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
12
13 int
ftruncate(int fd,off_t length)14 ftruncate (int fd, off_t length)
15 {
16 return fcntl (fd, F_CHSIZE, length);
17 }
18
19 #else /* not F_CHSIZE */
20 # ifdef F_FREESP
21
22 /* By William Kucharski <kucharsk@netcom.com>. */
23
24 # include <sys/stat.h>
25 # include <errno.h>
26 # if HAVE_UNISTD_H
27 # include <unistd.h>
28 # endif
29
30 int
ftruncate(int fd,off_t length)31 ftruncate (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
72
73 int
ftruncate(int fd,off_t length)74 ftruncate (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
83 int
ftruncate(int fd,off_t length)84 ftruncate (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