diff --git a/libc/stdio/setvbuf.c b/libc/stdio/setvbuf.c
new file mode 100644
index 0000000..9b92bf0
--- /dev/null
+++ b/libc/stdio/setvbuf.c
@@ -0,0 +1,151 @@
+/*	$OpenBSD: setvbuf.c,v 1.8 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"
+
+/*
+ * Set one of the three kinds of buffering, optionally including
+ * a buffer.
+ */
+int
+setvbuf(FILE *fp, char *buf, int mode, size_t size)
+{
+	int ret, flags;
+	size_t iosize;
+	int ttyflag;
+
+	/*
+	 * Verify arguments.  The `int' limit on `size' is due to this
+	 * particular implementation.  Note, buf and size are ignored
+	 * when setting _IONBF.
+	 */
+	if (mode != _IONBF)
+		if ((mode != _IOFBF && mode != _IOLBF) || (int)size < 0)
+			return (EOF);
+
+	/*
+	 * Write current buffer, if any.  Discard unread input (including
+	 * ungetc data), cancel line buffering, and free old buffer if
+	 * malloc()ed.  We also clear any eof condition, as if this were
+	 * a seek.
+	 */
+	ret = 0;
+	(void)__sflush(fp);
+	if (HASUB(fp))
+		FREEUB(fp);
+	WCIO_FREE(fp);
+	fp->_r = fp->_lbfsize = 0;
+	flags = fp->_flags;
+	if (flags & __SMBF)
+		free((void *)fp->_bf._base);
+	flags &= ~(__SLBF | __SNBF | __SMBF | __SOPT | __SNPT | __SEOF);
+
+	/* If setting unbuffered mode, skip all the hard work. */
+	if (mode == _IONBF)
+		goto nbf;
+
+	/*
+	 * Find optimal I/O size for seek optimization.  This also returns
+	 * a `tty flag' to suggest that we check isatty(fd), but we do not
+	 * care since our caller told us how to buffer.
+	 */
+	flags |= __swhatbuf(fp, &iosize, &ttyflag);
+	if (size == 0) {
+		buf = NULL;	/* force local allocation */
+		size = iosize;
+	}
+
+	/* Allocate buffer if needed. */
+	if (buf == NULL) {
+		if ((buf = malloc(size)) == NULL) {
+			/*
+			 * Unable to honor user's request.  We will return
+			 * failure, but try again with file system size.
+			 */
+			ret = EOF;
+			if (size != iosize) {
+				size = iosize;
+				buf = malloc(size);
+			}
+		}
+		if (buf == NULL) {
+			/* No luck; switch to unbuffered I/O. */
+nbf:
+			fp->_flags = flags | __SNBF;
+			fp->_w = 0;
+			fp->_bf._base = fp->_p = fp->_nbuf;
+			fp->_bf._size = 1;
+			return (ret);
+		}
+		flags |= __SMBF;
+	}
+
+	/*
+	 * Kill any seek optimization if the buffer is not the
+	 * right size.
+	 *
+	 * SHOULD WE ALLOW MULTIPLES HERE (i.e., ok iff (size % iosize) == 0)?
+	 */
+	if (size != iosize)
+		flags |= __SNPT;
+
+	/*
+	 * Fix up the FILE fields, and set __cleanup for output flush on
+	 * exit (since we are buffered in some way).
+	 */
+	if (mode == _IOLBF)
+		flags |= __SLBF;
+	fp->_flags = flags;
+	fp->_bf._base = fp->_p = (unsigned char *)buf;
+	fp->_bf._size = size;
+	/* fp->_lbfsize is still 0 */
+	if (flags & __SWR) {
+		/*
+		 * Begin or continue writing: see __swsetup().  Note
+		 * that __SNBF is impossible (it was handled earlier).
+		 */
+		if (flags & __SLBF) {
+			fp->_w = 0;
+			fp->_lbfsize = -fp->_bf._size;
+		} else
+			fp->_w = size;
+	} else {
+		/* begin/continue reading, or stay in intermediate state */
+		fp->_w = 0;
+	}
+	__atexit_register_cleanup(_cleanup);
+
+	return (ret);
+}