lib/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  * $FreeBSD: head/lib/libutil/flopen.c 193591 2009-06-06 18:47:03Z des $
  28  */
  29
  30 #include <sys/stat.h>
  31
  32 #include <errno.h>
  33 #include <stdarg.h>
  34 #include <unistd.h>
  35 #include <fcntl.h>
  36 #include <libutil.h>
  37
  38 int
  39 flopen(const char *path, int flags, ...)
  40 {
  41         int fd, operation, serrno, trunc;
  42         struct stat sb, fsb;
  43         mode_t mode;
  44
  45 #ifdef O_EXLOCK
  46         flags &= ~O_EXLOCK;
  47 #endif
  48
  49         mode = 0;
  50         if (flags & O_CREAT) {
  51                 va_list ap;
  52
  53                 va_start(ap, flags);
  54                 mode = (mode_t)va_arg(ap, int); /* mode_t promoted to int */
  55                 va_end(ap);
  56         }
  57
  58         operation = LOCK_EX;
  59         if (flags & O_NONBLOCK)
  60                 operation |= LOCK_NB;
  61
  62         trunc = (flags & O_TRUNC);
  63         flags &= ~O_TRUNC;
  64
  65         for (;;) {
  66                 if ((fd = open(path, flags, mode)) == -1)
  67                         /* non-existent or no access */
  68                         return (-1);
  69                 if (flock(fd, operation) == -1) {
  70                         /* unsupported or interrupted */
  71                         serrno = errno;
  72                         (void)close(fd);
  73                         errno = serrno;
  74                         return (-1);
  75                 }
  76                 if (stat(path, &sb) == -1) {
  77                         /* disappeared from under our feet */
  78                         (void)close(fd);
  79                         continue;
  80                 }
  81                 if (fstat(fd, &fsb) == -1) {
  82                         /* can't happen [tm] */
  83                         serrno = errno;
  84                         (void)close(fd);
  85                         errno = serrno;
  86                         return (-1);
  87                 }
  88                 if (sb.st_dev != fsb.st_dev ||
  89                     sb.st_ino != fsb.st_ino) {
  90                         /* changed under our feet */
  91                         (void)close(fd);
  92                         continue;
  93                 }
  94                 if (trunc && ftruncate(fd, 0) != 0) {
  95                         /* can't happen [tm] */
  96                         serrno = errno;
  97                         (void)close(fd);
  98                         errno = serrno;
  99                         return (-1);
 100                 }
 101                 return (fd);
 102         }
 103 }