Simplify the cleanup before downloading

Since renaming the existing (reuse failed) file to the tmp file
then asking the sync function to reuse it again introduces more
potential errors with little gain, we decide to directly do clean
up if the 1st reusage fails.

Signed-off-by: Shuo Wu <shuo.wu@suse.com>

pkg/server/backing_image.go

@@ -368,36 +368,12 @@ func (bi *BackingImage) checkAndReuseBackingImageFileWithoutLock() error {
 }
 
 func (bi *BackingImage) prepareForDownload() error {
-	if _, err := os.Stat(bi.WorkDirectory); os.IsNotExist(err) {
-		if err := os.Mkdir(bi.WorkDirectory, 666); err != nil {
-			return errors.Wrapf(err, "failed to create work directory %v before downloading", bi.WorkDirectory)
-		}
-		return nil
+	if err := os.RemoveAll(bi.WorkDirectory); err != nil {
+		return errors.Wrapf(err, "failed to clean up the work directory %v before downloading", bi.WorkDirectory)
 	}
-
-	configFilePath := filepath.Join(bi.WorkDirectory, util.BackingImageConfigFile)
-	if err := os.Remove(configFilePath); err != nil && !os.IsNotExist(err) {
-		return err
+	if err := os.Mkdir(bi.WorkDirectory, 666); err != nil && !os.IsExist(err) {
+		return errors.Wrapf(err, "failed to create work directory %v before downloading", bi.WorkDirectory)
 	}
-
-	// By renaming the existing backing image file to the tmp file, the sync function can reuse part of the data
-	backingImageTmpPath := filepath.Join(bi.WorkDirectory, types.BackingImageTmpFileName)
-	backingImagePath := filepath.Join(bi.WorkDirectory, types.BackingImageFileName)
-	if _, err := os.Stat(backingImagePath); os.IsExist(err) {
-		if _, err := os.Stat(backingImageTmpPath); os.IsExist(err) {
-			if err := os.Remove(backingImageTmpPath); err != nil {
-				return errors.Wrapf(err, "failed to delete tmp file %v before trying to reuse file %v", backingImageTmpPath, backingImagePath)
-			}
-		}
-		if err := os.Rename(backingImagePath, backingImageTmpPath); err != nil {
-			bi.log.WithError(err).Warnf("Backing Image: failed to rename existing file %v to tmp file %v before trying to reuse it, will fall back to clean up it", backingImagePath, backingImageTmpPath)
-			if err := os.Remove(backingImagePath); err != nil {
-				return errors.Wrapf(err, "failed to delete file %v before downloading", backingImagePath)
-			}
-		}
-		return nil
-	}
-
 	return nil
 }