libutil/flopen.c

   1 /*-
   2  * Copyright (c) 2007 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 <fcntl.h>
  36 #include <stdarg.h>
  37 #include <unistd.h>
  38
  39 #include <libutil.h>
  40
  41 int
  42 flopen(const char *path, int flags, ...)
  43 {
  44         int fd, operation, serrno, truncate;
  45         struct stat sb, fsb;
  46         mode_t mode;
  47
  48 #ifdef O_EXLOCK
  49         flags &= ~O_EXLOCK;
  50 #endif
  51
  52         mode = 0;
  53         if (flags & O_CREAT) {
  54                 va_list ap;
  55
  56                 va_start(ap, flags);
  57                 mode = va_arg(ap, int); /* mode_t promoted to int */
  58                 va_end(ap);
  59         }
  60
  61         operation = LOCK_EX;
  62         if (flags & O_NONBLOCK)
  63                 operation |= LOCK_NB;
  64
  65         truncate = (flags & O_TRUNC);
  66         flags &= ~O_TRUNC;
  67
  68         for (;;) {
  69                 if ((fd = open(path, flags, mode)) == -1)
  70                         /* non-existent or no access */
  71                         return (-1);
  72                 if (flock(fd, operation) == -1) {
  73                         /* unsupported or interrupted */
  74                         serrno = errno;
  75                         close(fd);
  76                         errno = serrno;
  77                         return (-1);
  78                 }
  79                 if (stat(path, &sb) == -1) {
  80                         /* disappeared from under our feet */
  81                         close(fd);
  82                         continue;
  83                 }
  84                 if (fstat(fd, &fsb) == -1) {
  85                         /* can't happen [tm] */
  86                         serrno = errno;
  87                         close(fd);
  88                         errno = serrno;
  89                         return (-1);
  90                 }
  91                 if (sb.st_dev != fsb.st_dev ||
  92                     sb.st_ino != fsb.st_ino) {
  93                         /* changed under our feet */
  94                         close(fd);
  95                         continue;
  96                 }
  97                 if (truncate && ftruncate(fd, 0) != 0) {
  98                         /* can't happen [tm] */
  99                         serrno = errno;
 100                         close(fd);
 101                         errno = serrno;
 102                         return (-1);
 103                 }
 104                 return (fd);
 105         }
 106 }