diff --git a/libc/stdio/makebuf.c b/libc/stdio/makebuf.c
new file mode 100644
index 0000000..d47e27c
--- /dev/null
+++ b/libc/stdio/makebuf.c
@@ -0,0 +1,107 @@
+/*	$OpenBSD: makebuf.c,v 1.8 2005/12/28 18:50:22 millert 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 <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "local.h"
+
+/*
+ * Allocate a file buffer, or switch to unbuffered I/O.
+ * Per the ANSI C standard, ALL tty devices default to line buffered.
+ *
+ * As a side effect, we set __SOPT or __SNPT (en/dis-able fseek
+ * optimisation) right after the fstat() that finds the buffer size.
+ */
+void
+__smakebuf(FILE *fp)
+{
+	void *p;
+	int flags;
+	size_t size;
+	int couldbetty;
+
+	if (fp->_flags & __SNBF) {
+		fp->_bf._base = fp->_p = fp->_nbuf;
+		fp->_bf._size = 1;
+		return;
+	}
+	flags = __swhatbuf(fp, &size, &couldbetty);
+	if ((p = malloc(size)) == NULL) {
+		fp->_flags |= __SNBF;
+		fp->_bf._base = fp->_p = fp->_nbuf;
+		fp->_bf._size = 1;
+		return;
+	}
+	__atexit_register_cleanup(_cleanup);
+	flags |= __SMBF;
+	fp->_bf._base = fp->_p = p;
+	fp->_bf._size = size;
+	if (couldbetty && isatty(fp->_file))
+		flags |= __SLBF;
+	fp->_flags |= flags;
+}
+
+/*
+ * Internal routine to determine `proper' buffering for a file.
+ */
+int
+__swhatbuf(FILE *fp, size_t *bufsize, int *couldbetty)
+{
+	struct stat st;
+
+	if (fp->_file < 0 || fstat(fp->_file, &st) < 0) {
+		*couldbetty = 0;
+		*bufsize = BUFSIZ;
+		return (__SNPT);
+	}
+
+	/* could be a tty iff it is a character device */
+	*couldbetty = S_ISCHR(st.st_mode);
+	if (st.st_blksize == 0) {
+		*bufsize = BUFSIZ;
+		return (__SNPT);
+	}
+
+	/*
+	 * Optimise fseek() only if it is a regular file.  (The test for
+	 * __sseek is mainly paranoia.)  It is safe to set _blksize
+	 * unconditionally; it will only be used if __SOPT is also set.
+	 */
+	*bufsize = st.st_blksize;
+	fp->_blksize = st.st_blksize;
+	return ((st.st_mode & S_IFMT) == S_IFREG && fp->_seek == __sseek ?
+	    __SOPT : __SNPT);
+}