Store copy actions and errors in DB.

README.md

@@ -41,13 +41,13 @@ 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,
-      * copy the file to a temporary directory in another dataset
-      * delete the original file
-      * copy from the temporary directory to recreate the original file
-      * delete the temporary directory
+* 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
+  * delete the temporary directory
 
 As the files get rewritten, not only do the newer mirrors get more full, but
 also the older mirrors free up space. Eventually, the utilization of all mirrors

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)
-	return err
+	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