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// Copyright 2015 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.
//go:build linux
// +build linux
package fsnotify
import (
"errors"
"golang.org/x/sys/unix"
)
type fdPoller struct {
fd int // File descriptor (as returned by the inotify_init() syscall)
epfd int // Epoll file descriptor
pipe [2]int // Pipe for waking up
}
func emptyPoller(fd int) *fdPoller {
poller := new(fdPoller)
poller.fd = fd
poller.epfd = -1
poller.pipe[0] = -1
poller.pipe[1] = -1
return poller
}
// Create a new inotify poller.
// This creates an inotify handler, and an epoll handler.
func newFdPoller(fd int) (*fdPoller, error) {
var errno error
poller := emptyPoller(fd)
defer func() {
if errno != nil {
poller.close()
}
}()
// Create epoll fd
poller.epfd, errno = unix.EpollCreate1(unix.EPOLL_CLOEXEC)
if poller.epfd == -1 {
return nil, errno
}
// Create pipe; pipe[0] is the read end, pipe[1] the write end.
errno = unix.Pipe2(poller.pipe[:], unix.O_NONBLOCK|unix.O_CLOEXEC)
if errno != nil {
return nil, errno
}
// Register inotify fd with epoll
event := unix.EpollEvent{
Fd: int32(poller.fd),
Events: unix.EPOLLIN,
}
errno = unix.EpollCtl(poller.epfd, unix.EPOLL_CTL_ADD, poller.fd, &event)
if errno != nil {
return nil, errno
}
// Register pipe fd with epoll
event = unix.EpollEvent{
Fd: int32(poller.pipe[0]),
Events: unix.EPOLLIN,
}
errno = unix.EpollCtl(poller.epfd, unix.EPOLL_CTL_ADD, poller.pipe[0], &event)
if errno != nil {
return nil, errno
}
return poller, nil
}
// Wait using epoll.
// Returns true if something is ready to be read,
// false if there is not.
func (poller *fdPoller) wait() (bool, error) {
// 3 possible events per fd, and 2 fds, makes a maximum of 6 events.
// I don't know whether epoll_wait returns the number of events returned,
// or the total number of events ready.
// I decided to catch both by making the buffer one larger than the maximum.
events := make([]unix.EpollEvent, 7)
for {
n, errno := unix.EpollWait(poller.epfd, events, -1)
if n == -1 {
if errno == unix.EINTR {
continue
}
return false, errno
}
if n == 0 {
// If there are no events, try again.
continue
}
if n > 6 {
// This should never happen. More events were returned than should be possible.
return false, errors.New("epoll_wait returned more events than I know what to do with")
}
ready := events[:n]
epollhup := false
epollerr := false
epollin := false
for _, event := range ready {
if event.Fd == int32(poller.fd) {
if event.Events&unix.EPOLLHUP != 0 {
// This should not happen, but if it does, treat it as a wakeup.
epollhup = true
}
if event.Events&unix.EPOLLERR != 0 {
// If an error is waiting on the file descriptor, we should pretend
// something is ready to read, and let unix.Read pick up the error.
epollerr = true
}
if event.Events&unix.EPOLLIN != 0 {
// There is data to read.
epollin = true
}
}
if event.Fd == int32(poller.pipe[0]) {
if event.Events&unix.EPOLLHUP != 0 {
// Write pipe descriptor was closed, by us. This means we're closing down the
// watcher, and we should wake up.
}
if event.Events&unix.EPOLLERR != 0 {
// If an error is waiting on the pipe file descriptor.
// This is an absolute mystery, and should never ever happen.
return false, errors.New("Error on the pipe descriptor.")
}
if event.Events&unix.EPOLLIN != 0 {
// This is a regular wakeup, so we have to clear the buffer.
err := poller.clearWake()
if err != nil {
return false, err
}
}
}
}
if epollhup || epollerr || epollin {
return true, nil
}
return false, nil
}
}
// Close the write end of the poller.
func (poller *fdPoller) wake() error {
buf := make([]byte, 1)
n, errno := unix.Write(poller.pipe[1], buf)
if n == -1 {
if errno == unix.EAGAIN {
// Buffer is full, poller will wake.
return nil
}
return errno
}
return nil
}
func (poller *fdPoller) clearWake() error {
// You have to be woken up a LOT in order to get to 100!
buf := make([]byte, 100)
n, errno := unix.Read(poller.pipe[0], buf)
if n == -1 {
if errno == unix.EAGAIN {
// Buffer is empty, someone else cleared our wake.
return nil
}
return errno
}
return nil
}
// Close all poller file descriptors, but not the one passed to it.
func (poller *fdPoller) close() {
if poller.pipe[1] != -1 {
unix.Close(poller.pipe[1])
}
if poller.pipe[0] != -1 {
unix.Close(poller.pipe[0])
}
if poller.epfd != -1 {
unix.Close(poller.epfd)
}
}
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