lib/fs, lib/model: Add warning about kqueue resource usage (fixes #7855) (#8249)

lib/fs/basicfs_watch_eventtypes_kqueue.go

@@ -18,4 +18,7 @@ const (
 	subEventMask  = notify.NoteDelete | notify.NoteWrite | notify.NoteRename | notify.Create | notify.NoteAttrib | notify.NoteExtend
 	permEventMask = 0
 	rmEventMask   = notify.NoteDelete | notify.NoteRename
+
+	// WatchKqueue indicates if kqueue is used for filesystem watching
+	WatchKqueue = true
 )

lib/fs/basicfs_watch_notkqueue.go

@@ -0,0 +1,13 @@
+// Copyright (C) 2022 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/.
+
+//go:build !dragonfly && !freebsd && !netbsd && !openbsd
+// +build !dragonfly,!freebsd,!netbsd,!openbsd
+
+package fs
+
+// WatchKqueue indicates if kqueue is used for filesystem watching
+const WatchKqueue = false