auth/vendor/github.com/fsnotify/fsnotify/backend_inotify.go

460 lines
14 KiB
Go

//go:build linux
// +build linux
package fsnotify
import (
"errors"
"fmt"
"io"
"os"
"path/filepath"
"strings"
"sync"
"unsafe"
"golang.org/x/sys/unix"
)
// Watcher watches a set of paths, delivering events on a channel.
//
// A watcher should not be copied (e.g. pass it by pointer, rather than by
// value).
//
// # Linux notes
//
// When a file is removed a Remove event won't be emitted until all file
// descriptors are closed, and deletes will always emit a Chmod. For example:
//
// fp := os.Open("file")
// os.Remove("file") // Triggers Chmod
// fp.Close() // Triggers Remove
//
// This is the event that inotify sends, so not much can be changed about this.
//
// The fs.inotify.max_user_watches sysctl variable specifies the upper limit
// for the number of watches per user, and fs.inotify.max_user_instances
// specifies the maximum number of inotify instances per user. Every Watcher you
// create is an "instance", and every path you add is a "watch".
//
// These are also exposed in /proc as /proc/sys/fs/inotify/max_user_watches and
// /proc/sys/fs/inotify/max_user_instances
//
// To increase them you can use sysctl or write the value to the /proc file:
//
// # Default values on Linux 5.18
// sysctl fs.inotify.max_user_watches=124983
// sysctl fs.inotify.max_user_instances=128
//
// To make the changes persist on reboot edit /etc/sysctl.conf or
// /usr/lib/sysctl.d/50-default.conf (details differ per Linux distro; check
// your distro's documentation):
//
// fs.inotify.max_user_watches=124983
// fs.inotify.max_user_instances=128
//
// Reaching the limit will result in a "no space left on device" or "too many open
// files" error.
//
// # kqueue notes (macOS, BSD)
//
// kqueue requires opening a file descriptor for every file that's being watched;
// so if you're watching a directory with five files then that's six file
// descriptors. You will run in to your system's "max open files" limit faster on
// these platforms.
//
// The sysctl variables kern.maxfiles and kern.maxfilesperproc can be used to
// control the maximum number of open files, as well as /etc/login.conf on BSD
// systems.
//
// # macOS notes
//
// Spotlight indexing on macOS can result in multiple events (see [#15]). A
// temporary workaround is to add your folder(s) to the "Spotlight Privacy
// Settings" until we have a native FSEvents implementation (see [#11]).
//
// [#11]: https://github.com/fsnotify/fsnotify/issues/11
// [#15]: https://github.com/fsnotify/fsnotify/issues/15
type Watcher struct {
// Events sends the filesystem change events.
//
// fsnotify can send the following events; a "path" here can refer to a
// file, directory, symbolic link, or special file like a FIFO.
//
// fsnotify.Create A new path was created; this may be followed by one
// or more Write events if data also gets written to a
// file.
//
// fsnotify.Remove A path was removed.
//
// fsnotify.Rename A path was renamed. A rename is always sent with the
// old path as Event.Name, and a Create event will be
// sent with the new name. Renames are only sent for
// paths that are currently watched; e.g. moving an
// unmonitored file into a monitored directory will
// show up as just a Create. Similarly, renaming a file
// to outside a monitored directory will show up as
// only a Rename.
//
// fsnotify.Write A file or named pipe was written to. A Truncate will
// also trigger a Write. A single "write action"
// initiated by the user may show up as one or multiple
// writes, depending on when the system syncs things to
// disk. For example when compiling a large Go program
// you may get hundreds of Write events, so you
// probably want to wait until you've stopped receiving
// them (see the dedup example in cmd/fsnotify).
//
// fsnotify.Chmod Attributes were changed. On Linux this is also sent
// when a file is removed (or more accurately, when a
// link to an inode is removed). On kqueue it's sent
// and on kqueue when a file is truncated. On Windows
// it's never sent.
Events chan Event
// Errors sends any errors.
Errors chan error
// Store fd here as os.File.Read() will no longer return on close after
// calling Fd(). See: https://github.com/golang/go/issues/26439
fd int
mu sync.Mutex // Map access
inotifyFile *os.File
watches map[string]*watch // Map of inotify watches (key: path)
paths map[int]string // Map of watched paths (key: watch descriptor)
done chan struct{} // Channel for sending a "quit message" to the reader goroutine
doneResp chan struct{} // Channel to respond to Close
}
// NewWatcher creates a new Watcher.
func NewWatcher() (*Watcher, error) {
// Create inotify fd
// Need to set the FD to nonblocking mode in order for SetDeadline methods to work
// Otherwise, blocking i/o operations won't terminate on close
fd, errno := unix.InotifyInit1(unix.IN_CLOEXEC | unix.IN_NONBLOCK)
if fd == -1 {
return nil, errno
}
w := &Watcher{
fd: fd,
inotifyFile: os.NewFile(uintptr(fd), ""),
watches: make(map[string]*watch),
paths: make(map[int]string),
Events: make(chan Event),
Errors: make(chan error),
done: make(chan struct{}),
doneResp: make(chan struct{}),
}
go w.readEvents()
return w, nil
}
// Returns true if the event was sent, or false if watcher is closed.
func (w *Watcher) sendEvent(e Event) bool {
select {
case w.Events <- e:
return true
case <-w.done:
}
return false
}
// Returns true if the error was sent, or false if watcher is closed.
func (w *Watcher) sendError(err error) bool {
select {
case w.Errors <- err:
return true
case <-w.done:
return false
}
}
func (w *Watcher) isClosed() bool {
select {
case <-w.done:
return true
default:
return false
}
}
// Close removes all watches and closes the events channel.
func (w *Watcher) Close() error {
w.mu.Lock()
if w.isClosed() {
w.mu.Unlock()
return nil
}
// Send 'close' signal to goroutine, and set the Watcher to closed.
close(w.done)
w.mu.Unlock()
// Causes any blocking reads to return with an error, provided the file
// still supports deadline operations.
err := w.inotifyFile.Close()
if err != nil {
return err
}
// Wait for goroutine to close
<-w.doneResp
return nil
}
// Add starts monitoring the path for changes.
//
// A path can only be watched once; attempting to watch it more than once will
// return an error. Paths that do not yet exist on the filesystem cannot be
// added. A watch will be automatically removed if the path is deleted.
//
// A path will remain watched if it gets renamed to somewhere else on the same
// filesystem, but the monitor will get removed if the path gets deleted and
// re-created, or if it's moved to a different filesystem.
//
// Notifications on network filesystems (NFS, SMB, FUSE, etc.) or special
// filesystems (/proc, /sys, etc.) generally don't work.
//
// # Watching directories
//
// All files in a directory are monitored, including new files that are created
// after the watcher is started. Subdirectories are not watched (i.e. it's
// non-recursive).
//
// # Watching files
//
// Watching individual files (rather than directories) is generally not
// recommended as many tools update files atomically. Instead of "just" writing
// to the file a temporary file will be written to first, and if successful the
// temporary file is moved to to destination removing the original, or some
// variant thereof. The watcher on the original file is now lost, as it no
// longer exists.
//
// Instead, watch the parent directory and use Event.Name to filter out files
// you're not interested in. There is an example of this in [cmd/fsnotify/file.go].
func (w *Watcher) Add(name string) error {
name = filepath.Clean(name)
if w.isClosed() {
return errors.New("inotify instance already closed")
}
var flags uint32 = unix.IN_MOVED_TO | unix.IN_MOVED_FROM |
unix.IN_CREATE | unix.IN_ATTRIB | unix.IN_MODIFY |
unix.IN_MOVE_SELF | unix.IN_DELETE | unix.IN_DELETE_SELF
w.mu.Lock()
defer w.mu.Unlock()
watchEntry := w.watches[name]
if watchEntry != nil {
flags |= watchEntry.flags | unix.IN_MASK_ADD
}
wd, errno := unix.InotifyAddWatch(w.fd, name, flags)
if wd == -1 {
return errno
}
if watchEntry == nil {
w.watches[name] = &watch{wd: uint32(wd), flags: flags}
w.paths[wd] = name
} else {
watchEntry.wd = uint32(wd)
watchEntry.flags = flags
}
return nil
}
// Remove stops monitoring the path for changes.
//
// Directories are always removed non-recursively. For example, if you added
// /tmp/dir and /tmp/dir/subdir then you will need to remove both.
//
// Removing a path that has not yet been added returns [ErrNonExistentWatch].
func (w *Watcher) Remove(name string) error {
name = filepath.Clean(name)
// Fetch the watch.
w.mu.Lock()
defer w.mu.Unlock()
watch, ok := w.watches[name]
// Remove it from inotify.
if !ok {
return fmt.Errorf("%w: %s", ErrNonExistentWatch, name)
}
// We successfully removed the watch if InotifyRmWatch doesn't return an
// error, we need to clean up our internal state to ensure it matches
// inotify's kernel state.
delete(w.paths, int(watch.wd))
delete(w.watches, name)
// inotify_rm_watch will return EINVAL if the file has been deleted;
// the inotify will already have been removed.
// watches and pathes are deleted in ignoreLinux() implicitly and asynchronously
// by calling inotify_rm_watch() below. e.g. readEvents() goroutine receives IN_IGNORE
// so that EINVAL means that the wd is being rm_watch()ed or its file removed
// by another thread and we have not received IN_IGNORE event.
success, errno := unix.InotifyRmWatch(w.fd, watch.wd)
if success == -1 {
// TODO: Perhaps it's not helpful to return an error here in every case;
// The only two possible errors are:
//
// - EBADF, which happens when w.fd is not a valid file descriptor
// of any kind.
// - EINVAL, which is when fd is not an inotify descriptor or wd
// is not a valid watch descriptor. Watch descriptors are
// invalidated when they are removed explicitly or implicitly;
// explicitly by inotify_rm_watch, implicitly when the file they
// are watching is deleted.
return errno
}
return nil
}
// WatchList returns all paths added with [Add] (and are not yet removed).
func (w *Watcher) WatchList() []string {
w.mu.Lock()
defer w.mu.Unlock()
entries := make([]string, 0, len(w.watches))
for pathname := range w.watches {
entries = append(entries, pathname)
}
return entries
}
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)
}
// readEvents reads from the inotify file descriptor, converts the
// received events into Event objects and sends them via the Events channel
func (w *Watcher) readEvents() {
defer func() {
close(w.doneResp)
close(w.Errors)
close(w.Events)
}()
var (
buf [unix.SizeofInotifyEvent * 4096]byte // Buffer for a maximum of 4096 raw events
errno error // Syscall errno
)
for {
// See if we have been closed.
if w.isClosed() {
return
}
n, err := w.inotifyFile.Read(buf[:])
switch {
case errors.Unwrap(err) == os.ErrClosed:
return
case err != nil:
if !w.sendError(err) {
return
}
continue
}
if n < unix.SizeofInotifyEvent {
var err error
if n == 0 {
// If EOF is received. This should really never happen.
err = io.EOF
} else if n < 0 {
// If an error occurred while reading.
err = errno
} else {
// Read was too short.
err = errors.New("notify: short read in readEvents()")
}
if !w.sendError(err) {
return
}
continue
}
var offset uint32
// 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-unix.SizeofInotifyEvent) {
var (
// Point "raw" to the event in the buffer
raw = (*unix.InotifyEvent)(unsafe.Pointer(&buf[offset]))
mask = uint32(raw.Mask)
nameLen = uint32(raw.Len)
)
if mask&unix.IN_Q_OVERFLOW != 0 {
if !w.sendError(ErrEventOverflow) {
return
}
}
// 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()
name, ok := w.paths[int(raw.Wd)]
// IN_DELETE_SELF occurs when the file/directory being watched is removed.
// This is a sign to clean up the maps, otherwise we are no longer in sync
// with the inotify kernel state which has already deleted the watch
// automatically.
if ok && mask&unix.IN_DELETE_SELF == unix.IN_DELETE_SELF {
delete(w.paths, int(raw.Wd))
delete(w.watches, name)
}
w.mu.Unlock()
if nameLen > 0 {
// Point "bytes" at the first byte of the filename
bytes := (*[unix.PathMax]byte)(unsafe.Pointer(&buf[offset+unix.SizeofInotifyEvent]))[:nameLen:nameLen]
// The filename is padded with NULL bytes. TrimRight() gets rid of those.
name += "/" + strings.TrimRight(string(bytes[0:nameLen]), "\000")
}
event := w.newEvent(name, mask)
// Send the events that are not ignored on the events channel
if mask&unix.IN_IGNORED == 0 {
if !w.sendEvent(event) {
return
}
}
// Move to the next event in the buffer
offset += unix.SizeofInotifyEvent + nameLen
}
}
}
// newEvent returns an platform-independent Event based on an inotify mask.
func (w *Watcher) newEvent(name string, mask uint32) Event {
e := Event{Name: name}
if mask&unix.IN_CREATE == unix.IN_CREATE || mask&unix.IN_MOVED_TO == unix.IN_MOVED_TO {
e.Op |= Create
}
if mask&unix.IN_DELETE_SELF == unix.IN_DELETE_SELF || mask&unix.IN_DELETE == unix.IN_DELETE {
e.Op |= Remove
}
if mask&unix.IN_MODIFY == unix.IN_MODIFY {
e.Op |= Write
}
if mask&unix.IN_MOVE_SELF == unix.IN_MOVE_SELF || mask&unix.IN_MOVED_FROM == unix.IN_MOVED_FROM {
e.Op |= Rename
}
if mask&unix.IN_ATTRIB == unix.IN_ATTRIB {
e.Op |= Chmod
}
return e
}