auto import from //depot/cupcake/@135843
diff --git a/libc/stdio/wsetup.c b/libc/stdio/wsetup.c
new file mode 100644
index 0000000..0834223
--- /dev/null
+++ b/libc/stdio/wsetup.c
@@ -0,0 +1,86 @@
+/* $OpenBSD: wsetup.c,v 1.7 2005/08/08 08:05:36 espie Exp $ */
+/*-
+ * Copyright (c) 1990, 1993
+ * The Regents of the University of California. All rights reserved.
+ *
+ * This code is derived from software contributed to Berkeley by
+ * Chris Torek.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include "local.h"
+
+/*
+ * 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.
+ */
+int
+__swsetup(FILE *fp)
+{
+ /* make sure stdio is set up */
+ if (!__sdidinit)
+ __sinit();
+
+ /*
+ * If we are not writing, we had better be reading and writing.
+ */
+ if ((fp->_flags & __SWR) == 0) {
+ if ((fp->_flags & __SRW) == 0)
+ return (EOF);
+ if (fp->_flags & __SRD) {
+ /* clobber any ungetc data */
+ if (HASUB(fp))
+ FREEUB(fp);
+ fp->_flags &= ~(__SRD|__SEOF);
+ fp->_r = 0;
+ fp->_p = fp->_bf._base;
+ }
+ fp->_flags |= __SWR;
+ }
+
+ /*
+ * Make a buffer if necessary, then set _w.
+ */
+ if (fp->_bf._base == NULL) {
+ if ((fp->_flags & (__SSTR | __SALC)) == __SSTR)
+ return (EOF);
+ __smakebuf(fp);
+ }
+ if (fp->_flags & __SLBF) {
+ /*
+ * It is line buffered, so make _lbfsize be -_bufsize
+ * for the putc() macro. We will change _lbfsize back
+ * to 0 whenever we turn off __SWR.
+ */
+ fp->_w = 0;
+ fp->_lbfsize = -fp->_bf._size;
+ } else
+ fp->_w = fp->_flags & __SNBF ? 0 : fp->_bf._size;
+ return (0);
+}