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, trunc;
  45         struct stat sb, fsb;
  46         struct flock lock;
  47         mode_t mode;
  48
  49 #ifdef O_EXLOCK
  50         flags &= ~O_EXLOCK;
  51 #endif
  52
  53         mode = 0;
  54         if (flags & O_CREAT) {
  55                 va_list ap;
  56
  57                 va_start(ap, flags);
  58                 mode = va_arg(ap, int); /* mode_t promoted to int */
  59                 va_end(ap);
  60         }
  61
  62         lock.l_type = (flags & O_RDONLY) ? F_RDLCK : F_WRLCK;
  63         lock.l_start = 0;
  64         lock.l_whence = SEEK_SET;
  65         lock.l_len = 0;
  66         operation = (flags & O_NONBLOCK) ? F_SETLK : F_SETLKW;
  67
  68         trunc = (flags & O_TRUNC);
  69         flags &= ~O_TRUNC;
  70
  71         for (;;) {
  72                 if ((fd = open(path, flags, mode)) == -1)
  73                         /* non-existent or no access */
  74                         return (-1);
  75                 if (fcntl(fd, operation, &lock) == -1) {
  76                         /* unsupported or interrupted */
  77                         serrno = errno;
  78                         close(fd);
  79                         errno = serrno;
  80                         return (-1);
  81                 }
  82                 if (stat(path, &sb) == -1) {
  83                         /* disappeared from under our feet */
  84                         close(fd);
  85                         continue;
  86                 }
  87                 if (fstat(fd, &fsb) == -1) {
  88                         /* can't happen [tm] */
  89                         serrno = errno;
  90                         close(fd);
  91                         errno = serrno;
  92                         return (-1);
  93                 }
  94                 if (sb.st_dev != fsb.st_dev ||
  95                     sb.st_ino != fsb.st_ino) {
  96                         /* changed under our feet */
  97                         close(fd);
  98                         continue;
  99                 }
 100                 if (trunc && ftruncate(fd, 0) != 0) {
 101                         /* can't happen [tm] */
 102                         serrno = errno;
 103                         close(fd);
 104                         errno = serrno;
 105                         return (-1);
 106                 }
 107                 return (fd);
 108         }
 109 }