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