--- a/ChangeLog	Thu Jun 21 22:45:22 2012 +0200
+++ b/ChangeLog	Fri Jun 22 12:02:54 2012 +0200
@@ -1,3 +1,11 @@
+2012-06-22  Bruno Haible  <bruno@clisp.org>
+
+	fbufmode test: Don't test unportable behaviour.
+	* tests/test-fbufmode.c (test_mode): New function, extracted from main.
+	(main): Invoke it three times.
+	Reported by Szabolcs Nagy <nsz@port70.net>
+	and Rich Felker <dalias@aerifal.cx>.
+
 2012-06-21  Bruno Haible  <bruno@clisp.org>
 
 	gnulib-tool: Refactor inctests variable.

--- a/tests/test-fbufmode.c	Thu Jun 21 22:45:22 2012 +0200
+++ b/tests/test-fbufmode.c	Fri Jun 22 12:02:54 2012 +0200
@@ -26,45 +26,80 @@
 
 #define TESTFILE "t-fbufmode.tmp"
 
-int
-main ()
+/* ISO C99 disallows more than one setvbuf call on a given stream,
+   and HP-UX 11 and musl libc indeed don't support such use of setvbuf.
+   Therefore allocate a new stream for each possible mode value.  */
+static int
+test_mode (int mode)
 {
   FILE *fp;
   char buf[5];
 
-  /* Create a file with some contents.  */
-  fp = fopen (TESTFILE, "w");
-  if (fp == NULL)
-    goto skip;
-  if (fwrite ("foobarsh", 1, 8, fp) < 8)
-    goto skip;
-  if (fclose (fp))
-    goto skip;
-
   /* Open it for reading.  */
   fp = fopen (TESTFILE, "r");
 
-  if (setvbuf (fp, NULL, _IONBF, 0))
-    goto skip;
-  ASSERT (fbufmode (fp) == _IONBF);
+  switch (mode)
+    {
+    case _IONBF:
+      ASSERT (setvbuf (fp, NULL, _IONBF, 0) == 0);
+      ASSERT (fbufmode (fp) == _IONBF);
+      break;
 
-  /* This setvbuf call can fail, e.g. on HP-UX 11.  */
-  if (setvbuf (fp, buf, _IOLBF, 5) == 0)
-    {
+    case _IOLBF:
+      ASSERT (setvbuf (fp, buf, _IOLBF, 5) == 0);
       /* mingw's setvbuf implements _IOLBF the same way as _IOFBF.  */
       ASSERT (fbufmode (fp) == _IOLBF
               || fbufmode (fp) == _IOFBF);
-    }
+      break;
 
-  /* This setvbuf call can fail, e.g. on HP-UX 11.  */
-  if (setvbuf (fp, buf, _IOFBF, 5) == 0)
-    {
+    case _IOFBF:
+      ASSERT (setvbuf (fp, buf, _IOFBF, 5) == 0);
       ASSERT (fbufmode (fp) == _IOFBF);
+      break;
+
+    default:
+      break;
     }
 
   fclose (fp);
 
   return 0;
+}
+
+int
+main ()
+{
+  int ret;
+
+  /* Create a file with some contents.  */
+  {
+    FILE *fp;
+
+    fp = fopen (TESTFILE, "w");
+    if (fp == NULL)
+      goto skip;
+    if (fwrite ("foobarsh", 1, 8, fp) < 8)
+      goto skip;
+    if (fclose (fp))
+      goto skip;
+  }
+
+  ret = test_mode (_IONBF);
+  if (ret != 0)
+    goto fail;
+
+  ret = test_mode (_IOLBF);
+  if (ret != 0)
+    goto fail;
+
+  ret = test_mode (_IOFBF);
+  if (ret != 0)
+    goto fail;
+
+  return 0;
+
+ fail:
+  return ret;
 
  skip:
   fprintf (stderr, "Skipping test: file operations failed.\n");