OCPBUGS-60273: Ensure revision.json persists on ungraceful shutdown

Add os.O_SYNC flag to OpenFile call in trySaveRevision to force
synchronous writes to disk. This prevents the revision.json file from
being empty if the process terminates unexpectedly before buffered data
is flushed.

Author: clobrano

pkg/cmd/rev/rev.go

@@ -189,14 +189,24 @@ func trySaveRevision(ctx context.Context, endpoints []string, outputFile string,
 	}
 
 	tmpPath := fmt.Sprintf("%s.tmp", outputFile)
-	file, err := os.OpenFile(tmpPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	file, err := os.OpenFile(tmpPath, os.O_CREATE|os.O_WRONLY|os.O_TRUNC|os.O_SYNC, 0644)
 	if err != nil {
 		klog.Errorf("error opening file: %v", err)
 		return
 	}
 	defer func() {
-		if err = file.Close(); err != nil {
-			klog.Errorf("error closing file: %v", err)
+		if closeErr := file.Close(); closeErr != nil {
+			klog.Errorf("error closing file: %v", closeErr)
+			return
+		}
+		// Only rename if no error occurred before
+		if err != nil {
+			klog.Errorf("could not create temporary revision.json, keeping current version: %v", err)
+			return
+		}
+		if err = os.Rename(tmpPath, outputFile); err != nil {
+			klog.Errorf("error during rename to destination file: %v", err)
+			return
 		}
 	}()
 
@@ -205,11 +215,6 @@ func trySaveRevision(ctx context.Context, endpoints []string, outputFile string,
 		klog.Errorf("error writing result to file: %v", err)
 		return
 	}
-
-	if err = os.Rename(tmpPath, outputFile); err != nil {
-		klog.Errorf("error during rename to destination file: %v", err)
-		return
-	}
 }
 
 func newETCD3Client(ctx context.Context, endpoints []string, tlsInfo transport.TLSInfo) (*clientv3.Client, error) {