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watcher_inotify.go
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watcher_inotify.go
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// Copyright (c) 2014-2015 The Notify Authors. All rights reserved.
// Use of this source code is governed by the MIT license that can be
// found in the LICENSE file.
// +build linux
package notify
import (
"bytes"
"errors"
"path/filepath"
"runtime"
"sync"
"sync/atomic"
"syscall"
"unsafe"
)
// eventBufferSize defines the size of the buffer given to read(2) function. One
// should not depend on this value, since it was arbitrary chosen and may be
// changed in the future.
const eventBufferSize = 64 * (syscall.SizeofInotifyEvent + syscall.PathMax + 1)
// consumersCount defines the number of consumers in producer-consumer based
// implementation. Each consumer is run in a separate goroutine and has read
// access to watched files map.
const consumersCount = 2
const invalidDescriptor = -1
// watched is a pair of file path and inotify mask used as a value in
// watched files map.
type watched struct {
path string
mask uint32
}
// inotify implements Watcher interface.
type inotify struct {
sync.RWMutex // protects inotify.m map
m map[int32]*watched // watch descriptor to watched object
fd int32 // inotify file descriptor
pipefd []int // pipe's read and write descriptors
epfd int // epoll descriptor
epes []syscall.EpollEvent // epoll events
buffer [eventBufferSize]byte // inotify event buffer
wg sync.WaitGroup // wait group used to close main loop
c chan<- EventInfo // event dispatcher channel
}
// NewWatcher creates new non-recursive inotify backed by inotify.
func newWatcher(c chan<- EventInfo) watcher {
i := &inotify{
m: make(map[int32]*watched),
fd: invalidDescriptor,
pipefd: []int{invalidDescriptor, invalidDescriptor},
epfd: invalidDescriptor,
epes: make([]syscall.EpollEvent, 0),
c: c,
}
runtime.SetFinalizer(i, func(i *inotify) {
i.epollclose()
if i.fd != invalidDescriptor {
syscall.Close(int(i.fd))
}
})
return i
}
// Watch implements notify.watcher interface.
func (i *inotify) Watch(path string, e Event) error {
return i.watch(path, e)
}
// Rewatch implements notify.watcher interface.
func (i *inotify) Rewatch(path string, _, newevent Event) error {
return i.watch(path, newevent)
}
// watch adds a new watcher to the set of watched objects or modifies the existing
// one. If called for the first time, this function initializes inotify filesystem
// monitor and starts producer-consumers goroutines.
func (i *inotify) watch(path string, e Event) (err error) {
if e&^(All|Event(syscall.IN_ALL_EVENTS)) != 0 {
return errors.New("notify: unknown event")
}
if err = i.lazyinit(); err != nil {
return
}
iwd, err := syscall.InotifyAddWatch(int(i.fd), path, encode(e))
if err != nil {
return
}
i.RLock()
wd := i.m[int32(iwd)]
i.RUnlock()
if wd == nil {
i.Lock()
if i.m[int32(iwd)] == nil {
i.m[int32(iwd)] = &watched{path: path, mask: uint32(e)}
}
i.Unlock()
} else {
i.Lock()
wd.mask = uint32(e)
i.Unlock()
}
return nil
}
// lazyinit sets up all required file descriptors and starts 1+consumersCount
// goroutines. The producer goroutine blocks until file-system notifications
// occur. Then, all events are read from system buffer and sent to consumer
// goroutines which construct valid notify events. This method uses
// Double-Checked Locking optimization.
func (i *inotify) lazyinit() error {
if atomic.LoadInt32(&i.fd) == invalidDescriptor {
i.Lock()
defer i.Unlock()
if atomic.LoadInt32(&i.fd) == invalidDescriptor {
fd, err := syscall.InotifyInit()
if err != nil {
return err
}
i.fd = int32(fd)
if err = i.epollinit(); err != nil {
_, _ = i.epollclose(), syscall.Close(int(fd)) // Ignore errors.
i.fd = invalidDescriptor
return err
}
esch := make(chan []*event)
go i.loop(esch)
i.wg.Add(consumersCount)
for n := 0; n < consumersCount; n++ {
go i.send(esch)
}
}
}
return nil
}
// epollinit opens an epoll file descriptor and creates a pipe which will be
// used to wake up the epoll_wait(2) function. Then, file descriptor associated
// with inotify event queue and the read end of the pipe are added to epoll set.
// Note that `fd` member must be set before this function is called.
func (i *inotify) epollinit() (err error) {
if i.epfd, err = syscall.EpollCreate1(0); err != nil {
return
}
if err = syscall.Pipe(i.pipefd); err != nil {
return
}
i.epes = []syscall.EpollEvent{
{Events: syscall.EPOLLIN, Fd: i.fd},
{Events: syscall.EPOLLIN, Fd: int32(i.pipefd[0])},
}
if err = syscall.EpollCtl(i.epfd, syscall.EPOLL_CTL_ADD, int(i.fd), &i.epes[0]); err != nil {
return
}
return syscall.EpollCtl(i.epfd, syscall.EPOLL_CTL_ADD, i.pipefd[0], &i.epes[1])
}
// epollclose closes the file descriptor created by the call to epoll_create(2)
// and two file descriptors opened by pipe(2) function.
func (i *inotify) epollclose() (err error) {
if i.epfd != invalidDescriptor {
if err = syscall.Close(i.epfd); err == nil {
i.epfd = invalidDescriptor
}
}
for n, fd := range i.pipefd {
if fd != invalidDescriptor {
switch e := syscall.Close(fd); {
case e != nil && err == nil:
err = e
case e == nil:
i.pipefd[n] = invalidDescriptor
}
}
}
return
}
// loop blocks until either inotify or pipe file descriptor is ready for I/O.
// All read operations triggered by filesystem notifications are forwarded to
// one of the event's consumers. If pipe fd became ready, loop function closes
// all file descriptors opened by lazyinit method and returns afterwards.
func (i *inotify) loop(esch chan<- []*event) {
epes := make([]syscall.EpollEvent, 1)
fd := atomic.LoadInt32(&i.fd)
for {
switch _, err := syscall.EpollWait(i.epfd, epes, -1); err {
case nil:
switch epes[0].Fd {
case fd:
esch <- i.read()
epes[0].Fd = 0
case int32(i.pipefd[0]):
i.Lock()
defer i.Unlock()
if err = syscall.Close(int(fd)); err != nil && err != syscall.EINTR {
panic("notify: close(2) error " + err.Error())
}
atomic.StoreInt32(&i.fd, invalidDescriptor)
if err = i.epollclose(); err != nil && err != syscall.EINTR {
panic("notify: epollclose error " + err.Error())
}
close(esch)
return
}
case syscall.EINTR:
continue
default: // We should never reach this line.
panic("notify: epoll_wait(2) error " + err.Error())
}
}
}
// read reads events from an inotify file descriptor. It does not handle errors
// returned from read(2) function since they are not critical to watcher logic.
func (i *inotify) read() (es []*event) {
n, err := syscall.Read(int(i.fd), i.buffer[:])
if err != nil || n < syscall.SizeofInotifyEvent {
return
}
var sys *syscall.InotifyEvent
nmin := n - syscall.SizeofInotifyEvent
for pos, path := 0, ""; pos <= nmin; {
sys = (*syscall.InotifyEvent)(unsafe.Pointer(&i.buffer[pos]))
pos += syscall.SizeofInotifyEvent
if path = ""; sys.Len > 0 {
endpos := pos + int(sys.Len)
path = string(bytes.TrimRight(i.buffer[pos:endpos], "\x00"))
pos = endpos
}
es = append(es, &event{
sys: syscall.InotifyEvent{
Wd: sys.Wd,
Mask: sys.Mask,
Cookie: sys.Cookie,
},
path: path,
})
}
return
}
// send is a consumer function which sends events to event dispatcher channel.
// It is run in a separate goroutine in order to not block loop method when
// possibly expensive write operations are performed on inotify map.
func (i *inotify) send(esch <-chan []*event) {
for es := range esch {
for _, e := range i.transform(es) {
if e != nil {
i.c <- e
}
}
}
i.wg.Done()
}
// transform prepares events read from inotify file descriptor for sending to
// user. It removes invalid events and these which are no longer present in
// inotify map. This method may also split one raw event into two different ones
// when system-dependent result is required.
func (i *inotify) transform(es []*event) []*event {
var multi []*event
i.RLock()
for idx, e := range es {
if e.sys.Mask&(syscall.IN_IGNORED|syscall.IN_Q_OVERFLOW) != 0 {
es[idx] = nil
continue
}
wd, ok := i.m[e.sys.Wd]
if !ok || e.sys.Mask&encode(Event(wd.mask)) == 0 {
es[idx] = nil
continue
}
if e.path == "" {
e.path = wd.path
} else {
e.path = filepath.Join(wd.path, e.path)
}
multi = append(multi, decode(Event(wd.mask), e))
if e.event == 0 {
es[idx] = nil
}
}
i.RUnlock()
es = append(es, multi...)
return es
}
// encode converts notify system-independent events to valid inotify mask
// which can be passed to inotify_add_watch(2) function.
func encode(e Event) uint32 {
if e&Create != 0 {
e = (e ^ Create) | InCreate | InMovedTo
}
if e&Remove != 0 {
e = (e ^ Remove) | InDelete | InDeleteSelf
}
if e&Write != 0 {
e = (e ^ Write) | InModify
}
if e&Rename != 0 {
e = (e ^ Rename) | InMovedFrom | InMoveSelf
}
return uint32(e)
}
// decode uses internally stored mask to distinguish whether system-independent
// or system-dependent event is requested. The first one is created by modifying
// `e` argument. decode method sets e.event value to 0 when an event should be
// skipped. System-dependent event is set as the function's return value which
// can be nil when the event should not be passed on.
func decode(mask Event, e *event) (syse *event) {
if sysmask := uint32(mask) & e.sys.Mask; sysmask != 0 {
syse = &event{sys: syscall.InotifyEvent{
Wd: e.sys.Wd,
Mask: e.sys.Mask,
Cookie: e.sys.Cookie,
}, event: Event(sysmask), path: e.path}
}
imask := encode(mask)
switch {
case mask&Create != 0 && imask&uint32(InCreate|InMovedTo)&e.sys.Mask != 0:
e.event = Create
case mask&Remove != 0 && imask&uint32(InDelete|InDeleteSelf)&e.sys.Mask != 0:
e.event = Remove
case mask&Write != 0 && imask&uint32(InModify)&e.sys.Mask != 0:
e.event = Write
case mask&Rename != 0 && imask&uint32(InMovedFrom|InMoveSelf)&e.sys.Mask != 0:
e.event = Rename
default:
e.event = 0
}
return
}
// Unwatch implements notify.watcher interface. It looks for watch descriptor
// related to registered path and if found, calls inotify_rm_watch(2) function.
// This method is allowed to return EINVAL error when concurrently requested to
// delete identical path.
func (i *inotify) Unwatch(path string) (err error) {
iwd := int32(invalidDescriptor)
i.RLock()
for iwdkey, wd := range i.m {
if wd.path == path {
iwd = iwdkey
break
}
}
i.RUnlock()
if iwd == invalidDescriptor {
return errors.New("notify: path " + path + " is already watched")
}
fd := atomic.LoadInt32(&i.fd)
if _, err = syscall.InotifyRmWatch(int(fd), uint32(iwd)); err != nil {
return
}
i.Lock()
delete(i.m, iwd)
i.Unlock()
return nil
}
// Close implements notify.watcher interface. It removes all existing watch
// descriptors and wakes up producer goroutine by sending data to the write end
// of the pipe. The function waits for a signal from producer which means that
// all operations on current monitoring instance are done.
func (i *inotify) Close() (err error) {
i.Lock()
if fd := atomic.LoadInt32(&i.fd); fd == invalidDescriptor {
i.Unlock()
return nil
}
for iwd := range i.m {
if _, e := syscall.InotifyRmWatch(int(i.fd), uint32(iwd)); e != nil && err == nil {
err = e
}
delete(i.m, iwd)
}
switch _, errwrite := syscall.Write(i.pipefd[1], []byte{0x00}); {
case errwrite != nil && err == nil:
err = errwrite
fallthrough
case errwrite != nil:
i.Unlock()
default:
i.Unlock()
i.wg.Wait()
}
return
}