From 3da4bd9aede0f9d4c7fd1fe262b1f85a726a5a18 Mon Sep 17 00:00:00 2001
From: "Alexander \"Arav\" Andreev" <me@arav.top>
Date: Thu, 31 Mar 2022 15:33:55 +0400
Subject: [PATCH] Copied Inotify watcher with addition of ModMask.

---
 pkg/watcher/linux.go | 85 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 pkg/watcher/linux.go

diff --git a/pkg/watcher/linux.go b/pkg/watcher/linux.go
new file mode 100644
index 0000000..864a7cf
--- /dev/null
+++ b/pkg/watcher/linux.go
@@ -0,0 +1,85 @@
+package watcher
+
+import (
+	"syscall"
+	"unsafe"
+
+	"github.com/pkg/errors"
+)
+
+const (
+	CrDelMask uint32 = syscall.IN_CREATE | syscall.IN_DELETE
+	ModMask   uint32 = syscall.IN_MODIFY
+)
+
+const inotifyCount = 16
+
+type InotifyWatcher struct {
+	fd     int
+	wds    []int
+	closed bool
+}
+
+func NewInotifyWatcher() (w *InotifyWatcher, err error) {
+	w = &InotifyWatcher{closed: false}
+
+	w.fd, err = syscall.InotifyInit()
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to initialise inotify watcher")
+	}
+
+	w.wds = make([]int, 0)
+
+	return w, nil
+}
+
+func (w *InotifyWatcher) AddWatch(path string, mask uint32) error {
+	wd, err := syscall.InotifyAddWatch(w.fd, path, mask)
+	if err != nil {
+		return errors.Wrapf(err, "failed to set %s on watch", path)
+	}
+
+	w.wds = append(w.wds, wd)
+
+	return nil
+}
+
+// WatchForMask checking for events from mask and returns inotify mask to channel.
+func (w *InotifyWatcher) WatchForMask(fired chan uint32, mask uint32) {
+	go func() {
+		for !w.closed {
+			buffer := make([]byte, syscall.SizeofInotifyEvent*inotifyCount)
+			n, err := syscall.Read(w.fd, buffer)
+			if err != nil {
+				break
+			}
+
+			if n < syscall.SizeofInotifyEvent {
+				continue
+			}
+
+			for offset := 0; offset < len(buffer); offset += syscall.SizeofInotifyEvent {
+				event := (*syscall.InotifyEvent)(unsafe.Pointer(&buffer[offset]))
+				if event.Mask&mask > 0 {
+					fired <- event.Mask
+				}
+			}
+		}
+	}()
+}
+
+func (w *InotifyWatcher) Close() error {
+	for _, wd := range w.wds {
+		if _, err := syscall.InotifyRmWatch(w.fd, uint32(wd)); err != nil {
+			return err
+		}
+	}
+
+	if err := syscall.Close(w.fd); err != nil {
+		return err
+	}
+
+	w.closed = true
+
+	return nil
+}