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: src/lib/libutil/flopen.c,v 1.11 2008/10/20 18:11:30 des Exp $
  28  */
  29
  30 #include <sys/stat.h>
  31
  32 #include <errno.h>
  33 #include <fcntl.h>
  34 #include <stdarg.h>
  35 #include <string.h>
  36 #include <unistd.h>
  37
  38 #include <libutil.h>
  39
  40 int
  41 flopen(const char *path, int flags, ...)
  42 {
  43         int fd, operation, serrno, trunc;
  44         struct flock lock;
  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 = (mode_t)va_arg(ap, int); /* mode_t promoted to int */
  58                 va_end(ap);
  59         }
  60
  61         memset(&lock, 0, sizeof lock);
  62         lock.l_type = ((flags & O_ACCMODE) == O_RDONLY) ? F_RDLCK : F_WRLCK;
  63         lock.l_whence = SEEK_SET;
  64         operation = (flags & O_NONBLOCK) ? F_SETLK : F_SETLKW;
  65
  66         trunc = (flags & O_TRUNC);
  67         flags &= ~O_TRUNC;
  68
  69         for (;;) {
  70                 if ((fd = open(path, flags, mode)) == -1)
  71                         /* non-existent or no access */
  72                         return (-1);
  73                 if (fcntl(fd, operation, &lock) == -1) {
  74                         /* unsupported or interrupted */
  75                         serrno = errno;
  76                         close(fd);
  77                         errno = serrno;
  78                         return (-1);
  79                 }
  80                 if (stat(path, &sb) == -1) {
  81                         /* disappeared from under our feet */
  82                         close(fd);
  83                         continue;
  84                 }
  85                 if (fstat(fd, &fsb) == -1) {
  86                         /* can't happen [tm] */
  87                         serrno = errno;
  88                         close(fd);
  89                         errno = serrno;
  90                         return (-1);
  91                 }
  92                 if (sb.st_dev != fsb.st_dev ||
  93                     sb.st_ino != fsb.st_ino) {
  94                         /* changed under our feet */
  95                         close(fd);
  96                         continue;
  97                 }
  98                 if (trunc && ftruncate(fd, 0) != 0) {
  99                         /* can't happen [tm] */
 100                         serrno = errno;
 101                         close(fd);
 102                         errno = serrno;
 103                         return (-1);
 104                 }
 105                 return (fd);
 106         }
 107 }