syncthing/lib/fs/basicfs_watch.go

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// Copyright (C) 2016 The Syncthing Authors.
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this file,
// You can obtain one at http://mozilla.org/MPL/2.0/.
// +build !solaris,!darwin solaris,cgo darwin,cgo
package fs
import (
"context"
"errors"
"path/filepath"
"github.com/zillode/notify"
)
// Notify does not block on sending to channel, so the channel must be buffered.
// The actual number is magic.
// Not meant to be changed, but must be changeable for tests
var backendBuffer = 500
func (f *BasicFilesystem) Watch(name string, ignore Matcher, ctx context.Context, ignorePerms bool) (<-chan Event, error) {
absName, err := f.rooted(name)
if err != nil {
return nil, err
}
absShouldIgnore := func(absPath string) bool {
return ignore.ShouldIgnore(f.unrootedChecked(absPath))
}
outChan := make(chan Event)
backendChan := make(chan notify.EventInfo, backendBuffer)
eventMask := subEventMask
if !ignorePerms {
eventMask |= permEventMask
}
if err := notify.WatchWithFilter(filepath.Join(absName, "..."), backendChan, absShouldIgnore, eventMask); err != nil {
notify.Stop(backendChan)
if reachedMaxUserWatches(err) {
err = errors.New("failed to install inotify handler. Please increase inotify limits, see https://github.com/syncthing/syncthing-inotify#troubleshooting-for-folders-with-many-files-on-linux for more information")
}
return nil, err
}
go f.watchLoop(name, absName, backendChan, outChan, ignore, ctx)
return outChan, nil
}
func (f *BasicFilesystem) watchLoop(name string, absName string, backendChan chan notify.EventInfo, outChan chan<- Event, ignore Matcher, ctx context.Context) {
for {
// Detect channel overflow
if len(backendChan) == backendBuffer {
outer:
for {
select {
case <-backendChan:
default:
break outer
}
}
// When next scheduling a scan, do it on the entire folder as events have been lost.
outChan <- Event{Name: name, Type: NonRemove}
l.Debugln(f.Type(), f.URI(), "Watch: Event overflow, send \".\"")
}
select {
case ev := <-backendChan:
relPath := f.unrootedChecked(ev.Path())
if ignore.ShouldIgnore(relPath) {
l.Debugln(f.Type(), f.URI(), "Watch: Ignoring", relPath)
continue
}
evType := f.eventType(ev.Event())
select {
case outChan <- Event{Name: relPath, Type: evType}:
l.Debugln(f.Type(), f.URI(), "Watch: Sending", relPath, evType)
case <-ctx.Done():
notify.Stop(backendChan)
l.Debugln(f.Type(), f.URI(), "Watch: Stopped")
return
}
case <-ctx.Done():
notify.Stop(backendChan)
l.Debugln(f.Type(), f.URI(), "Watch: Stopped")
return
}
}
}
func (f *BasicFilesystem) eventType(notifyType notify.Event) EventType {
if notifyType&rmEventMask != 0 {
return Remove
}
return NonRemove
}
// unrootedChecked returns the path relative to the folder root (same as
// unrooted). It panics if the given path is not a subpath and handles the
// special case when the given path is the folder root without a trailing
// pathseparator.
func (f *BasicFilesystem) unrootedChecked(absPath string) string {
if absPath+string(PathSeparator) == f.root {
return "."
}
relPath := f.unrooted(absPath)
if relPath == absPath {
panic("bug: Notify backend is processing a change outside of the watched path: " + absPath)
}
return relPath
}