1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2007-2009 Dag-Erling Smørgrav
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 #include <sys/file.h>
32 #include <sys/stat.h>
33
34 #include <errno.h>
35 #include <stdarg.h>
36 #include <unistd.h>
37
38 #include <libutil.h>
39
40 /*
41 * Reliably open and lock a file.
42 *
43 * Please do not modify this code without first reading the revision history
44 * and discussing your changes with <des@freebsd.org>. Don't be fooled by the
45 * code's apparent simplicity; there would be no need for this function if it
46 * was easy to get right.
47 */
48 static int
vflopenat(int dirfd,const char * path,int flags,va_list ap)49 vflopenat(int dirfd, const char *path, int flags, va_list ap)
50 {
51 int fd, operation, serrno, trunc;
52 struct stat sb, fsb;
53 mode_t mode;
54
55 #ifdef O_EXLOCK
56 flags &= ~O_EXLOCK;
57 #endif
58
59 mode = 0;
60 if (flags & O_CREAT) {
61 mode = (mode_t)va_arg(ap, int); /* mode_t promoted to int */
62 }
63
64 operation = LOCK_EX;
65 if (flags & O_NONBLOCK)
66 operation |= LOCK_NB;
67
68 trunc = (flags & O_TRUNC);
69 flags &= ~O_TRUNC;
70
71 for (;;) {
72 if ((fd = openat(dirfd, path, flags, mode)) == -1)
73 /* non-existent or no access */
74 return (-1);
75 if (flock(fd, operation) == -1) {
76 /* unsupported or interrupted */
77 serrno = errno;
78 (void)close(fd);
79 errno = serrno;
80 return (-1);
81 }
82 if (fstatat(dirfd, path, &sb, 0) == -1) {
83 /* disappeared from under our feet */
84 (void)close(fd);
85 continue;
86 }
87 if (fstat(fd, &fsb) == -1) {
88 /* can't happen [tm] */
89 serrno = errno;
90 (void)close(fd);
91 errno = serrno;
92 return (-1);
93 }
94 if (sb.st_dev != fsb.st_dev ||
95 sb.st_ino != fsb.st_ino) {
96 /* changed under our feet */
97 (void)close(fd);
98 continue;
99 }
100 if (trunc && ftruncate(fd, 0) != 0) {
101 /* can't happen [tm] */
102 serrno = errno;
103 (void)close(fd);
104 errno = serrno;
105 return (-1);
106 }
107 /*
108 * The following change is provided as a specific example to
109 * avoid.
110 */
111 #if 0
112 if (fcntl(fd, F_SETFD, FD_CLOEXEC) != 0) {
113 serrno = errno;
114 (void)close(fd);
115 errno = serrno;
116 return (-1);
117 }
118 #endif
119 return (fd);
120 }
121 }
122
123 int
flopen(const char * path,int flags,...)124 flopen(const char *path, int flags, ...)
125 {
126 va_list ap;
127 int ret;
128
129 va_start(ap, flags);
130 ret = vflopenat(AT_FDCWD, path, flags, ap);
131 va_end(ap);
132 return (ret);
133 }
134
135 int
flopenat(int dirfd,const char * path,int flags,...)136 flopenat(int dirfd, const char *path, int flags, ...)
137 {
138 va_list ap;
139 int ret;
140
141 va_start(ap, flags);
142 ret = vflopenat(dirfd, path, flags, ap);
143 va_end(ap);
144 return (ret);
145 }
146