add some hacky experiments for inotify event parsing

internal/inotify/inotify.go

@@ -2,13 +2,16 @@ package inotify
 
 import (
 	"fmt"
+	"log"
+	"strings"
+	"unsafe"
 
 	"golang.org/x/sys/unix"
 )
 
 type Inotify struct {
 	fd       int
-	watchers []*watcher
+	watchers map[int]*watcher
 	ping     chan struct{}
 	paused   bool
 }
@@ -20,9 +23,10 @@ func NewInotify(ping chan struct{}) (*Inotify, error) {
 	}
 
 	i := &Inotify{
-		fd:     fd,
-		ping:   ping,
-		paused: false,
+		fd:       fd,
+		watchers: make(map[int]*watcher),
+		ping:     ping,
+		paused:   false,
 	}
 	go watch(i)
 
@@ -34,7 +38,14 @@ func (i *Inotify) Watch(dir string) error {
 	if err != nil {
 		return fmt.Errorf("creating watcher: %v", err)
 	}
-	i.watchers = append(i.watchers, w)
+	i.watchers[w.wd] = w
+	return nil
+}
+
+func (i *Inotify) Close() error {
+	if err := unix.Close(i.fd); err != nil {
+		return fmt.Errorf("closing inotify file descriptor: %v", err)
+	}
 	return nil
 }
 
@@ -47,19 +58,104 @@ func (i *Inotify) UnPause() {
 }
 
 func (i *Inotify) String() string {
-	dirs := make([]string, 0)
-	for _, w := range i.watchers {
-		dirs = append(dirs, w.dir)
+	if len(i.watchers) < 20 {
+		dirs := make([]string, 0)
+		for _, w := range i.watchers {
+			dirs = append(dirs, w.dir)
+		}
+		return fmt.Sprintf("Watching: %v", dirs)
+	} else {
+		return fmt.Sprintf("Watching %d directories", len(i.watchers))
 	}
-	return fmt.Sprintf("Watching: %v", dirs)
+}
+
+type bufRead struct {
+	n   int
+	buf []byte
 }
 
 func watch(i *Inotify) {
-	buf := make([]byte, 1024)
+	buf := make([]byte, 20*unix.SizeofInotifyEvent)
+	buffers := make(chan bufRead)
+	go verboseWatcher(i, buffers)
 	for {
-		_, _ = unix.Read(i.fd, buf)
+		n, _ := unix.Read(i.fd, buf)
 		if !i.paused {
 			i.ping <- struct{}{}
 		}
+		buffers <- bufRead{
+			n:   n,
+			buf: buf,
+		}
 	}
 }
+
+func verboseWatcher(i *Inotify, buffers chan bufRead) {
+	for bf := range buffers {
+		n := bf.n
+		buf := bf.buf
+
+		if n < unix.SizeofInotifyEvent {
+			if n == 0 {
+				// If EOF is received. This should really never happen.
+				panic(fmt.Sprintf("No bytes read from fd"))
+			} else if n < 0 {
+				// If an error occurred while reading.
+				log.Printf("ERROR: reading from inotify: %d", n)
+			} else {
+				// Read was too short.
+				log.Printf("ERROR: Short read")
+			}
+			continue
+		}
+
+		var offset uint32
+		for offset <= uint32(n-unix.SizeofInotifyEvent) {
+			raw := (*unix.InotifyEvent)(unsafe.Pointer(&buf[offset]))
+
+			mask := uint32(raw.Mask)
+			nameLen := uint32(raw.Len)
+
+			name := i.watchers[int(raw.Wd)].dir
+			if nameLen > 0 {
+				bytes := (*[unix.PathMax]byte)(unsafe.Pointer(&buf[offset+unix.SizeofInotifyEvent]))
+				if uint32(len(bytes)) > nameLen {
+					name += "/" + strings.TrimRight(string(bytes[0:nameLen]), "\000")
+				}
+			}
+			ev := newEvent(name, mask)
+			log.Printf("### %+v", ev)
+
+			offset += unix.SizeofInotifyEvent + nameLen
+		}
+	}
+}
+
+type Event struct {
+	name string
+	op   string
+}
+
+func (e Event) String() string {
+	return fmt.Sprintf("%10s | %s", e.op, e.name)
+}
+
+func 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
+}

internal/inotify/watcher.go

@@ -2,11 +2,15 @@ package inotify
 
 import (
 	"fmt"
+	"io/ioutil"
+	"strconv"
+	"strings"
 
 	"golang.org/x/sys/unix"
 )
 
 const events = unix.IN_ALL_EVENTS
+const MaximumWatchersFile = "/proc/sys/fs/inotify/max_user_watches"
 
 type watcher struct {
 	wd  int
@@ -23,3 +27,18 @@ func newWatcher(fd int, dir string, ping chan struct{}) (*watcher, error) {
 		dir: dir,
 	}, nil
 }
+
+func WatcherLimit() (int, error) {
+	b, err := ioutil.ReadFile(MaximumWatchersFile)
+	if err != nil {
+		return 0, fmt.Errorf("reading from %s: %v", MaximumWatchersFile, err)
+	}
+
+	s := strings.TrimSpace(string(b))
+	m, err := strconv.Atoi(s)
+	if err != nil {
+		return 0, fmt.Errorf("converting to integer: %v", err)
+	}
+
+	return m, nil
+}