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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
//go:build linux && !android
// Package linuxdnsfight provides Linux support for detecting DNS fights
// (inotify watching of /etc/resolv.conf).
package linuxdnsfight
import (
"context"
"fmt"
"github.com/illarion/gonotify/v3"
"tailscale.com/net/dns"
)
func init() {
dns.HookWatchFile.Set(watchFile)
}
// watchFile sets up an inotify watch for a given directory and
// calls the callback function every time a particular file is changed.
// The filename should be located in the provided directory.
func watchFile(ctx context.Context, dir, filename string, cb func()) error {
ctx, cancel := context.WithCancel(ctx)
defer cancel()
const events = gonotify.IN_ATTRIB |
gonotify.IN_CLOSE_WRITE |
gonotify.IN_CREATE |
gonotify.IN_DELETE |
gonotify.IN_MODIFY |
gonotify.IN_MOVE
watcher, err := gonotify.NewDirWatcher(ctx, events, dir)
if err != nil {
return fmt.Errorf("NewDirWatcher: %w", err)
}
for {
select {
case event := <-watcher.C:
if event.Name == filename {
cb()
}
case <-ctx.Done():
return ctx.Err()
}
}
}
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