diff --git a/libc/stdio/flags.c b/libc/stdio/flags.c
new file mode 100644
index 0000000..dde0447
--- /dev/null
+++ b/libc/stdio/flags.c
@@ -0,0 +1,82 @@
+/*	$OpenBSD: flags.c,v 1.6 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 <sys/types.h>
+#include <sys/file.h>
+#include <stdio.h>
+#include <errno.h>
+#include <fcntl.h>
+
+/*
+ * Return the (stdio) flags for a given mode.  Store the flags
+ * to be passed to an open() syscall through *optr.
+ * Return 0 on error.
+ */
+int
+__sflags(const char *mode, int *optr)
+{
+	int ret, m, o;
+
+	switch (*mode++) {
+
+	case 'r':	/* open for reading */
+		ret = __SRD;
+		m = O_RDONLY;
+		o = 0;
+		break;
+
+	case 'w':	/* open for writing */
+		ret = __SWR;
+		m = O_WRONLY;
+		o = O_CREAT | O_TRUNC;
+		break;
+
+	case 'a':	/* open for appending */
+		ret = __SWR;
+		m = O_WRONLY;
+		o = O_CREAT | O_APPEND;
+		break;
+
+	default:	/* illegal mode */
+		errno = EINVAL;
+		return (0);
+	}
+
+	/* [rwa]\+ or [rwa]b\+ means read and write */
+	if (*mode == '+' || (*mode == 'b' && mode[1] == '+')) {
+		ret = __SRW;
+		m = O_RDWR;
+	}
+	*optr = m | o;
+	return (ret);
+}