xref: /freebsd/lib/libc/stdio/fflush.c (revision dc36d6f9)
1 /*-
2  * SPDX-License-Identifier: BSD-3-Clause
3  *
4  * Copyright (c) 1990, 1993
5  *	The Regents of the University of California.  All rights reserved.
6  *
7  * This code is derived from software contributed to Berkeley by
8  * Chris Torek.
9  *
10  * Redistribution and use in source and binary forms, with or without
11  * modification, are permitted provided that the following conditions
12  * are met:
13  * 1. Redistributions of source code must retain the above copyright
14  *    notice, this list of conditions and the following disclaimer.
15  * 2. Redistributions in binary form must reproduce the above copyright
16  *    notice, this list of conditions and the following disclaimer in the
17  *    documentation and/or other materials provided with the distribution.
18  * 3. Neither the name of the University nor the names of its contributors
19  *    may be used to endorse or promote products derived from this software
20  *    without specific prior written permission.
21  *
22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32  * SUCH DAMAGE.
33  */
34 
35 #include "namespace.h"
36 #include <errno.h>
37 #include <stdio.h>
38 #include "un-namespace.h"
39 #include "libc_private.h"
40 #include "local.h"
41 
42 static int	sflush_locked(FILE *);
43 
44 /*
45  * Flush a single file, or (if fp is NULL) all files.
46  * MT-safe version
47  */
48 int
fflush(FILE * fp)49 fflush(FILE *fp)
50 {
51 	int retval;
52 
53 	if (fp == NULL)
54 		return (_fwalk(sflush_locked));
55 	FLOCKFILE_CANCELSAFE(fp);
56 
57 	/*
58 	 * There is disagreement about the correct behaviour of fflush()
59 	 * when passed a file which is not open for writing.  According to
60 	 * the ISO C standard, the behaviour is undefined.
61 	 * Under linux, such an fflush returns success and has no effect;
62 	 * under Windows, such an fflush is documented as behaving instead
63 	 * as fpurge().
64 	 * Given that applications may be written with the expectation of
65 	 * either of these two behaviours, the only safe (non-astonishing)
66 	 * option is to return EBADF and ask that applications be fixed.
67 	 * SUSv3 now requires that fflush() returns success on a read-only
68 	 * stream.
69 	 *
70 	 */
71 	if ((fp->_flags & (__SWR | __SRW)) == 0)
72 		retval = 0;
73 	else
74 		retval = __sflush(fp);
75 	FUNLOCKFILE_CANCELSAFE();
76 	return (retval);
77 }
78 
79 /*
80  * Flush a single file, or (if fp is NULL) all files.
81  * Non-MT-safe version
82  */
83 int
__fflush(FILE * fp)84 __fflush(FILE *fp)
85 {
86 	int retval;
87 
88 	if (fp == NULL)
89 		return (_fwalk(sflush_locked));
90 	if ((fp->_flags & (__SWR | __SRW)) == 0)
91 		retval = 0;
92 	else
93 		retval = __sflush(fp);
94 	return (retval);
95 }
96 
97 __weak_reference(__fflush, fflush_unlocked);
98 
99 int
__sflush(FILE * fp)100 __sflush(FILE *fp)
101 {
102 	unsigned char *p;
103 	int n, f, t;
104 
105 	f = fp->_flags;
106 	if ((f & __SWR) == 0)
107 		return (0);
108 
109 	if ((p = fp->_bf._base) == NULL)
110 		return (0);
111 
112 	n = fp->_p - p;		/* write this much */
113 
114 	/*
115 	 * Set these immediately to avoid problems with longjmp and to allow
116 	 * exchange buffering (via setvbuf) in user write function.
117 	 */
118 	fp->_p = p;
119 	fp->_w = f & (__SLBF|__SNBF) ? 0 : fp->_bf._size;
120 
121 	for (; n > 0; n -= t, p += t) {
122 		t = _swrite(fp, (char *)p, n);
123 		if (t <= 0) {
124 			if (p > fp->_p)
125 				/* Some was written. */
126 				memmove(fp->_p, p, n);
127 			/* Reset _p and _w. */
128 			fp->_p += n;
129 			if ((fp->_flags & __SNBF) == 0)
130 				fp->_w -= n;
131 			fp->_flags |= __SERR;
132 			return (EOF);
133 		}
134 	}
135 	return (0);
136 }
137 
138 static int
sflush_locked(FILE * fp)139 sflush_locked(FILE *fp)
140 {
141 	int	ret;
142 
143 	FLOCKFILE_CANCELSAFE(fp);
144 	ret = __sflush(fp);
145 	FUNLOCKFILE_CANCELSAFE();
146 	return (ret);
147 }
148