One thing that has bugged me for years is that pax/tar fully buffers
the file list output when used in a pipeline.  For example, given:

    $ tar cf - * | ssh otherhost "tar vxf -"

the file list output will all be displayed at the end instead of
as the files are written.  If the list file handle is not stderr,
making it line buffered fixes this.

 - todd

Index: bin/pax/cpio.c
===================================================================
RCS file: /cvs/src/bin/pax/cpio.c,v
diff -u -p -u -r1.114 options.c
--- bin/pax/options.c	17 Apr 2024 18:12:12 -0000	1.114
+++ bin/pax/options.c	10 May 2024 18:38:02 -0000
@@ -277,21 +277,20 @@ options(int argc, char **argv)
 	if (strcmp(NM_TAR, argv0) == 0) {
 		op_mode = OP_TAR;
 		tar_options(argc, argv);
-		return;
-	}
 #ifndef NOCPIO
-	else if (strcmp(NM_CPIO, argv0) == 0) {
+	} else if (strcmp(NM_CPIO, argv0) == 0) {
 		op_mode = OP_CPIO;
 		cpio_options(argc, argv);
-		return;
-	}
 #endif /* !NOCPIO */
-	/*
-	 * assume pax as the default
-	 */
-	argv0 = NM_PAX;
-	op_mode = OP_PAX;
-	pax_options(argc, argv);
+	} else {
+		argv0 = NM_PAX;
+		op_mode = OP_PAX;
+		pax_options(argc, argv);
+	}
+
+	/* Line-buffer the file list output as needed. */
+	if (listf != stderr)
+		setvbuf(listf, NULL, _IOLBF, 0);
 }
 
 /*