channel
Event chan *FileEvent // Events are returned on this channel
done chan bool // Channel for sending a "quit message" to the reader goroutine
isClosed bool // Set to true when Close() is first called
// NewWatcher creates and returns a new inotify instance using inotify_init(2)
func NewWatcher() (*Watcher, error) {
fd, errno := syscall.InotifyInit()
if fd == -1 {
return nil, os.NewSyscallError("inotify_init", errno)
w := &Watcher{
fd: fd,
watches: make(map[string]*watch),
fsnFlags: make(map[string]uint32),
paths: make(map[int]string),
internalEvent: make(chan *FileEvent),
Event: make(chan *FileEvent),
Error: make(chan error),
done: make(chan bool, 1),
go w.readEvents()
go w.purgeEvents()
return w, nil
// Close closes an inotify watcher instance
// It sends a message to the reader goroutine to quit and removes all watches
// associated with the inotify instance
func (w *Watcher) Close() error {
if w.isClosed {
return nil
w.isClosed = true
// Remove all watches
for path := range {
// Send "quit" message to the reader goroutine
w.done <- true
return nil
// AddWatch adds path to the watched file set.
// The flags are interpreted as described in inotify_add_watch(2).
func (w *Watcher) addWatch(path string, flags uint32) error {
if w.isClosed {
return errors.New("inotify instance already closed")
watchEntry, found :=[path]
if found {
watchEntry.flags |= flags
flags |= syscall.IN_MASK_ADD
wd, errno := syscall.InotifyAddWatch(w.fd, path, flags)
if wd == -1 {
return errno
}[path] = &watch{wd: uint32(wd), flags: flags}
w.paths[wd] = path
return nil
// Watch adds path to the watched file set, watching all events.
func (w *Watcher) watch(path string) error {
return w.addWatch(path, sys_AGNOSTIC_EVENTS)
// RemoveWatch removes path from the watched file set.
func (w *Watcher) removeWatch(path string) error {
watch, ok :=[path]
if !ok {
return errors.New(fmt.Sprintf("can't remove non-existent inotify watch for: %s", path))
success, errno := syscall.InotifyRmWatch(w.fd, watch.wd)
if success == -1 {
return os.NewSyscallError("inotify_rm_watch", errno)
delete(, path)
return nil
// readEvents reads from the inotify file descriptor, converts the
// received events into Event objects and sends them via the Event channel
func (w *Watcher) readEvents() {
var (
buf [syscall.SizeofInotifyEvent * 4096]byte // Buffer for a maximum of 4096 raw events
n int // Number of bytes read with read()
errno error // Syscall errno
for {
// See if there is a message on the "done" channel
select {
case <-w.done:
n, errno = syscall.Read(w.fd, buf[:])
// If EOF is received
if n == 0 {
if n < 0 {
w.Error <- os.NewSyscallError("read", errno)
if n < syscall.SizeofInotifyEvent {
w.Error <- errors.New("inotify: short read in readEvents()")
var offset uint32 = 0
// 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-syscall.SizeofInotifyEvent) {
// Point "raw" to the event in the buffer
raw := (*syscall.InotifyEvent)(unsafe.Pointer(&buf[offset]))
event := new(FileEvent)
event.mask = uint32(raw.Mask)
event.cookie = uint32(raw.Cookie)
nameLen := uint32(raw.Len)
// 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.
event.Name = w.paths[int(raw.Wd)]
watchedName := event.Name
if nameLen > 0 {
// Point "bytes" at the first byte of the filename
bytes := (*[syscall.PathMax]byte)(unsafe.Pointer(&buf[offset+syscall.SizeofInotifyEvent]))
// The filename is padded with NUL bytes. TrimRight() gets rid of those.
event.Name += "/" + strings.TrimRight(string(bytes[0:nameLen]), "\000")
// Send the events that are not ignored on the events channel
if !event.ignoreLinux() {
// Setup FSNotify flags (inherit from directory watch)
if _, fsnFound := w.fsnFlags[event.Name]; !fsnFound {
if fsnFlags, watchFound := w.fsnFlags[watchedName]; watchFound {
w.fsnFlags[event.Name] = fsnFlags
} else {
w.fsnFlags[event.Name] = FSN_ALL
w.internalEvent <- event
// Move to the next event in the buffer
offset += syscall.SizeofInotifyEvent + nameLen
// Certain types of events can be "ignored" and not sent over the Event
// channel. Such as events marked ignore by the kernel, or MODIFY events
// against files that do not exist.
func (e *FileEvent) ignoreLinux() bool {
// Ignore anything the inotify API says to ignore
if e.mask&sys_IN_IGNORED == sys_IN_IGNORED {
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.IsDelete() || e.IsRename()) {
_, statErr := os.Lstat(e.Name)
return os.IsNotExist(statErr)
return false