xref: /freebsd/lib/libutil/flopen.c (revision da3086df1863e9aed45eb14e265c306f8bb27d80)
1 /*-
2  * Copyright (c) 2007-2009 Dag-Erling Coïdan Smørgrav
3  * All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions
7  * are met:
8  * 1. Redistributions of source code must retain the above copyright
9  *    notice, this list of conditions and the following disclaimer
10  *    in this position and unchanged.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in the
13  *    documentation and/or other materials provided with the distribution.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25  * SUCH DAMAGE.
26  */
27 
28 #include <sys/cdefs.h>
29 __FBSDID("$FreeBSD$");
30 
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
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
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
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