Fix rotating log makes dfdaemon.log file huge size

When the size of dfdaemon.log file large than 20M,
the size of log file will continuous growth up.

Use Mmap to copy the file which need be truncated.

Related to issue:
dragonflyoss/dragonfly#364

Signed-off-by: godliness <[email protected]>

dfdaemon/initializer/initializer.go

@@ -18,7 +18,6 @@ package initializer
 
 import (
 	"fmt"
-	"io"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -102,32 +101,31 @@ func cleanLocalRepo(options *options.Options) {
 }
 
 // rotateLog truncates the logs file by a certain amount bytes.
-func rotateLog(logFile *os.File, logFilePath string) {
+func rotateLog(logFile *os.File) error {
+	stat, err := logFile.Stat()
+	if err != nil {
+		return err
+	}
 	logSizeLimit := int64(20 * 1024 * 1024)
-	for {
-		time.Sleep(time.Second * 60)
-		stat, err := os.Stat(logFilePath)
+	// if it exceeds the 20MB limitation
+	if stat.Size() > logSizeLimit {
+		log.SetOutput(ioutil.Discard)
+		// make sure set log output back to logFile when error raised.
+		defer log.SetOutput(logFile)
+		logFile.Sync()
+		truncateSize := logSizeLimit/2 - 1
+		mem, err := syscall.Mmap(int(logFile.Fd()), 0, int(stat.Size()), syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED)
 		if err != nil {
-			log.Errorf("failed to stat %s: %s", logFilePath, err)
-			continue
+			return err
 		}
-		// if it exceeds the 20MB limitation
-		if stat.Size() > logSizeLimit {
-			log.SetOutput(ioutil.Discard)
-			logFile.Sync()
-			if transFile, err := os.Open(logFilePath); err == nil {
-				// move the pointer to be (end - 10MB)
-				transFile.Seek(-10*1024*1024, 2)
-				// move the pointer to head
-				logFile.Seek(0, 0)
-				count, _ := io.Copy(logFile, transFile)
-				logFile.Truncate(count)
-				log.SetOutput(logFile)
-				transFile.Close()
-			}
+		copy(mem[0:], mem[truncateSize:])
+		if err := syscall.Munmap(mem); err != nil {
+			return err
 		}
+		logFile.Truncate(stat.Size() - truncateSize)
+		logFile.Seek(truncateSize, 0)
 	}
-
+	return nil
 }
 
 func initLogger() {
@@ -148,7 +146,15 @@ func initLogger() {
 		if logFile, err := os.OpenFile(logFilePath, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0644); err == nil {
 			logFile.Seek(0, 2)
 			log.SetOutput(logFile)
-			go rotateLog(logFile, logFilePath)
+			go func(logFile *os.File) {
+				ticker := time.NewTicker(60 * time.Second)
+				for range ticker.C {
+					if err := rotateLog(logFile); err != nil {
+						// write error log into os.Stderr directly to avoid writing to a broken log file.
+						fmt.Fprintf(os.Stderr, "failed to rotate log %s: %v\n", logFile.Name(), err)
+					}
+				}
+			}(logFile)
 		}
 	}