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
15 int
ftruncate(int fd,off_t length)16 ftruncate (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
32 int
ftruncate(int fd,off_t length)33 ftruncate (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
75 int
ftruncate(int fd,off_t length)76 ftruncate (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
85 int
ftruncate(int fd,off_t length)86 ftruncate (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