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 int 49 flopen(const char *path, int flags, ...) 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 va_list ap; 62 63 va_start(ap, flags); 64 mode = (mode_t)va_arg(ap, int); /* mode_t promoted to int */ 65 va_end(ap); 66 } 67 68 operation = LOCK_EX; 69 if (flags & O_NONBLOCK) 70 operation |= LOCK_NB; 71 72 trunc = (flags & O_TRUNC); 73 flags &= ~O_TRUNC; 74 75 for (;;) { 76 if ((fd = open(path, flags, mode)) == -1) 77 /* non-existent or no access */ 78 return (-1); 79 if (flock(fd, operation) == -1) { 80 /* unsupported or interrupted */ 81 serrno = errno; 82 (void)close(fd); 83 errno = serrno; 84 return (-1); 85 } 86 if (stat(path, &sb) == -1) { 87 /* disappeared from under our feet */ 88 (void)close(fd); 89 continue; 90 } 91 if (fstat(fd, &fsb) == -1) { 92 /* can't happen [tm] */ 93 serrno = errno; 94 (void)close(fd); 95 errno = serrno; 96 return (-1); 97 } 98 if (sb.st_dev != fsb.st_dev || 99 sb.st_ino != fsb.st_ino) { 100 /* changed under our feet */ 101 (void)close(fd); 102 continue; 103 } 104 if (trunc && ftruncate(fd, 0) != 0) { 105 /* can't happen [tm] */ 106 serrno = errno; 107 (void)close(fd); 108 errno = serrno; 109 return (-1); 110 } 111 /* 112 * The following change is provided as a specific example to 113 * avoid. 114 */ 115 #if 0 116 if (fcntl(fd, F_SETFD, FD_CLOEXEC) != 0) { 117 serrno = errno; 118 (void)close(fd); 119 errno = serrno; 120 return (-1); 121 } 122 #endif 123 return (fd); 124 } 125 } 126