fix fputc and friends on read-only streams

[Eric Blake]

POSIX requires that ferror() and errno reflect any failed attempt to
write to a read-only stream, but newlib wasn't reliably doing this:

#include <stdio.h>
#include <errno.h>
int main()
{
  FILE *f = fopen ("f", "w");
  if (!f)
    return 1;
  if (freopen ("f", "r", f) != f)
    return 2;
  if (setvbuf (f, NULL, _IONBF, BUFSIZ))
    return 3;
  if (ferror (f))
    return 4;
  errno = -1;
  if (fprintf (f, "hi") != EOF)
    return 5;
  if (errno <= 0)
    return 6;
  if (!ferror (f))
    return 7;
  if (fclose (f))
    return 8;
  if (remove (f))
    return 9;
  return 0;
}

This was mistakenly existing with status 6; comment that line out and it
exited with status 7.  This fix mirrors the refill.c setting of errors
on attempts to read a write-only stream.

---
 newlib/ChangeLog           |    4 ++++
 newlib/libc/stdio/wsetup.c |    6 +++++-
 2 files changed, 9 insertions(+), 1 deletions(-)

2011-06-07  Eric Blake  <eblake@redhat.com>

	* libc/stdio/wsetup.c (__swsetup_r): Set errno on failure.

diff --git a/newlib/libc/stdio/wsetup.c b/newlib/libc/stdio/wsetup.c
index dcbda0a..6513e00 100644
--- a/newlib/libc/stdio/wsetup.c
+++ b/newlib/libc/stdio/wsetup.c
@@ -44,7 +44,11 @@ _DEFUN(__swsetup_r, (ptr, fp),
   if ((fp->_flags & __SWR) == 0)
     {
       if ((fp->_flags & __SRW) == 0)
-	return EOF;
+        {
+          ptr->_errno = EBADF;
+          fp->_flags |= __SERR;
+          return EOF;
+        }
       if (fp->_flags & __SRD)
 	{
 	  /* clobber any ungetc data */
-- 
1.7.5.1


-- 
Eric Blake   eblake@redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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