put mfsr package back

repo/fsrepo/migrations/mfsr.go

+package mfsr
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path"
+	"strings"
+)
+
+const VersionFile = "version"
+
+type RepoPath string
+
+func (rp RepoPath) VersionFile() string {
+	return path.Join(string(rp), VersionFile)
+}
+
+func (rp RepoPath) Version() (string, error) {
+	if rp == "" {
+		return "", fmt.Errorf("invalid repo path \"%s\"", rp)
+	}
+
+	fn := rp.VersionFile()
+	if _, err := os.Stat(fn); os.IsNotExist(err) {
+		return "", VersionFileNotFound(rp)
+	}
+
+	c, err := ioutil.ReadFile(fn)
+	if err != nil {
+		return "", err
+	}
+
+	s := string(c)
+	s = strings.TrimSpace(s)
+	return s, nil
+}
+
+func (rp RepoPath) CheckVersion(version string) error {
+	v, err := rp.Version()
+	if err != nil {
+		return err
+	}
+
+	if v != version {
+		return fmt.Errorf("versions differ (expected: %s, actual:%s)", version, v)
+	}
+
+	return nil
+}
+
+func (rp RepoPath) WriteVersion(version string) error {
+	fn := rp.VersionFile()
+	return ioutil.WriteFile(fn, []byte(version+"\n"), 0644)
+}
+
+type VersionFileNotFound string
+
+func (v VersionFileNotFound) Error() string {
+	return "no version file in repo at " + string(v)
+}