1/* ftruncate emulations that work on some System V's.
2   This file is in the public domain.  */
3#include <sys/cdefs.h>
4__RCSID("$NetBSD: ftruncate.c,v 1.2 2016/05/17 14:00:09 christos Exp $");
5
6#ifdef HAVE_CONFIG_H
7# include <config.h>
8#endif
9
10#include <sys/types.h>
11#include <fcntl.h>
12
13#ifdef F_CHSIZE
14
15int
16ftruncate (int fd, off_t length)
17{
18  return fcntl (fd, F_CHSIZE, length);
19}
20
21#else /* not F_CHSIZE */
22# ifdef F_FREESP
23
24/* By William Kucharski <kucharsk@netcom.com>.  */
25
26#  include <sys/stat.h>
27#  include <errno.h>
28#  if HAVE_UNISTD_H
29#   include <unistd.h>
30#  endif
31
32int
33ftruncate (int fd, off_t length)
34{
35  struct flock fl;
36  struct stat filebuf;
37
38  if (fstat (fd, &filebuf) < 0)
39    return -1;
40
41  if (filebuf.st_size < length)
42    {
43      /* Extend file length. */
44      if (lseek (fd, (length - 1), SEEK_SET) < 0)
45	return -1;
46
47      /* Write a "0" byte. */
48      if (write (fd, "", 1) != 1)
49	return -1;
50    }
51  else
52    {
53
54      /* Truncate length. */
55
56      fl.l_whence = 0;
57      fl.l_len = 0;
58      fl.l_start = length;
59      fl.l_type = F_WRLCK;	/* write lock on file space */
60
61      /* This relies on the *undocumented* F_FREESP argument to fcntl,
62	 which truncates the file so that it ends at the position
63	 indicated by fl.l_start.  Will minor miracles never cease?  */
64
65      if (fcntl (fd, F_FREESP, &fl) < 0)
66	return -1;
67    }
68
69  return 0;
70}
71
72# else /* not F_CHSIZE nor F_FREESP */
73#  if HAVE_CHSIZE
74
75int
76ftruncate (int fd, off_t length)
77{
78  return chsize (fd, length);
79}
80
81#  else /* not F_CHSIZE nor F_FREESP nor HAVE_CHSIZE */
82
83#   include <errno.h>
84
85int
86ftruncate (int fd, off_t length)
87{
88  errno = EIO;
89  return -1;
90}
91
92#  endif /* not HAVE_CHSIZE */
93# endif /* not F_FREESP */
94#endif /* not F_CHSIZE */
95