1/*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright (c) 2007-2009 Dag-Erling Co��dan Sm��rgrav
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 *    notice, this list of conditions and the following disclaimer
12 *    in this position and unchanged.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30#include <sys/cdefs.h>
31__FBSDID("$FreeBSD$");
32
33#include <sys/file.h>
34#include <sys/stat.h>
35
36#include <errno.h>
37#include <stdarg.h>
38#include <unistd.h>
39
40#include <libutil.h>
41
42/*
43 * Reliably open and lock a file.
44 *
45 * Please do not modify this code without first reading the revision history
46 * and discussing your changes with <des@freebsd.org>.  Don't be fooled by the
47 * code's apparent simplicity; there would be no need for this function if it
48 * was easy to get right.
49 */
50static int
51vflopenat(int dirfd, const char *path, int flags, va_list ap)
52{
53	int fd, operation, serrno, trunc;
54	struct stat sb, fsb;
55	mode_t mode;
56
57#ifdef O_EXLOCK
58	flags &= ~O_EXLOCK;
59#endif
60
61	mode = 0;
62	if (flags & O_CREAT) {
63		mode = (mode_t)va_arg(ap, int); /* mode_t promoted to int */
64	}
65
66        operation = LOCK_EX;
67        if (flags & O_NONBLOCK)
68                operation |= LOCK_NB;
69
70	trunc = (flags & O_TRUNC);
71	flags &= ~O_TRUNC;
72
73	for (;;) {
74		if ((fd = openat(dirfd, path, flags, mode)) == -1)
75			/* non-existent or no access */
76			return (-1);
77		if (flock(fd, operation) == -1) {
78			/* unsupported or interrupted */
79			serrno = errno;
80			(void)close(fd);
81			errno = serrno;
82			return (-1);
83		}
84		if (fstatat(dirfd, path, &sb, 0) == -1) {
85			/* disappeared from under our feet */
86			(void)close(fd);
87			continue;
88		}
89		if (fstat(fd, &fsb) == -1) {
90			/* can't happen [tm] */
91			serrno = errno;
92			(void)close(fd);
93			errno = serrno;
94			return (-1);
95		}
96		if (sb.st_dev != fsb.st_dev ||
97		    sb.st_ino != fsb.st_ino) {
98			/* changed under our feet */
99			(void)close(fd);
100			continue;
101		}
102		if (trunc && ftruncate(fd, 0) != 0) {
103			/* can't happen [tm] */
104			serrno = errno;
105			(void)close(fd);
106			errno = serrno;
107			return (-1);
108		}
109		/*
110		 * The following change is provided as a specific example to
111		 * avoid.
112		 */
113#if 0
114		if (fcntl(fd, F_SETFD, FD_CLOEXEC) != 0) {
115			serrno = errno;
116			(void)close(fd);
117			errno = serrno;
118			return (-1);
119		}
120#endif
121		return (fd);
122	}
123}
124
125int
126flopen(const char *path, int flags, ...)
127{
128	va_list ap;
129	int ret;
130
131	va_start(ap, flags);
132	ret = vflopenat(AT_FDCWD, path, flags, ap);
133	va_end(ap);
134	return (ret);
135}
136
137int
138flopenat(int dirfd, const char *path, int flags, ...)
139{
140	va_list ap;
141	int ret;
142
143	va_start(ap, flags);
144	ret = vflopenat(dirfd, path, flags, ap);
145	va_end(ap);
146	return (ret);
147}
148