Store copy actions and errors in DB.

README.md

@@ -41,9 +41,9 @@ expanded it by adding four more mirrors. ZFS doesn't automatically rebalance
 existing data, but does skew writes of new data so that more go to the newer
 mirrors.
 
-To rebalance the data manually, the algorithm is straightforward:
+To rebalance the data, the algorithm is straightforward:
 
-    for file in dataset,
+* for file in dataset,
   * copy the file to a temporary directory in another dataset
   * delete the original file
   * copy from the temporary directory to recreate the original file

datashake.go

@@ -49,7 +49,7 @@ func main() {
 	running.Store(true)
 	go func() {
 		if err := filepath.WalkDir(*sourceDir, process); err != nil {
-			errors <- err
+			fmt.Println("error:", err)
 		}
 		pending.Wait()
 		close(errors)
@@ -60,7 +60,7 @@ Loop:
 		select {
 		case err, ok := <-errors:
 			if ok {
-				fmt.Println("error:", err)
+				db.Alert(err)
 			} else {
 				break Loop
 			}
@@ -80,7 +80,7 @@ var (
 
 	tasks   *pool.Pool
 	pending sync.WaitGroup
-	errors  = make(chan error)
+	errors  = make(chan Error)
 
 	db = DB{
 		Processed: make(map[string]struct{}),
@@ -113,14 +113,26 @@ func process(path string, d fs.DirEntry, err error) (typicallyNil error) {
 // work rebalances a single file.
 func work(path string, d fs.DirEntry) {
 	var err error
+	var srcFilePath = path
+	var tempFilePath string
+
+	reportErr := func(reported error) {
+		e := Error{
+			Message:  reported.Error(),
+			FilePath: srcFilePath,
+			TempPath: tempFilePath,
+		}
+		errors <- e
+	}
+
 	defer func() {
 		if err != nil {
-			errors <- err
+			reportErr(err)
 		}
 	}()
 
 	srcFileName := d.Name()
-	srcFilePath, err := filepath.Abs(path)
+	srcFilePath, err = filepath.Abs(path)
 	if err != nil {
 		return
 	}
@@ -139,7 +151,7 @@ func work(path string, d fs.DirEntry) {
 	if err != nil {
 		return
 	}
-	tempFilePath := filepath.Join(tempDirPath, srcFileName)
+	tempFilePath = filepath.Join(tempDirPath, srcFileName)
 	safeToRemoveTemp := true
 	defer func() {
 		if !safeToRemoveTemp {
@@ -147,11 +159,11 @@ func work(path string, d fs.DirEntry) {
 				"%s may be lost in %s",
 				srcFilePath, tempDirPath,
 			)
-			errors <- err
+			reportErr(err)
 			return
 		}
 		if err := os.RemoveAll(tempDirPath); err != nil {
-			errors <- err
+			reportErr(err)
 		}
 	}()
 
@@ -213,7 +225,14 @@ func copy(srcPath, dstPath string) error {
 	}
 
 	_, err = io.Copy(dstFile, srcFile)
+	if err != nil {
 		return err
+	}
+	db.Record(Action{
+		Source:      srcPath,
+		Destination: dstPath,
+	})
+	return nil
 }
 
 // DB holds a set of files which have been rebalanced.
@@ -224,6 +243,19 @@ func copy(srcPath, dstPath string) error {
 // back to that JSON file as the program finishes.
 type DB struct {
 	Processed map[string]struct{}
+	Log       []Action
+	Errors    []Error
+}
+
+type Action struct {
+	Source      string
+	Destination string
+}
+
+type Error struct {
+	Message  string
+	FilePath string
+	TempPath string
 }
 
 func (db *DB) Contains(path string) bool {
@@ -239,6 +271,18 @@ func (db *DB) Remember(path string) {
 	db.Processed[path] = struct{}{}
 }
 
+func (db *DB) Record(a Action) {
+	dbLock.Lock()
+	defer dbLock.Unlock()
+	db.Log = append(db.Log, a)
+}
+
+func (db *DB) Alert(e Error) {
+	dbLock.Lock()
+	defer dbLock.Unlock()
+	db.Errors = append(db.Errors, e)
+}
+
 func loadDb() error {
 	if *dbPath == "" {
 		return nil