github.com/Hellyna/notify@v0.0.0-20210101060149-8ebdd4ef22cf/watcher_inotify.go (about) 1 // Copyright (c) 2014-2015 The Notify Authors. All rights reserved. 2 // Use of this source code is governed by the MIT license that can be 3 // found in the LICENSE file. 4 5 // +build linux 6 7 package notify 8 9 import ( 10 "bytes" 11 "errors" 12 "path/filepath" 13 "runtime" 14 "sync" 15 "sync/atomic" 16 "unsafe" 17 18 "golang.org/x/sys/unix" 19 ) 20 21 // eventBufferSize defines the size of the buffer given to read(2) function. One 22 // should not depend on this value, since it was arbitrary chosen and may be 23 // changed in the future. 24 const eventBufferSize = 64 * (unix.SizeofInotifyEvent + unix.PathMax + 1) 25 26 // consumersCount defines the number of consumers in producer-consumer based 27 // implementation. Each consumer is run in a separate goroutine and has read 28 // access to watched files map. 29 const consumersCount = 2 30 31 const invalidDescriptor = -1 32 33 // watched is a pair of file path and inotify mask used as a value in 34 // watched files map. 35 type watched struct { 36 path string 37 mask uint32 38 } 39 40 // inotify implements Watcher interface. 41 type inotify struct { 42 sync.RWMutex // protects inotify.m map 43 m map[int32]*watched // watch descriptor to watched object 44 fd int32 // inotify file descriptor 45 pipefd []int // pipe's read and write descriptors 46 epfd int // epoll descriptor 47 epes []unix.EpollEvent // epoll events 48 buffer [eventBufferSize]byte // inotify event buffer 49 wg sync.WaitGroup // wait group used to close main loop 50 c chan<- EventInfo // event dispatcher channel 51 } 52 53 // NewWatcher creates new non-recursive inotify backed by inotify. 54 func newWatcher(c chan<- EventInfo) watcher { 55 i := &inotify{ 56 m: make(map[int32]*watched), 57 fd: invalidDescriptor, 58 pipefd: []int{invalidDescriptor, invalidDescriptor}, 59 epfd: invalidDescriptor, 60 epes: make([]unix.EpollEvent, 0), 61 c: c, 62 } 63 runtime.SetFinalizer(i, func(i *inotify) { 64 i.epollclose() 65 if i.fd != invalidDescriptor { 66 unix.Close(int(i.fd)) 67 } 68 }) 69 return i 70 } 71 72 // Watch implements notify.watcher interface. 73 func (i *inotify) Watch(path string, e Event) error { 74 return i.watch(path, e) 75 } 76 77 // Rewatch implements notify.watcher interface. 78 func (i *inotify) Rewatch(path string, _, newevent Event) error { 79 return i.watch(path, newevent) 80 } 81 82 // watch adds a new watcher to the set of watched objects or modifies the existing 83 // one. If called for the first time, this function initializes inotify filesystem 84 // monitor and starts producer-consumers goroutines. 85 func (i *inotify) watch(path string, e Event) (err error) { 86 if e&^(All|Event(unix.IN_ALL_EVENTS)) != 0 { 87 return errors.New("notify: unknown event") 88 } 89 if err = i.lazyinit(); err != nil { 90 return 91 } 92 iwd, err := unix.InotifyAddWatch(int(i.fd), path, encode(e)) 93 if err != nil { 94 return 95 } 96 i.Lock() 97 if wd, ok := i.m[int32(iwd)]; !ok { 98 i.m[int32(iwd)] = &watched{path: path, mask: uint32(e)} 99 } else { 100 wd.path = path 101 wd.mask = uint32(e) 102 } 103 i.Unlock() 104 return nil 105 } 106 107 // lazyinit sets up all required file descriptors and starts 1+consumersCount 108 // goroutines. The producer goroutine blocks until file-system notifications 109 // occur. Then, all events are read from system buffer and sent to consumer 110 // goroutines which construct valid notify events. This method uses 111 // Double-Checked Locking optimization. 112 func (i *inotify) lazyinit() error { 113 if atomic.LoadInt32(&i.fd) == invalidDescriptor { 114 i.Lock() 115 defer i.Unlock() 116 if atomic.LoadInt32(&i.fd) == invalidDescriptor { 117 fd, err := unix.InotifyInit1(unix.IN_CLOEXEC) 118 if err != nil { 119 return err 120 } 121 i.fd = int32(fd) 122 if err = i.epollinit(); err != nil { 123 _, _ = i.epollclose(), unix.Close(int(fd)) // Ignore errors. 124 i.fd = invalidDescriptor 125 return err 126 } 127 esch := make(chan []*event) 128 go i.loop(esch) 129 i.wg.Add(consumersCount) 130 for n := 0; n < consumersCount; n++ { 131 go i.send(esch) 132 } 133 } 134 } 135 return nil 136 } 137 138 // epollinit opens an epoll file descriptor and creates a pipe which will be 139 // used to wake up the epoll_wait(2) function. Then, file descriptor associated 140 // with inotify event queue and the read end of the pipe are added to epoll set. 141 // Note that `fd` member must be set before this function is called. 142 func (i *inotify) epollinit() (err error) { 143 if i.epfd, err = unix.EpollCreate1(0); err != nil { 144 return 145 } 146 if err = unix.Pipe(i.pipefd); err != nil { 147 return 148 } 149 i.epes = []unix.EpollEvent{ 150 {Events: unix.EPOLLIN, Fd: i.fd}, 151 {Events: unix.EPOLLIN, Fd: int32(i.pipefd[0])}, 152 } 153 if err = unix.EpollCtl(i.epfd, unix.EPOLL_CTL_ADD, int(i.fd), &i.epes[0]); err != nil { 154 return 155 } 156 return unix.EpollCtl(i.epfd, unix.EPOLL_CTL_ADD, i.pipefd[0], &i.epes[1]) 157 } 158 159 // epollclose closes the file descriptor created by the call to epoll_create(2) 160 // and two file descriptors opened by pipe(2) function. 161 func (i *inotify) epollclose() (err error) { 162 if i.epfd != invalidDescriptor { 163 if err = unix.Close(i.epfd); err == nil { 164 i.epfd = invalidDescriptor 165 } 166 } 167 for n, fd := range i.pipefd { 168 if fd != invalidDescriptor { 169 switch e := unix.Close(fd); { 170 case e != nil && err == nil: 171 err = e 172 case e == nil: 173 i.pipefd[n] = invalidDescriptor 174 } 175 } 176 } 177 return 178 } 179 180 // loop blocks until either inotify or pipe file descriptor is ready for I/O. 181 // All read operations triggered by filesystem notifications are forwarded to 182 // one of the event's consumers. If pipe fd became ready, loop function closes 183 // all file descriptors opened by lazyinit method and returns afterwards. 184 func (i *inotify) loop(esch chan<- []*event) { 185 epes := make([]unix.EpollEvent, 1) 186 fd := atomic.LoadInt32(&i.fd) 187 for { 188 switch _, err := unix.EpollWait(i.epfd, epes, -1); err { 189 case nil: 190 switch epes[0].Fd { 191 case fd: 192 esch <- i.read() 193 epes[0].Fd = 0 194 case int32(i.pipefd[0]): 195 i.Lock() 196 defer i.Unlock() 197 if err = unix.Close(int(fd)); err != nil && err != unix.EINTR { 198 panic("notify: close(2) error " + err.Error()) 199 } 200 atomic.StoreInt32(&i.fd, invalidDescriptor) 201 if err = i.epollclose(); err != nil && err != unix.EINTR { 202 panic("notify: epollclose error " + err.Error()) 203 } 204 close(esch) 205 return 206 } 207 case unix.EINTR: 208 continue 209 default: // We should never reach this line. 210 panic("notify: epoll_wait(2) error " + err.Error()) 211 } 212 } 213 } 214 215 // read reads events from an inotify file descriptor. It does not handle errors 216 // returned from read(2) function since they are not critical to watcher logic. 217 func (i *inotify) read() (es []*event) { 218 n, err := unix.Read(int(i.fd), i.buffer[:]) 219 if err != nil || n < unix.SizeofInotifyEvent { 220 return 221 } 222 var sys *unix.InotifyEvent 223 nmin := n - unix.SizeofInotifyEvent 224 for pos, path := 0, ""; pos <= nmin; { 225 sys = (*unix.InotifyEvent)(unsafe.Pointer(&i.buffer[pos])) 226 pos += unix.SizeofInotifyEvent 227 if path = ""; sys.Len > 0 { 228 endpos := pos + int(sys.Len) 229 path = string(bytes.TrimRight(i.buffer[pos:endpos], "\x00")) 230 pos = endpos 231 } 232 es = append(es, &event{ 233 sys: unix.InotifyEvent{ 234 Wd: sys.Wd, 235 Mask: sys.Mask, 236 Cookie: sys.Cookie, 237 }, 238 path: path, 239 }) 240 } 241 return 242 } 243 244 // send is a consumer function which sends events to event dispatcher channel. 245 // It is run in a separate goroutine in order to not block loop method when 246 // possibly expensive write operations are performed on inotify map. 247 func (i *inotify) send(esch <-chan []*event) { 248 for es := range esch { 249 for _, e := range i.transform(es) { 250 if e != nil { 251 i.c <- e 252 } 253 } 254 } 255 i.wg.Done() 256 } 257 258 // transform prepares events read from inotify file descriptor for sending to 259 // user. It removes invalid events and these which are no longer present in 260 // inotify map. This method may also split one raw event into two different ones 261 // when system-dependent result is required. 262 func (i *inotify) transform(es []*event) []*event { 263 var multi []*event 264 i.RLock() 265 for idx, e := range es { 266 if e.sys.Mask&(unix.IN_IGNORED|unix.IN_Q_OVERFLOW) != 0 { 267 es[idx] = nil 268 continue 269 } 270 wd, ok := i.m[e.sys.Wd] 271 if !ok || e.sys.Mask&encode(Event(wd.mask)) == 0 { 272 es[idx] = nil 273 continue 274 } 275 if e.path == "" { 276 e.path = wd.path 277 } else { 278 e.path = filepath.Join(wd.path, e.path) 279 } 280 multi = append(multi, decode(Event(wd.mask), e)) 281 if e.event == 0 { 282 es[idx] = nil 283 } 284 } 285 i.RUnlock() 286 es = append(es, multi...) 287 return es 288 } 289 290 // encode converts notify system-independent events to valid inotify mask 291 // which can be passed to inotify_add_watch(2) function. 292 func encode(e Event) uint32 { 293 if e&Create != 0 { 294 e = (e ^ Create) | InCreate | InMovedTo 295 } 296 if e&Remove != 0 { 297 e = (e ^ Remove) | InDelete | InDeleteSelf 298 } 299 if e&Write != 0 { 300 e = (e ^ Write) | InModify 301 } 302 if e&Rename != 0 { 303 e = (e ^ Rename) | InMovedFrom | InMoveSelf 304 } 305 return uint32(e) 306 } 307 308 // decode uses internally stored mask to distinguish whether system-independent 309 // or system-dependent event is requested. The first one is created by modifying 310 // `e` argument. decode method sets e.event value to 0 when an event should be 311 // skipped. System-dependent event is set as the function's return value which 312 // can be nil when the event should not be passed on. 313 func decode(mask Event, e *event) (syse *event) { 314 if sysmask := uint32(mask) & e.sys.Mask; sysmask != 0 { 315 syse = &event{sys: unix.InotifyEvent{ 316 Wd: e.sys.Wd, 317 Mask: e.sys.Mask, 318 Cookie: e.sys.Cookie, 319 }, event: Event(sysmask), path: e.path} 320 } 321 imask := encode(mask) 322 switch { 323 case mask&Create != 0 && imask&uint32(InCreate|InMovedTo)&e.sys.Mask != 0: 324 e.event = Create 325 case mask&Remove != 0 && imask&uint32(InDelete|InDeleteSelf)&e.sys.Mask != 0: 326 e.event = Remove 327 case mask&Write != 0 && imask&uint32(InModify)&e.sys.Mask != 0: 328 e.event = Write 329 case mask&Rename != 0 && imask&uint32(InMovedFrom|InMoveSelf)&e.sys.Mask != 0: 330 e.event = Rename 331 default: 332 e.event = 0 333 } 334 return 335 } 336 337 // Unwatch implements notify.watcher interface. It looks for watch descriptor 338 // related to registered path and if found, calls inotify_rm_watch(2) function. 339 // This method is allowed to return EINVAL error when concurrently requested to 340 // delete identical path. 341 func (i *inotify) Unwatch(path string) (err error) { 342 iwd := int32(invalidDescriptor) 343 i.RLock() 344 for iwdkey, wd := range i.m { 345 if wd.path == path { 346 iwd = iwdkey 347 break 348 } 349 } 350 i.RUnlock() 351 if iwd == invalidDescriptor { 352 return errors.New("notify: path " + path + " is already watched") 353 } 354 fd := atomic.LoadInt32(&i.fd) 355 if err = removeInotifyWatch(fd, iwd); err != nil { 356 return 357 } 358 i.Lock() 359 delete(i.m, iwd) 360 i.Unlock() 361 return nil 362 } 363 364 // Close implements notify.watcher interface. It removes all existing watch 365 // descriptors and wakes up producer goroutine by sending data to the write end 366 // of the pipe. The function waits for a signal from producer which means that 367 // all operations on current monitoring instance are done. 368 func (i *inotify) Close() (err error) { 369 i.Lock() 370 if fd := atomic.LoadInt32(&i.fd); fd == invalidDescriptor { 371 i.Unlock() 372 return nil 373 } 374 for iwd := range i.m { 375 if e := removeInotifyWatch(i.fd, iwd); e != nil && err == nil { 376 err = e 377 } 378 delete(i.m, iwd) 379 } 380 switch _, errwrite := unix.Write(i.pipefd[1], []byte{0x00}); { 381 case errwrite != nil && err == nil: 382 err = errwrite 383 fallthrough 384 case errwrite != nil: 385 i.Unlock() 386 default: 387 i.Unlock() 388 i.wg.Wait() 389 } 390 return 391 } 392 393 // if path was removed, notify already removed the watch and returns EINVAL error 394 func removeInotifyWatch(fd int32, iwd int32) (err error) { 395 if _, err = unix.InotifyRmWatch(int(fd), uint32(iwd)); err != nil && err != unix.EINVAL { 396 return 397 } 398 return nil 399 }