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inotify_linux.go
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inotify_linux.go
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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.
/*
Package inotify implements a wrapper for the Linux inotify system.
Example:
watcher, err := inotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
err = watcher.Watch("/tmp")
if err != nil {
log.Fatal(err)
}
for {
select {
case ev := <-watcher.Event:
log.Println("event:", ev)
case err := <-watcher.Error:
log.Println("error:", err)
}
}
*/
package inotify // import "golang.org/x/exp/inotify"
import (
"errors"
"fmt"
"os"
"strings"
"sync"
"syscall"
"unsafe"
)
type Event struct {
Mask uint32 // Mask of events
Cookie uint32 // Unique cookie associating related events (for rename(2))
Name string // File name (optional)
}
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
fd int // File descriptor (as returned by the inotify_init() syscall)
watches map[string]*watch // Map of inotify watches (key: path)
paths map[int]string // Map of watched paths (key: watch descriptor)
Error chan error // Errors are sent on this channel
Event chan *Event // 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),
paths: make(map[int]string),
Event: make(chan *Event),
Error: make(chan error),
done: make(chan bool, 1),
}
go w.readEvents()
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
// Send "quit" message to the reader goroutine
w.done <- true
for path := range w.watches {
w.RemoveWatch(path)
}
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 := w.watches[path]
if found {
watchEntry.flags |= flags
flags |= syscall.IN_MASK_ADD
}
w.mu.Lock() // synchronize with readEvents goroutine
wd, err := syscall.InotifyAddWatch(w.fd, path, flags)
if err != nil {
w.mu.Unlock()
return &os.PathError{
Op: "inotify_add_watch",
Path: path,
Err: err,
}
}
if !found {
w.watches[path] = &watch{wd: uint32(wd), flags: flags}
w.paths[wd] = path
}
w.mu.Unlock()
return nil
}
// Watch adds path to the watched file set, watching all events.
func (w *Watcher) Watch(path string) error {
return w.AddWatch(path, IN_ALL_EVENTS)
}
// RemoveWatch removes path from the watched file set.
func (w *Watcher) RemoveWatch(path string) error {
watch, ok := w.watches[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(w.watches, 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
for {
n, err := syscall.Read(w.fd, buf[:])
// See if there is a message on the "done" channel
var done bool
select {
case done = <-w.done:
default:
}
// If EOF or a "done" message is received
if n == 0 || done {
// The syscall.Close can be slow. Close
// w.Event first.
close(w.Event)
err := syscall.Close(w.fd)
if err != nil {
w.Error <- os.NewSyscallError("close", err)
}
close(w.Error)
return
}
if n < 0 {
w.Error <- os.NewSyscallError("read", err)
continue
}
if n < syscall.SizeofInotifyEvent {
w.Error <- errors.New("inotify: short read in readEvents()")
continue
}
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(Event)
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.
w.mu.Lock()
event.Name = w.paths[int(raw.Wd)]
w.mu.Unlock()
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 event on the events channel
w.Event <- event
// Move to the next event in the buffer
offset += syscall.SizeofInotifyEvent + nameLen
}
}
}
// String formats the event e in the form
// "filename: 0xEventMask = IN_ACCESS|IN_ATTRIB_|..."
func (e *Event) String() string {
var events string = ""
m := e.Mask
for _, b := range eventBits {
if m&b.Value == b.Value {
m &^= b.Value
events += "|" + b.Name
}
}
if m != 0 {
events += fmt.Sprintf("|%#x", m)
}
if len(events) > 0 {
events = " == " + events[1:]
}
return fmt.Sprintf("%q: %#x%s", e.Name, e.Mask, events)
}
const (
// Options for inotify_init() are not exported
// IN_CLOEXEC uint32 = syscall.IN_CLOEXEC
// IN_NONBLOCK uint32 = syscall.IN_NONBLOCK
// Options for AddWatch
IN_DONT_FOLLOW uint32 = syscall.IN_DONT_FOLLOW
IN_ONESHOT uint32 = syscall.IN_ONESHOT
IN_ONLYDIR uint32 = syscall.IN_ONLYDIR
// The "IN_MASK_ADD" option is not exported, as AddWatch
// adds it automatically, if there is already a watch for the given path
// IN_MASK_ADD uint32 = syscall.IN_MASK_ADD
// Events
IN_ACCESS uint32 = syscall.IN_ACCESS
IN_ALL_EVENTS uint32 = syscall.IN_ALL_EVENTS
IN_ATTRIB uint32 = syscall.IN_ATTRIB
IN_CLOSE uint32 = syscall.IN_CLOSE
IN_CLOSE_NOWRITE uint32 = syscall.IN_CLOSE_NOWRITE
IN_CLOSE_WRITE uint32 = syscall.IN_CLOSE_WRITE
IN_CREATE uint32 = syscall.IN_CREATE
IN_DELETE uint32 = syscall.IN_DELETE
IN_DELETE_SELF uint32 = syscall.IN_DELETE_SELF
IN_MODIFY uint32 = syscall.IN_MODIFY
IN_MOVE uint32 = syscall.IN_MOVE
IN_MOVED_FROM uint32 = syscall.IN_MOVED_FROM
IN_MOVED_TO uint32 = syscall.IN_MOVED_TO
IN_MOVE_SELF uint32 = syscall.IN_MOVE_SELF
IN_OPEN uint32 = syscall.IN_OPEN
// Special events
IN_ISDIR uint32 = syscall.IN_ISDIR
IN_IGNORED uint32 = syscall.IN_IGNORED
IN_Q_OVERFLOW uint32 = syscall.IN_Q_OVERFLOW
IN_UNMOUNT uint32 = syscall.IN_UNMOUNT
)
var eventBits = []struct {
Value uint32
Name string
}{
{IN_ACCESS, "IN_ACCESS"},
{IN_ATTRIB, "IN_ATTRIB"},
{IN_CLOSE, "IN_CLOSE"},
{IN_CLOSE_NOWRITE, "IN_CLOSE_NOWRITE"},
{IN_CLOSE_WRITE, "IN_CLOSE_WRITE"},
{IN_CREATE, "IN_CREATE"},
{IN_DELETE, "IN_DELETE"},
{IN_DELETE_SELF, "IN_DELETE_SELF"},
{IN_MODIFY, "IN_MODIFY"},
{IN_MOVE, "IN_MOVE"},
{IN_MOVED_FROM, "IN_MOVED_FROM"},
{IN_MOVED_TO, "IN_MOVED_TO"},
{IN_MOVE_SELF, "IN_MOVE_SELF"},
{IN_OPEN, "IN_OPEN"},
{IN_ISDIR, "IN_ISDIR"},
{IN_IGNORED, "IN_IGNORED"},
{IN_Q_OVERFLOW, "IN_Q_OVERFLOW"},
{IN_UNMOUNT, "IN_UNMOUNT"},
}