Merge branch 'develop'

README.md

@@ -1 +1,5 @@
-# overlay
+# overlay
+
+Simple command to overlay directory.
+
+Useful to test things and then discard all changes at the directory.

main.go

@@ -0,0 +1,98 @@
+package main
+
+import (
+	"flag"
+	"log"
+	"os"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+func getOrElse(env, def string) string {
+	value := os.Getenv(env)
+	if value == "" {
+		return def
+	}
+	return value
+}
+
+// Overlaper has the methods to overlap a directory and discard the changes
+type Overlaper interface {
+	Overlap() error
+	Discard() error
+}
+
+func waitForClosure(timeout time.Duration) chan struct{} {
+	waitTimeout := timeout
+	if timeout == 0 {
+		waitTimeout = time.Hour * 24
+	}
+	signalChan := make(chan os.Signal)
+	signal.Notify(signalChan, os.Interrupt, os.Kill, syscall.SIGTERM)
+
+	out := make(chan struct{})
+	go func() {
+		for {
+			select {
+			case <-time.After(waitTimeout):
+				log.Printf("Timeout reached\n")
+				if timeout > 0 {
+					out <- struct{}{}
+				}
+			case s := <-signalChan:
+				log.Printf("Received signal: %s\n", s)
+				out <- struct{}{}
+			}
+		}
+	}()
+	return out
+}
+
+func main() {
+	var timeout string
+	var path string
+	var leave bool
+
+	flag.StringVar(&timeout, "t", getOrElse("OVERLAP_DURATION", "0s"), "Time to overlay (0 = infinity)")
+	flag.BoolVar(&leave, "l", false, "Leave the directory overlapped and exit")
+	flag.Parse()
+
+	if args := flag.Args(); len(args) != 1 {
+		log.Fatalf("Only one argument must be provided")
+	} else {
+		path = args[0]
+	}
+
+	durationTimeout, err := time.ParseDuration(timeout)
+	if err != nil {
+		log.Fatalf("Duration provided isn't valid: %s\n", err)
+	}
+
+	o := OverlayFS{Directory: path}
+	if err = o.Overlap(); err != nil {
+		log.Fatalf("Error overlapping directory: %s\n", err)
+	}
+	log.Printf("Directory %s overlapped correctly\n", path)
+
+	if !leave {
+		out := waitForClosure(durationTimeout)
+		for {
+			select {
+			case <-out:
+				if err := o.Discard(); err != nil {
+					log.Printf("Error discarding directory: %s\n", err)
+					go func() {
+						retryTime := time.Second * 5
+						log.Printf("Retrying in %s\n", retryTime)
+						time.Sleep(retryTime)
+						out <- struct{}{}
+					}()
+				} else {
+					log.Printf("Changes to directory %s discarded\n", path)
+					return
+				}
+			}
+		}
+	}
+}

overlayfs.go

@@ -0,0 +1,42 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"syscall"
+)
+
+type OverlayFS struct {
+	Directory string
+	upperdir  string
+	workdir   string
+}
+
+func (o *OverlayFS) Overlap() error {
+	file, err := os.Open(o.Directory)
+	if err != nil {
+		return fmt.Errorf("Can't open directory: %s", err)
+	}
+	fileInfo, err := file.Stat()
+	if err != nil {
+		return fmt.Errorf("Can't open directory: %s", err)
+	}
+	stats := fileInfo.Sys().(*syscall.Stat_t)
+
+	o.upperdir, _ = ioutil.TempDir("", "shadowud")
+	o.workdir, _ = ioutil.TempDir("", "shadowwd")
+
+	if err := syscall.Mount("overlay", o.Directory, "overlay", uintptr(0), fmt.Sprintf("lowerdir=%s,upperdir=%s,workdir=%s", o.Directory, o.upperdir, o.workdir)); err != nil {
+		return fmt.Errorf("Can't mount directory: %s", err)
+	}
+	os.Chown(o.Directory, int(stats.Uid), int(stats.Gid))
+
+	return nil
+}
+
+func (o *OverlayFS) Discard() error {
+	defer os.RemoveAll(o.upperdir)
+	defer os.RemoveAll(o.workdir)
+	return syscall.Unmount(o.Directory, 0)
+}