Set errno to EBADF on attempts to write to a stream that is not

writable.  Affected callers include fwrite(), put?(), and *printf().
The issue of whether this is the right errno for funopened streams is
unresolved, but that's an obscure case, and some errno is better than
no errno.

Discussed with:	bde, jkh

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/libc/stdio/wsetup.c b/lib/libc/stdio/wsetup.c
index 4039a11..4c18dd4 100644
--- a/lib/libc/stdio/wsetup.c
+++ b/lib/libc/stdio/wsetup.c
@@ -40,6 +40,7 @@ static char sccsid[] = "@(#)wsetup.c	8.1 (Berkeley) 6/4/93";
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <errno.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include "local.h"
@@ -47,7 +48,7 @@ __FBSDID("$FreeBSD$");
 /*
  * Various output routines call wsetup to be sure it is safe to write,
  * because either _flags does not include __SWR, or _buf is NULL.
- * _wsetup returns 0 if OK to write, nonzero otherwise.
+ * _wsetup returns 0 if OK to write; otherwise, it returns EOF and sets errno.
  */
 int
 __swsetup(fp)
@@ -61,8 +62,10 @@ __swsetup(fp)
 	 * If we are not writing, we had better be reading and writing.
 	 */
 	if ((fp->_flags & __SWR) == 0) {
-		if ((fp->_flags & __SRW) == 0)
+		if ((fp->_flags & __SRW) == 0) {
+			errno = EBADF;
 			return (EOF);
+		}
 		if (fp->_flags & __SRD) {
 			/* clobber any ungetc data */
 			if (HASUB(fp))