Make exit(), fclose(), fflush(), and freopen() comply with POSIX-2008

requirements for setting the underlying file position when flushing
read-mode streams, and make an fseek()-after-fflush() not change the
underlying file position.

Much testing, review, and assistance from tb@
ok tb@ millert@

8 files changed, 88 insertions, 51 deletions

diff --git a/lib/libc/stdio/fclose.3 b/lib/libc/stdio/fclose.3
index b1f7c536b0a..cedcaed15ed 100644
--- a/lib/libc/stdio/fclose.3
+++ b/lib/libc/stdio/fclose.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: fclose.3,v 1.9 2015/11/04 21:30:13 tedu Exp $
+.\"	$OpenBSD: fclose.3,v 1.10 2024/08/12 20:53:09 guenther Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: November 4 2015 $
+.Dd $Mdocdate: August 12 2024 $
 .Dt FCLOSE 3
 .Os
 .Sh NAME
@@ -47,8 +47,11 @@ The
 function dissociates the named
 .Fa stream
 from its underlying file or set of functions.
-If the stream was being used for output, any buffered data is written
-first, using
+If the stream was being used for output then any buffered data is written
+first,
+while if the stream was being used for input then the underlying
+file position may be updated,
+as if via
 .Xr fflush 3 .
 .Sh RETURN VALUES
 Upon successful completion 0 is returned.
@@ -83,7 +86,7 @@ or
 The
 .Fn fclose
 function conforms to
-.St -ansiC .
+.St -p1003.1-2024 .
 .Sh HISTORY
 The
 .Fn fclose
diff --git a/lib/libc/stdio/fclose.c b/lib/libc/stdio/fclose.c
index 4bd162abc84..07026faccd4 100644
--- a/lib/libc/stdio/fclose.c
+++ b/lib/libc/stdio/fclose.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fclose.c,v 1.10 2015/08/31 02:53:57 guenther Exp $ */
+/*	$OpenBSD: fclose.c,v 1.11 2024/08/12 20:53:09 guenther Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -47,7 +47,7 @@ fclose(FILE *fp)
 	}
 	FLOCKFILE(fp);
 	WCIO_FREE(fp);
-	r = fp->_flags & __SWR ? __sflush(fp) : 0;
+	r = __sflush(fp);
 	if (fp->_close != NULL && (*fp->_close)(fp->_cookie) < 0)
 		r = EOF;
 	if (fp->_flags & __SMBF)
diff --git a/lib/libc/stdio/fflush.3 b/lib/libc/stdio/fflush.3
index 677d087c817..1e1c7803942 100644
--- a/lib/libc/stdio/fflush.3
+++ b/lib/libc/stdio/fflush.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: fflush.3,v 1.13 2019/09/07 10:28:27 schwarze Exp $
+.\"	$OpenBSD: fflush.3,v 1.14 2024/08/12 20:53:09 guenther Exp $
 .\"
 .\" Copyright (c) 1990, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -31,7 +31,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: September 7 2019 $
+.Dd $Mdocdate: August 12 2024 $
 .Dt FFLUSH 3
 .Os
 .Sh NAME
@@ -50,6 +50,20 @@ The function
 forces a write of all buffered data for the given output or update
 .Fa stream
 via the stream's underlying write function.
+If
+.Fa stream
+is a stream opened for reading with
+.Xr fdopen 3 ,
+.Xr fopen 3 ,
+or
+.Xr freopen 3
+of a seekable file and it is not already at EOF then
+.Fn fflush
+sets the seek position of the file to the file position of the
+stream and discards any text pushed back by via
+.Xr ungetc 3 
+or
+.Xr ungetwc 3 .
 The open status of the stream is unaffected.
 .Pp
 If the
@@ -70,7 +84,9 @@ For input streams this discards any input read from the underlying object
 but not yet obtained via
 .Xr getc 3 ;
 this includes any text pushed back via
-.Xr ungetc 3 .
+.Xr ungetc 3
+or
+.Xr ungetwc 3 .
 .Sh RETURN VALUES
 Upon successful completion 0 is returned.
 Otherwise,
@@ -82,9 +98,7 @@ is set to indicate the error.
 .Bl -tag -width Er
 .It Bq Er EBADF
 .Fa stream
-is not an open stream or, in the case of
-.Fn fflush ,
-not a stream open for writing.
+is not an open stream.
 .El
 .Pp
 The function
@@ -102,7 +116,7 @@ for any of the errors specified for the routine
 The
 .Fn fflush
 function conforms to
-.St -ansiC .
+.St -p1003.1-2024 .
 .Sh HISTORY
 A predecessor
 .Fn flush
diff --git a/lib/libc/stdio/fflush.c b/lib/libc/stdio/fflush.c
index fd1a4b3504b..5888e2364c8 100644
--- a/lib/libc/stdio/fflush.c
+++ b/lib/libc/stdio/fflush.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fflush.c,v 1.9 2015/08/31 02:53:57 guenther Exp $ */
+/*	$OpenBSD: fflush.c,v 1.10 2024/08/12 20:53:09 guenther Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -33,6 +33,7 @@
 
 #include <errno.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include "local.h"
 
 /* Flush a single file, or (if fp is NULL) all files.  */
@@ -44,11 +45,7 @@ fflush(FILE *fp)
 	if (fp == NULL)
 		return (_fwalk(__sflush_locked));
 	FLOCKFILE(fp);
-	if ((fp->_flags & (__SWR | __SRW)) == 0) {
-		errno = EBADF;
-		r = EOF;
-	} else
-		r = __sflush(fp);
+	r = __sflush(fp);
 	FUNLOCKFILE(fp);
 	return (r);
 }
@@ -58,30 +55,51 @@ int
 __sflush(FILE *fp)
 {
 	unsigned char *p;
+	fpos_t off;
 	int n, t;
 
 	t = fp->_flags;
-	if ((t & __SWR) == 0)
-		return (0);
+	if (t & __SWR) {
+		if ((p = fp->_bf._base) == NULL)
+			return (0);
 
-	if ((p = fp->_bf._base) == NULL)
-		return (0);
+		n = fp->_p - p;		/* write this much */
 
-	n = fp->_p - p;		/* write this much */
+		/*
+		 * Set these immediately to avoid problems with longjmp and to
+		 * allow exchange buffering (via setvbuf) in user write
+		 * function.
+		 */
+		fp->_p = p;
+		fp->_w = t & (__SLBF|__SNBF) ? 0 : fp->_bf._size;
 
-	/*
-	 * Set these immediately to avoid problems with longjmp and to allow
-	 * exchange buffering (via setvbuf) in user write function.
-	 */
-	fp->_p = p;
-	fp->_w = t & (__SLBF|__SNBF) ? 0 : fp->_bf._size;
+		for (; n > 0; n -= t, p += t) {
+			t = (*fp->_write)(fp->_cookie, (char *)p, n);
+			if (t <= 0) {
+				fp->_flags |= __SERR;
+				return (EOF);
+			}
+		}
+	} else if ((t & __SRD) && !(t & __SEOF)) {
+		if (fp->_seek != __sseek || fp->_file < 0) {
+			errno = EBADF;
+			return EOF;
+		}
 
-	for (; n > 0; n -= t, p += t) {
-		t = (*fp->_write)(fp->_cookie, (char *)p, n);
-		if (t <= 0) {
-			fp->_flags |= __SERR;
-			return (EOF);
+		off = fp->_r;
+		if (HASUB(fp)) {
+			off += fp->_ur;
+			FREEUB(fp);
 		}
+		if (t & __SOFF) {
+			off = fp->_offset - off;
+			__sseek(fp->_cookie, off, SEEK_SET);
+		} else if (off != 0)
+			__sseek(fp->_cookie, -off, SEEK_CUR);
+
+		WCIO_FREE(fp);
+		fp->_p = fp->_bf._base;
+		fp->_r = 0;
 	}
 	return (0);
 }
diff --git a/lib/libc/stdio/freopen.c b/lib/libc/stdio/freopen.c
index 65065e54d7d..2b82300c0b2 100644
--- a/lib/libc/stdio/freopen.c
+++ b/lib/libc/stdio/freopen.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: freopen.c,v 1.17 2019/06/29 16:12:21 deraadt Exp $ */
+/*	$OpenBSD: freopen.c,v 1.18 2024/08/12 20:53:09 guenther Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -75,9 +75,8 @@ freopen(const char *file, const char *mode, FILE *fp)
 		isopen = 0;
 		wantfd = -1;
 	} else {
-		/* flush the stream; ANSI doesn't require this. */
-		if (fp->_flags & __SWR)
-			(void) __sflush(fp);
+		/* flush the stream; POSIX, not ANSI, requires this. */
+		(void) __sflush(fp);
 		/* if close is NULL, closing is a no-op, hence pointless */
 		isopen = fp->_close != NULL;
 		if ((wantfd = fp->_file) < 0 && isopen) {
diff --git a/lib/libc/stdio/fseek.c b/lib/libc/stdio/fseek.c
index 18c530138a6..a65867d3f46 100644
--- a/lib/libc/stdio/fseek.c
+++ b/lib/libc/stdio/fseek.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: fseek.c,v 1.14 2022/05/14 05:06:32 guenther Exp $ */
+/*	$OpenBSD: fseek.c,v 1.15 2024/08/12 20:53:09 guenther Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -116,7 +116,8 @@ fseeko(FILE *fp, off_t offset, int whence)
 	/*
 	 * Can only optimise if:
 	 *	reading (and not reading-and-writing);
-	 *	not unbuffered; and
+	 *	not unbuffered;
+	 *	not immediately after an fflush(); and
 	 *	this is a `regular' Unix file (and hence seekfn==__sseek).
 	 * We must check __NBF first, because it is possible to have __NBF
 	 * and __SOPT both set.
@@ -125,6 +126,8 @@ fseeko(FILE *fp, off_t offset, int whence)
 		__smakebuf(fp);
 	if (fp->_flags & (__SWR | __SRW | __SNBF | __SNPT))
 		goto dumb;
+	if (fp->_r == 0 && (fp->_p == NULL || fp->_p == fp->_bf._base))
+		goto dumb;
 	if ((fp->_flags & __SOPT) == 0) {
 		if (seekfn != __sseek ||
 		    fp->_file < 0 || fstat(fp->_file, &st) == -1 ||
@@ -228,7 +231,7 @@ fseeko(FILE *fp, off_t offset, int whence)
 	 * do it.  Allow the seek function to change fp->_bf._base.
 	 */
 dumb:
-	if (__sflush(fp) ||
+	if (((fp->_flags & __SWR) && __sflush(fp)) ||
 	    (*seekfn)(fp->_cookie, (fpos_t)offset, whence) == POS_ERR) {
 		FUNLOCKFILE(fp);
 		return (EOF);
diff --git a/lib/libc/stdio/ftell.c b/lib/libc/stdio/ftell.c
index a75ebbbaad7..69e1f0d6ef9 100644
--- a/lib/libc/stdio/ftell.c
+++ b/lib/libc/stdio/ftell.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: ftell.c,v 1.11 2015/08/31 02:53:57 guenther Exp $ */
+/*	$OpenBSD: ftell.c,v 1.12 2024/08/12 20:53:09 guenther Exp $ */
 /*-
  * Copyright (c) 1990, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -55,7 +55,8 @@ ftello(FILE *fp)
 	 * adjust for buffered bytes.
 	 */
 	FLOCKFILE(fp);
-	__sflush(fp);		/* may adjust seek offset on append stream */
+	if (fp->_flags & __SWR)
+		__sflush(fp);	/* may adjust seek offset on append stream */
 	if (fp->_flags & __SOFF)
 		pos = fp->_offset;
 	else {
diff --git a/lib/libc/stdlib/exit.3 b/lib/libc/stdlib/exit.3
index a1c43780d65..5e006e53f40 100644
--- a/lib/libc/stdlib/exit.3
+++ b/lib/libc/stdlib/exit.3
@@ -29,9 +29,9 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.\"	$OpenBSD: exit.3,v 1.16 2014/11/30 21:21:59 schwarze Exp $
+.\"	$OpenBSD: exit.3,v 1.17 2024/08/12 20:53:09 guenther Exp $
 .\"
-.Dd $Mdocdate: November 30 2014 $
+.Dd $Mdocdate: August 12 2024 $
 .Dt EXIT 3
 .Os
 .Sh NAME
@@ -54,9 +54,7 @@ Call the functions registered with the
 .Xr atexit 3
 function, in the reverse order of their registration.
 .It
-Flush all open output streams.
-.It
-Close all open streams.
+Flush and close all open streams.
 .It
 Unlink all files created with the
 .Xr tmpfile 3
@@ -79,6 +77,7 @@ function never returns.
 .Sh SEE ALSO
 .Xr _exit 2 ,
 .Xr atexit 3 ,
+.Xr fflush 3 ,
 .Xr intro 3 ,
 .Xr sysexits 3 ,
 .Xr tmpfile 3
@@ -86,7 +85,7 @@ function never returns.
 The
 .Fn exit
 function conforms to
-.St -isoC-99 .
+.St -p1003.1-2024 .
 .Sh HISTORY
 An
 .Fn exit