libutil/flopen.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2007-2009 Dag-Erling Coïdan 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 __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  */
  50 static int
  51 vflopenat(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
 125 int
 126 flopen(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
 137 int
 138 flopenat(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 }