podman/pkg/hooks/monitor.go

package hooks

import (
	"context"

	current "github.com/containers/podman/v2/pkg/hooks/1.0.0"
	"github.com/fsnotify/fsnotify"
	"github.com/sirupsen/logrus"
)

// Monitor dynamically monitors hook directories for additions,
// updates, and removals.
//
// This function writes two empty structs to the sync channel: the
// first is written after the watchers are established and the second
// when this function exits.  The expected usage is:
//
//   ctx, cancel := context.WithCancel(context.Background())
//   sync := make(chan error, 2)
//   go m.Monitor(ctx, sync)
//   err := <-sync // block until writers are established
//   if err != nil {
//     return err // failed to establish watchers
//   }
//   // do stuff
//   cancel()
//   err = <-sync // block until monitor finishes
func (m *Manager) Monitor(ctx context.Context, sync chan<- error) {
	watcher, err := fsnotify.NewWatcher()
	if err != nil {
		sync <- err
		return
	}
	defer watcher.Close()

	for _, dir := range m.directories {
		err = watcher.Add(dir)
		if err != nil {
			logrus.Errorf("failed to watch %q for hooks", dir)
			sync <- err
			return
		}
		logrus.Debugf("monitoring %q for hooks", dir)
	}

	sync <- nil

	for {
		select {
		case event := <-watcher.Events:
			m.hooks = make(map[string]*current.Hook)
			for _, dir := range m.directories {
				err = ReadDir(dir, m.extensionStages, m.hooks)
				if err != nil {
					logrus.Errorf("failed loading hooks for %s: %v", event.Name, err)
				}
			}
		case <-ctx.Done():
			err = ctx.Err()
			logrus.Debugf("hook monitoring canceled: %v", err)
			sync <- err
			close(sync)
			return
		}
	}
}