added fs encryption overlay

pkg/provider/os/os.go

@@ -0,0 +1,61 @@
+// Copyright (C) 2022 Marius Schellenberger
+
+package os
+
+import (
+	"cachefs/pkg/provider"
+	"io/fs"
+	"os"
+	"path"
+	"path/filepath"
+
+	"golang.org/x/sys/unix"
+)
+
+var _ provider.FS = (*FS)(nil)
+
+type FS struct {
+	root string
+}
+
+func NewFS(root string) (*FS, error) {
+	return &FS{root}, nil
+}
+
+func (fs *FS) path(p string) string {
+	return filepath.Join(fs.root, filepath.FromSlash(path.Clean("/"+p)))
+}
+
+func (fs *FS) Stat(p string) (fs.FileInfo, error) {
+	return os.Stat(fs.path(p))
+}
+
+func (fs *FS) Remove(p string) error {
+	return os.Remove(fs.path(p))
+}
+
+func (fs *FS) Open(p string) (provider.File, error) {
+	return os.Open(fs.path(p))
+}
+
+func (fs *FS) OpenFile(p string, flags int, mode os.FileMode) (provider.File, error) {
+	return os.OpenFile(fs.path(p), flags, mode)
+}
+
+func (fs *FS) MkdirAll(p string, mode os.FileMode) error {
+	return os.MkdirAll(fs.path(p), mode)
+}
+
+func (fs *FS) Root() string {
+	return fs.root
+}
+
+func (fs *FS) Fstat(fd uintptr) (int64, error) {
+	var stat unix.Stat_t
+	err := unix.Fstat(int(fd), &stat)
+	return stat.Blocks, err
+}
+
+func (FS) Close() error {
+	return nil
+}