/contrib/cvs/lib/ftruncate.c

 1/* ftruncate emulations that work on some System V's.
 2   This file is in the public domain. */
 3
 4#ifdef HAVE_CONFIG_H
 5#include "config.h"
 6#endif
 7
 8#include <sys/types.h>
 9#include <fcntl.h>
10
11#ifdef F_CHSIZE
12int
13ftruncate (fd, length)
14     int fd;
15     off_t length;
16{
17  return fcntl (fd, F_CHSIZE, length);
18}
19#else
20#ifdef F_FREESP
21/* The following function was written by
22   kucharsk@Solbourne.com (William Kucharski) */
23
24#include <sys/stat.h>
25#include <errno.h>
26#include <unistd.h>
27
28int
29ftruncate (fd, length)
30     int fd;
31     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      /* Truncate length. */
52      fl.l_whence = 0;
53      fl.l_len = 0;
54      fl.l_start = length;
55      fl.l_type = F_WRLCK;	/* Write lock on file space. */
56
57      /* This relies on the UNDOCUMENTED F_FREESP argument to
58	 fcntl, which truncates the file so that it ends at the
59	 position indicated by fl.l_start.
60	 Will minor miracles never cease? */
61      if (fcntl (fd, F_FREESP, &fl) < 0)
62	return -1;
63    }
64
65  return 0;
66}
67#else
68int
69ftruncate (fd, length)
70     int fd;
71     off_t length;
72{
73  return chsize (fd, length);
74}
75#endif
76#endif